Monday, January 31, 2005

SURPRISE SNOWSTORM FOR THE NORTHEAST?


FEBRUARY WILL ROCK...AND STORMS ARE GONNA ROLL

MONDAY EVENING UPDATE: BIG CHANGES ON HORIZON FOR THE NORTHEAST
Next post Tuesday morning about 6:30 AM

Based on your comments from Monday, which I can't read at school, many of you have picked up on the 180-reverse course-about face-egg in your face change in NWS forecasts today. The computer models are all haywire on this system, hence the consternation in forecasting. As for the big warmup? Yeah, okay...whatever. I don't mind above normal temps in early February, because it is like waving a red flag at a hungry bull in heat inside a china closet. Whatever warmup was on the table for late this week is now gone, as Baltimore NWS has..surprise! Chance of Rain and Snow, high 41 for Friday. Either way, you have to agree that restricting Arctic air in Canada for an entire week in the dead middle of winter can only mean that once it is unleashed again, the retaliation will be swift and powerful.

This has happened several times this winter already, and gives my forecast even more impetus. The storms we've had thus far were only salvos across your bow, pipsqueaks compared to what I think is on the horizon. Granted the folks in the Deep South don't think the 3/4 inch ice in Atlanta was pipsqueaky, but winter is far from done. Groundhog Phil WILL see his shadow Tuesday, and you are in for a wild ride the next 3 weeks.

Now that we are going back into "Storm Mode" I will focus attention the rest of this week on our developing winter storm situations for the Mid-Atlantic and New England.

1. BASIC FORECAST: A SERIES OF STORMS FOR FIRST 15 DAYS OF FEBRUARY.

Storm 2 : Eastern New England, Thu night-Friday. This system is really just an older version of Storm 1 that just exited the coast Sunday. It is becoming clear from a multitude of models, especially the GFS, that a re-energized version of Storm 1 will retrograde toward New England on Thursday and has the potential to deliver a roughly 3-6" in downeast Maine, and 2-4" in Eastern Massachusetts, with up to 6 inches along the Cape. nUThis will be in combination with very gusty winds and heavy wave action as you'll have a strong northerly fetch across the Gulf of Maine. This is clearly indicated on the current QPF for that time period. Why is this happening? The negative NAO, blocking in the North Atlantic due to a westward expansion of the Icelandic Low prevents storms from heading merrily out to sea. Read this simple explanantion of the North Atlantic Oscillation.

Storm 3A : Gulf/Southeast, Tue-Thu. is a system in the desert southwest and crossing Texas as of Monday night into Tuesday. There could be wet snow and freezing rain across Arkansas, Tennessee, North Georgia and NC Mountains early Tuesday morning and late Tuesday night. The Raleigh, NC Forecast Office wins the big prize for being first out of the gates with a Special Weather Statement on this system. The latest QPF (Quantitative Precipitation Forecast) shows considerable moisture as you would expect from a Gulf system. The current NAM (North American Model) shows the rain/snow line with this system by Wednesday running from eastern Tennessee to southern Virginia, so it seems plausible those areas would have an early morning snow and rain mix Thursday. This system SHOULD go out to sea near the Carolinas, right? Not so fast.

In the face of a strongly negative NAO, this beast has the potential to stall, and then spawn a secondary Low which may try to turn up the coast late this week. Meanwhile, the monkey wrench in all of this is retrograding Storm 2 heading to New England Thursday. Remember air moves counter-clockwise around a Low Pressure. The wrap-around warm air coming on the backside of Storm 2 will clash with low-level cold air over eastern New England, producing moderate snows accumulating no more than 6” in any one location. So the wrap-around moisture from Storm 2 will continue to stream southward after snowing in Mass and Rhode Island. Concurrently, a strong trough is forecast to develop over the Mid-Atlantic at upper levels. When surface moisture is injected into a developing trough, it usually spawns a new Low pressure system, which I will name Storm 3B. The only wrinkle is what effect the cooler than normal water would have on this developing Low.

Storm 3B : Mid Atlantic, Friday. This system should begin to form sometime Thursday night near the Virginia Capes. At the same time, we have moisture streaming northeastward ahead of Storm 3A. The formation of Storm 3B will absorb moisture from 3A, helping to intensify it under the trough. Now this system has TWO sources, one is warm moist air from the southeast, the other is moderated moist air from the northeast. Link all this up with an arriving High pressure from Canada, and you have the makings of a surprise late week snowstorm for the Mid-Atlantic from DC to Boston. I know it sounds very complicated. If you think I am making this up for ratings sake, check the Japanese Model (JMA) which I will put online in my links column.

The scary part is that I pretty much made up this idea today as a “what if” brainstorm, while I was trying to figure how Storm 2 and 3 would interact if they go close enough to each other. Then I learned after the fact from other discussions that I have learned from other discussions that the JMA this model has been depicting just such a scenario for sometime now.

So what we have is a BLUE BANDWAGON ALERT, I think many forecasters along the East Coast from Norfolk to Boston will find themselves hastily revising their predictions for the Thursday-Sunday period. Looks like they already started. I’ve already begun to see this reflected in the Thursday-Friday forecasts for Philly, NYC and Boston. The JMA is printing out up to .75 liquid for the Mid-Atlantic from Virginia up to southern New England. (Also need to issue a Bass-O-Meter alert to find out how much himming and hawing Marty Bass will do in Baltimore over this storm.)

The Forecast Discussions put out by Boston NWS Office are the most objective and forward-thinking of any NWS office on the East Coast. This one in particular is worth your time reading. Although I originally said Storm 3 would not turn into a Nor’easter, I now have to change my tune and make the bold call that you can kiss goodbye the 40’s on Friday, for it might actually be snowing in DC, Baltimore and Philly instead. This system is going to make forecasters very nervous this week as computer models will waffle quite a bit on this until they can resolve the energy differences between retrograding Storm 2 and the encroaching Storm 3. Will we see forecasts creep toward precip this week for the Mid-Atlantic?

Big Warmup Alert: The 48 degrees advertised by TWC for Friday in Baltimore is now 41. Wonder where the big warmup went? Hmmmm.

Storm 4 : Feb 8-10, Northeast U.S. This has been advertised on some of the computer models now for a couple days. As of Monday morning, it appears to be two separate systems. One looks to be in the February 8-10 period, and the other February 12-14 period. Either of these could become the BIG KAHUNA... like a 2005 version of the March 1993 Storm of the Century. As you would expect, there will be all kinds of model meandering over the next 2 weeks with this. I can be confident of this forecast because of the plethora of scientific data available that points to one or two very significant winter storm events brewing for February.

HOW SIGNIFICANT? Oh you had to ask... well it's your run-of-the-mill paralyzing coastal snowstorm for the Northeast... 12-24" in the major cities, airports shut down, that kind of thing, nothing you can't handle. This description is called reverse hyping. We know it will be big, so we're downplaying it's big-ness now to compensate for all the real hype later.

2. ANALYSIS BEHIND THE FORECAST
The time period from February 7 to 20 is going to be a powderhound's dreamworld, because the atmospheric signals are all beginning to align in the way we observed inJanuary 2003, which ultimately led to the legendary Blizzard of 2003. My forecasts are based on my interpretation of the models, a consideration of how NWS and Accuweather Forecasters are reading them, my study of how similar situations and storms developed, as well as my experience and intuition over the past 20 years in forecasting big winter storms.
The two graphics at top are from Accuweather, and the ones on the bottom from NOAA's Climate and Meteo Centers.

A. The North Atlantic Oscillation. Look carefully at the charts on the lower left. I apologize for them being hard to read, but just take a closer look. You will notice little black dots along the O base line. I placed these dots there to show that in the case of the January 22-23 Blizzard, the NAO immediately flipped to negative right before the storm. This is why I had a sixth sense it was coming farther north, and hence called it a Blizzard before that idea went public.

If you look to the right of the first big NAO chart, there are two smaller charts. The top smaller chart is the NAO archive for Winter 02-03. I have 5 small dots placed where major snow or cold events occured in the Mid-Atlantic and Northeast, all right around the time period when the NAO either flipped to negative, or trended back to neutral, then retreated strongly negative again. The best case for this setup was the February 2003 Blizzard. The NAO after being mostly positive the first 10 days of that month, did a quick reversal around the 15th, a day before forecasters caught on to what had been up to that point a very hard storm to peg. And everyone but Accuweather was howling that this puppy would go south, sure thing it did, huh York County?

For big nor'easters, the NAO is quite simply, the fingerprints on the smoking gun. It gives you a heads up about 2 days before a major event, or an unanticipated shift in the pattern. Any meteorologist, or member of the general public, can easily find and read the NAO chart on the NOAA websites. So if you consider where the NOAA computer ensembles are taking the index for the next 14 days, you can see why Accuweather has the cold and stormy forecast they do. Look at the general trend..heading toward strongly negative as the month progresses. As of Monday afternoon, it has resumed a much stronger negative signal. This can only mean a return to much below normal temperatures for the Northeast throughout February.

B. Water Temperature Analysis
I have visited this topic several times since October, and it is worth refreshing. The key to our weather this winter has been where the above and below normal water temperatures are located.

Below Normal: Off U.S. Southeast coast, Florida and Pacific Northwest. This lends stability to the High pressure ridge already in place, as the cooler than normal water allows sinking air above it, continually re-strengthening the High. The placement of that high helps send southern stream storms up toward the Northeast. Notice how Storm #1 trended more NE than ENE like computer models predicted? Cool water off the Pacific Northwest tends to lend stability to the ridge parked over the Rockies. This forces the northern branch of the jet stream (the northern stream) up over the western U.S., and the negative NAO signal with the blocking Icelandic Low and Greenland High FORCE the northern stream southeast across the Great Lakes and into the Northeast. The cool water adjacent to the East Coast is also a very good sign, for it was the reason our High pressure this weekend was so stubborn in leaving. The cooling, sinking air over the water tends to stabilize the pressure, keeping the High in place.

Above normal: Large patches of 4-6 C water off New England coast, 1-2 deg C water in Gulf of Mexico and extending southwest into the Pacific tropics from the west Mexico coast. That is the El Nino signal, for it keeps the southern jet stream continually fed with moisture as it traverses across Mexico, and into the Gulf.

The correlation? The confluence of all these events has to come together in the right orientation to get a big East Coast snowstorm. At present, it sure looks like everything is starting to dance according to the music. Later this week, the blocking signal from the NAO will send the northern stream southeast, just in time for the southern stream to get squeezed north by the Atlantic ridge. Where the two streams meet will be above normal water in the Northwest Atlantic, and cooler water just to it’s southwestern flank. That cooler water allows cold Arctic highs to set up show right along the coast. When the two streams meet, or PHASE over that water and in this atmospheric orientation I have described, you have the Perfect Storm(s). We had a very similar setup in February 2003… a warm start to the month, followed by a surprise snowstorm on the 6th, then a second but shorter quiet period leading up to the BIG KAHUNA which began on the 14th and continued until the 17th.

So when is this BIG KAHUNA? I think the time frame looks to be February 8-10, when all the elements will be in place for something very very big to happen along the East Coast. When this occurs, I’m sure that the A.P.P.L.E. will be brightly beaming with pride. (That’s an special, exclusive branch of the powderhound association, kind of like the Red Hat Society. Membership is given only to those with three full cans of snowblower gas, 32:1 mix.

3. THE PHILOSOPHY BEHIND THE ANALYSIS
Sometime Tuesday or Wednesday, for now we will focus on the evolution of Storm 2 and 3A/3B.

Sunday, January 30, 2005


GIVE A LITTLE BIT...
give a little bit of your love to me. - Supertramp

That's what all us powderhounds here in the Mid-Atlantic are singing today, as we continue to hope that it just keeps piling up. Storm 1A faded as planned in West Virginia, and Storm 1B is off the North Carolina coast. It appears to be moving out to sea, but the radar indicates snow seems to end, and then redevelop on the back side near Frederick County, MD. We just want it to give a little bit, so there's enough to go out with the baby and make our first snowman!
This picture is from this morning on my street in Dundalk, MD...2.5 inches here out of 3 predicted, which is an 83% and a B for the hometown storm grade.

Sunday morning, the 2-day NAO observations showed a trend back toward more negative. That could signal trouble in the Northwest Atlantic later this week, as most of the computer models now show Storm 1B retrograding back toward New England later this week. Will it be a surprise snowstorm? Doubtful, because after the Jan 22-23 Blizzard, I think all eyes are more tuned to any potential for a blue bandwagon storm. The Taunton, MA NWS office is keeping a close eye on this, read their Forecast Discussion for details. Until I update later tonight, check out the model links on the right (no, they're not magazine models) to get a sense of what computer are indicating for the next set of events later this week.

I have to do some grading, in the hopes that if I do my schoolwork now, we'll have a delay tomorrow. Trying to second guess Murphy's Law there. If I don't do my work, then school will open EARLIER instead of on time. Later today, a final wrapup on the storm when it is over, what we learned and what is in store for the next 2 weeks.

Hoping for some re-freezing tonight, but NOT for those of you who have to drive in it anyway.


Saturday, January 29, 2005

INSIDE US ALL IS A KID WHO LOVES SNOW



SATURDAY EVENING MINI-UPDATE:
Thanks to all for your comments, questions and observations. Our daughter is celebrating the snow with you, as that is a picture I have been waiting a long time to take...her with snow falling out of the sky. She has just begun to say small words, and would you be surprised that "SNOW" is one of the words she loves to say. I hope she'll have many more oppportunities to say it in the near future.

A couple observations before bedtime:

1. I think it is obvious from radar, the obs map, and Accuweather's graphics that this puppy is coming farther north. The heavy snow that many forecasters, including me, expected for south western Virginia may not materialize, and in reality, the area of heaviest accumulation may be shifting east and northeast.

2. I am concerned about the upper level Low (which I consider Storm 1A) in Kentucky. Paul Kocin on the Weather Channel says this system may come directly east, and redevelop off the coast. I have seen previous upper level systems activate snowfall in the Baltimore metro area, from tapping Bay moisture...basically "Bay Effect Snow" if there is such a thing. Sunday, Jan 5, 2003 is a prime example. An upper level feature came right across central/southern Maryland, and what was predicted to be flurries turned into 4 inches of snow. This system reached the coast, redeveloped somewhat, and wrap-around started, giving us another 1 inch. The punchline is that this extra inch began to fall at 5:00 AM, just as schools were deciding to open or not.

Baltimore County decided to close. Then at 7:00 AM, the snow stopped, sun came out and the day was fine! Do I think this will happen again? The dynamics are the same, there is certaintly plenty of moisture around. The main issue is if Storm 1B currently the Gulf will redevelop along the Carolina Coast or not.

3. North Carolina: In NC, what was thought to be heavy snow is turning out to be heavy ice. Temps have been a conundrum all day for forecasters. It is a simple fact this High meant business and we saw that going into this storm. I think the cold air damming down east side of the Appalachians was underestimated, as has been the moisture feed from the Atlantic. If you get any snow, it will lend to a lowering of temperatures, because this is called "evaporative cooling." As the moisture crystallizes into snow, this process takes heat OUT of the atmosphere, and as the snow falls, I like to say it "brings the temperature down with it." That would mean you are in for general right around 32 F tonight. If the coastal develops, I think it will capture cold air from up my way, and the wrap-around effect will send that cold air your way, potentially refreezing that slushy ice tomorrow night.

4. Next Week's Storm. A lot of variance in the models. The JMA (Japan Meteorological Agency Model) is predicting a hybrid nor'easter type thing, and the GFS is hinting at something as well. I will do a roundup on what models are saying and what I think they are telling us. If you want the total inside scoop on this for the moment, the Boston NWS Forecast Discussion has outlined the possibilities, which I will analyze in detail on Sunday. For now, it is becoming more clear that something bizarre is in the offing for the middle and latter part of next week for Southern New England.
HERE IT COMES...READY OR NOT

SATURDAY PICTURE SHOW ROUNDUP:
Freezing rain and sleet have held on tough overnight and into the morning throughout the Deep South as you can see from the radar. One quarter to three quarters inch ice accretion is expected. The big culprit is of course our large High which has refused to give up any ground, and is stronger and colder than expected, now parked over the northern Del-Mar-Va. This was clearly pointed out in my previous two posts as the reason why the storm might end up being stronger, more snowy, and come a few miles farther north than anticipated. Keep an eye on the 'Current Observations' map for a real-time look at where the storm is.


If you are new to the site, scroll to the post below for the forecast on this storm.
The NWS has advanced the onset of precipitation by a few hours or so in the DC-Baltimore regions, then backed off to late tonight again. The Philadelphia NWS has hoisted the Winter Storm Watch flag for parts of the Del-Mar-Va. Baltimore NWS keeps flipping back and forth between all snow and a mix, and alluded that amounts are a shade below "warning criteria." I believe these factors are an indication the storm is starting to show signs of creeping farther north than we anticipated.

I know to New Englanders and others used to a lot of snow that this seems a lot of fuss over less then 6 inches of snow for most areas. My issue is that this is a Gulf-Altantic coastal Low, so it has lots of time to tap lots of moisture. With that high drifting off the coast, is it possible the return flow shoves our storm a teensy bit more north and west? I think so. You can see from the Obs and Radar Map that this thing is going to town as the moisture makes it's way northeast. I make this storm a big deal because of my belief it has the potential to come farther north and cause a lot of problems for the Mid-Atlantic from DC north. I believe we also have the makings of the secondary Low forming off the South Carolina coast.


Lunchtime update: NAO has begun to trend back to more slightly negative as of today. I could just be overly enthusiastic because I love storms, but it is also a sign that this current storm may have a few surprises left in store for those of us south of the Mason-Dixon Line. The only changes I have made to the snowfall grades is to Richmond... it was 2 inches and I will raise that to 4 inches.

Big Warmup Update: TWC forecast for Baltimore on Friday was 47 two days ago. Now knocked down to 43. Humpf, wonder why that it.

Snowday Potential: I think a delay is likely for Baltimore-DC metro area schools Monday, especially if there is re-freezing. From Richmond northwest to Harrisonburg, south to Roanoke... NO SCHOOL Monday.

Crystal Ball Alert for next big storm: I will do a re-analysis of the big storm potential for next week. Folks, it is still on the table given the NAO and an active southern stream. I have convincing evidence and actual observations from atmospheric dynamics that Storm 2 is lurking in the near future (7-9 days) for the East Coast, despite whatever your local TV or internet news outlet may say. But I have family visiting today, and it is playtime with my daughter, who has been away for a week. I will post that analysis late this weekend...before school Monday.

Friday, January 28, 2005

VIRGINIA IS FOR LOVERS...SNOWLOVERS THAT IS

FRIDAY EVENING ROUNDUP:

- Updates to the snowfall forecast, since we are about 24-36 hours away from onset in the Mid-Atlantic, I have posted “graded amounts.” This is the single number on which the storm forecast will be graded for that area.

- There are some changes to the schedule for Storm 2, but I am not back-pedaling or trying to tweak and make you forget I forecasted a big storm, because it is still on the table. Computer models are having difficulty finding and then projecting this storm in the near term, and I can't simply create a storm out of nothing with no modeling basis. However, the pattern which will produce Storm 2 in the next 7 days is still firmly in place, it’s development is simply pushed back a couple days, whether it comes from the west, south or east. This is covered in the “Philosophy” section at the end.

- Beyond the Philosopy section is the schedule of my observation-analysis-forecast-post cycle, so you know when I update and don't have wait unnecessarily for it if it's not coming for another few hours.

1. WEEKEND STORM FORECAST

1-28 Update: The next 2 days will feature a highly complex storm moving out of the Southeast and into the Mid-Atlantic States. The areas affected with winter precipitation by this first system include the Tennessee Valley, Carolinas, Virginia, West Virginia, Maryland and Delaware from Saturday into Monday morning.

STORM 1A is now a series of Low pressure systems spread between New Mexico-Louisiana and Florida. A primary Low will emerge out of this, and will move to a position near Chattanooga, Tennessee by Saturday afternoon. Meanwhile, a large, very cold high pressure system has been dominating the East Coast from New England to Georgia. Cold air has filtered much farther south than originally anticipated, prompting winter advisories, watches and warnings into central Georgia and west central Alabama. Significant icing of up to 1/2 inch as well as wet snow is possible throughout the Southeast from central Alabama northward to Tennessee, northeast along the Blue Ridge Mountains to the Shenandoah Valley, including western and interior areas of North and South Carolina. On Saturday and Saturday night, rain is expected along the coast in areas from Richmond south to Raleigh-Durham.

STORM 1B is a secondary Low pressure that may develop along the North Carolina coast on Sunday, move northeast and draw in moisture from the Atlantic. This storm has the potential to change rain along the Virginia coast over to snow as it departs on Sunday night. At issue is the arrival of a fresh high pressure system to the north, which would recharge the area with cold air, enabling storm development.

STORM 2 is presenting an interesting situation, as several computer models have begun to show Storm 1 moving out to sea, then BACKING NORTHWEST toward New England. I am not making this up. As indicated before, this is a highly complex system which must be watched closely for unexpected changes in the outcome. It is also possible this is a "feedback error" in the modeling which tends to rectify itself within a few days, leading to the possibility that Storm 1 has the potential to stay closer to the coast. More information will be known within 24 hours once we see how Storm 1 begins to pan out in North Carolina on Saturday.

2. REGIONAL FORECAST (Saturday to Monday morning)

North Georgia to Carolinas: Snow, sleet and freezing rain in mountains on Saturday late afternoon into the evening, and light rain changing to snow and sleet in northern Atlanta. Interior western SC and NC will see freezing rain and sleet, causing possible power outages depending on amount of ice. Snow amounts of 2 or more inches are likely, with ice accumulating from 1/16 to 1/8 inch. Interior and western Carolinas will see ice amounts of up to 1/4" This will become a major, near-crippling ice storm for this region.

Virginia-West Virginia: Low 1A will produce interior mountain snows accumulating 6 or more inches starting Sunday early morning. Snow also begins early Sunday morning in the piedmont and coastal plain, changing to sleet, freezing rain, and rain along the immediate coast as the daytime warming occurs. Areas impacted include Charlottesville northwest to Harrisonburg, and then southwest beyond Lynchburg and Roanoke. Richmond will see snow change to sleet and then rain.

Maryland and Del-Mar-Val: Metropolitan DC and Baltimore northeastward to the PA line will see snow begin around midnight Saturday, moving from south to north, and accumulate 2-4 inches by evening Sunday. A mix with and changeover to sleet and freezing rain overnight Sunday is possible. A changeover to all rain along Del-Mar-Va coastline is likely until Low 1B begins to pull down colder air from Canada.

Pennsylvania: Previous storms which were expected to stay south of the PA-MD line have moved farther north than expected. If Storm 1A stays south, and Storm 1B forms and moves away as predicted, then snow amounts north of the PA border will be 1-3 inches.

Metro Philadelphia will be impacted by the leftovers of Low 1B of Sunday night-Monday, where a brief period of wet snow may develop in southeast NJ and along the Delaware coast as the storm pulls away.

New York City-Long Island-New England: Little or no impact to areas farther north of Philadelphia from Storm 1A or 1B.

STORM 1 : SNOWFALL and ICE PROJECTIONS

The overall trend is 2-4 inches from Baltimore City north to the PA/MD state line. 3-6 inches from Baltimore City south and west toward DC and northern Virginia. 5-10 inches in central and southwestern Virginia/western North Carolina/western South Carolina.

The numbers on which the storm will be graded. This assumes there is a 2” variance on either side of the grade number is you do not live at the exact location mentioned.

Overall is 2-4 inches from Baltimore City north to the PA/MD line. 3-6 inches from Baltimore City south and west toward DC and northern Virginia. 5-10 inches in central and southwestern Virginia/western North Carolina/western South Carolina.

Central PA (south of I-80, north of I-76): Less than 1 inch. Grade location: State College, PA.
Southern PA (south of I-76): 2" Grade location: York, PA

Metro Philadelphia: 2" Grade location: Phila Int’l Airport

North Central Maryland (North Balto County above Beltway, Harford, Cecil):
3" Grade: Towson, MD

Central-Southern Maryland (S Balto County/City to DC Beltway): 3.5"
Grade location: Laurel, MD

DC Metro: 4" Grade Location: Dulles Airport

In Virginia: Richmond, VA: 2" Lynchburg, VA: 7" Roanoke, VA: 9"

3. SCIENTIFIC ANALYSIS

WHAT AWAITS US AS WE HEAD INTO FEBRUARY?

This is a late-breaking development just in the last few hours, but it merits discussion. Something weird is starting to develop around Day 3 with with Storm 1 in the Atlantic. Go take a look at the UKMET and ECMWF if you want a glimpse. Do you notice how these models take Storm 1 off the NC coast, then they don't know what to do with it. The northern high appears to be blocking it from making northward movement. Could it be that the models are misreading upper level patterns and the real outcome is a more northeasterly track for Storm 1 along the coast TOWARD New England. The Boston NWS picked up on this new wrinkel early in the evening on Friday. Here are their comments.

There is still quite a bit of uncertainty beyond Monday in this forecast. Strongly negative North Atlantic Oscillation not expected to break down during this portion of the forecast. Thus expecting the various shortwaves during the middle of next week to only deepen the mid level trough across the northeast.

Though for the most part, high pressure over the midwest is expected to keep the track of any low pressures well to our south or east. however, there are a few gfs ensemble members, as well as the 12z run of the ukmet, which actually retrograde a storm over the North Atlantic toward Southern New England. Given the uncertainty, this should be considered a long shot at this time, but still something to keep an eye on.

I reason I believe this type of random changes is an example of pattern we are in that favors rapid development of large, widespread snowstorms we have come to associate with February. Here is my case for continued storminess, based on a detailed analysis of current data.

- The NAO remains negative, and while it has retreated towards neutral somewhat, is forecasted to go mild to strongly negative once again by February 1, and then trend further down from there. This would indicate more storminess and cold weather on the East Coast, due to the westward movement of the Icelandic Low, and the Greenland High backing toward Eastern Canada. This tends to block storms from heading out into the Atlantic, and allows them to impact the coastline. Also, heavy snowpack from PA northward is going to hold down temperatures next week to normal, which will allow some melting, but not a total loss of snowpack as the GFS usually advertises. I saw a forecasted high of 47 F for next Friday in Baltimore. Okay, sure. What was the forecast for this Friday on Monday? Wasn't it in the 50's almost? Today's high in Baltimore...27 F.

- A persistent “cross equatorial trough” exists in the upper levels of the atmosphere from off the Mexican Pacific Coast extending down into the western Pacific off tropical South America. This argues for tremendous moisture potential to be tapped at any time by the subtropical jet currently streaming into the Gulf of Mexico.

- Above normal temperatures in most of central and southern Canada force the northern (polar jet stream) to take a more southerly track, around the southern fringe of the warm air mass. This meshes well with a Polar Pacific High parked over the Rockies. So the northern jet can swing over the top of the high, travel southeast under the Canadian provinces and toward the Mid-Atlantic. This is called "split flow" and it results in the two streams eventually coming closer together down east.

- Much above normal water temperatures off the East Coast. This argues for enhanced moisture feed into developing coastal storms. This water may play a big role in the outcome of Storm 1 on Sunday for the Mid-Atlantic, as well as the newly alluded to possibility of this same storm retrograding toward New England perhaps Tuesday. Were that to occur, this already deepened Low pressure would have tremendous moisture available with which to work. And by then a fresh high would have arrived in upstate New York.

- Cooler than warmer temperatures off the Georgia/Florida coast argues for the persistent High that’s been there to remain. The clockwise flow around this high creates a southwest to northeast air flow along the coast. This airflow would prevent any storms coming eastward across the Deep South from just going out to sea, but push them a little farther north.

All these issues argue for any warmup in the East to be very brief, limited to perhaps one day like this week was on Wednesday. The blocking Greenland High and Icelandic Low, along with other upper level factors in East Asia, will keep sending shortwaves (small Low pressure systems) along the northern jet stream, reaching the coast every couple days. Each of these systems has the potential to develop rapidly, just like the "Clipper Blizzard."

4. PHILOSOPY BEHIND THE FORECAST

This is the part where we get to consider what is possible, given the pattern we are in. And it follows my philosophy that computer models underestimate how far north a southern origin storm can move, as well as how I might fail in my attempt to make the big call.

HOW THIS FORECAST BUST

- The NAO, while still negative, has begun a slight trend toward positive. This would argue that the storm ends up being warmer than I think, and more in line with that the NWS has on the table.

- Placement of Arctic high in upstate NY is not stationary. Projected to move east to southeast, and this is not the best arrangement for a classic East Coast snowstorm.

- Low level cold air should decay by Sunday in Mid-Atlantic, given that the high has been in place now since Thursday morning.

HOW THIS FORECAST TURNS INTO A SURPRISE SNOWSTORM

- A change of 25-50 miles north means the zone of heaviest snow shifts from south of DC to the Baltimore metro region, turning a general 2-4” into 4-8” and a Winter Storm Warning.

- A change of 50-75 miles means the entire Mid-Atlantic I-95 corridor from DC to Philadelphia receives 4-8 inches, with higher amounts in the immediate western counties as wrap-around in the colder air will increase the snow ratios.

- or...perhaps the computer models are not correctly interpreting Storm 1's movement as it relates to the High. Instead of sending the Low out to sea, the High noses out into the Atlantic more than we think it will, and the return flow actually drives the Low more north into the cold air.

5. POST SCHEDULE

This is not self-aggrandizement, I just figured that it would help if you really wanted to know when I post and when I don't. It is a simple schedule, so

- Weekday mornings: I get up around 5:00 AM, do a roundup of all the models, forecast discussions for areas in question, radar, upper air data, and NWS forecasts. I also read your comments right away, to make sure I account for your questions in the post. I do not pay any attention to TWC or Accuweather 15-day forecasts, because they are tied to the GFS. Then by 6:00 or so I am ready to start the post, which I usually complete by 6:30. In between this I munch on my cereal or oatmeal.

- Weekday afternoons: I check model changes during the day at lunch, and see if there are any changes in NWS discussions. Again, forget AccuWx or TWC. I can't read comments at school or post to the site, as blogger.com is blocked by our school server. That's okay, probably better that I focus on my real job during the day.

- Weekday evenings: When school is over and the dust/papers/mail/meetings/email settle, I do another round of checkups, and look at NOAA data also. I do a draft of the evening post, and at home my wife and I read the comments to each other, it is fun reading what you have to say! After our daughter goes to bed, I finish the post and put it online by 9pm if I can (except in storm mode, or on nights like this when there is more time). I do one more check of my favorite data sites before bed. Then the cycle starts over. I enjoy it quite a bit, helps put some thrill into the dreariness of winter, provided that you don't get hurt in the storms I forecast.

Next update Saturday morning, along with answers to your questions.

Thursday, January 27, 2005


LET'S GET READY TO RUUMMMMBBBLLLEE!

Thank you for all your comments and questions today, and welcome to new readers in West Virginia and North Carolina. I first want to put out my statements on the storms this coming weekend and early next week. Then I will go back later this evening and revisit your questions and do a "picture show" post where I will provide straight-forward answers based on the science behind the storm. Between now and then is dinner with my wife, and then we will do storm preparations. Hint.

1. BASIC FORECAST FOR NEXT SERIES OF STORMS

1-27 Update: The next 4 to 6 days will feature a highly complex and widespread series of storms for the Eastern two-thirds of the United States. Four separate but inter-connected storm systems will affect the Great Plains, Ohio Valley, Southeast, Northeast and New England from Friday well into Wednesday.


A large, very cold high pressure system will dominate most of the East Coast from New England to Georgia well into Sunday. A large, slow-moving, moisture-laden Low pressure system has developed on the fringe of this high in the southern Rockies (Storm 1) There is a second system now developing in Arizona (Storm 2). Each of the two Storms (1 and 2) will spawn a secondary Low along the East Coast in different locations, thus the end result will be four distinct storm systems.

If you were hoping for a simple solution, then all I can say is that it will probably snow, sleet and ice where you live if that's anywhere north or east of Atlanta between Friday night and Wednesday morning. But this is an extremely complex storm that has thrown the computer models into a conundrum. I have tried to break it down as succinctly as I can.

STORM 1 will move across the Southern Plains and into Tennessee Valley toward the Mid-Atlantic by Saturday. By early Sunday morning, the primary Low pressure (Low 1A) will reach West Virginia. By Sunday morning, the first high is sinking south and east, and a new Arctic high moving southeast from Canada will send a reinforcing surge of cold air into the Northeast.

Low 1A will affect Northern Georgia, interior South and North Carolina, eastern Tennessee and Virginia with significant icing of up to 1/2 inch as well as heavy wet snow. Concurrently, a secondary Low pressure (Low 1B) will develop along the Carolina coast, move northeast and draw in considerable moisture from the Atlantic. The second Arctic high will provide a fresh supply of cold air to allow Low 1B to become a significant coastal storm, producing snow, sleet, freezing rain and some rain affecting the I-95 corridor from Washington north to the metropolitan areas of Philadelphia. Other regions to be significantly impacted by this storm include interior North and South Carolina, the Shenandoah Valley of Virginia, southcentral Pennsylvania, coastal New Jersey and parts of Long Island.

STORM 2 will follow the heels of Storm 1, with a Primary Low pressure (Low 2A) taking more southerly track, and reaching the Tennessee/NC border by Monday afternoon. A secondary Low pressure (Low 2B) will also develop near the North Carolina/Virginia coast, deepen rapidly, and head north-northeast by Tuesday morning. This system will move slower due to a blocking Arctic high pressure system which will fill in behind the wake of Storm 1.

Both events will bring a long duration of winter precipitation over a period of several days, and may become very significant storms for the I-95 corridor from Atlanta to Boston.




2. REGIONAL FORECAST: STORM ONE (Saturday to Monday morning)

North Georgia to Carolinas: Snow, sleet and freezing rain in mountains on Saturday late afternoon into the evening, and light rain changing to snow and sleet in northern Atlanta. Interior western SC and NC will see freezing rain and sleet, causing possible power outages depending on amount of ice. Snow amounts of 2 or more inches are likely, with ice accumulating from 1/16 to 1/8 inch. Interior and western Carolinas will see ice amounts of up to 1/4" This will become a major, near-crippling ice storm for this region.

Virginia-West Virginia: Low 1A will produce interior mountain snows accumulating 6 or more inches begins Sunday early morning. Snow also begins early Sunday morning in the piedmont and coastal plain, changing to sleet, freezing rain, and rain along the immediate coast as the daytime warming occurs. Areas impacted include Charlottesville northwest to Harrisonburg, and then southwest beyond Lynchburg and Roanoke. Richmond will see snow change to sleet and then rain.

Maryland and Del-Mar-Val: Low 1A will produce interior mountain snows in western Maryland, accumulating 6 or more inches. Metropolitan DC and Baltimore northeastward to the PA line will see snow begin around midnight Saturday, moving from south to north, and accumulate 2-4 inches by evening Sunday. A mix with and changeover to with sleet and freezing rain overnight Sunday is possible. A changeover to all rain along Del-Mar-Va coastline is likely until Low 1B begins to pull down colder air from Canada.

Pennsylvania: Low 1A will produce some interior snows near and just north of the Pennsylvania border, but any heavy accumulations should stay south of I-76. Overall, accumulations of snow and ice will be higher farther south and lesser to the north. A changeover to sleet, freezing rain, and rain is possible on the WEST side of the Appalachians, due to cold air in place on east side of mountains. Snow totals from Low 1A in southcentral PA are 2-4 inches by Sunday late morning, before a brief changeover to sleet and freezing rain.

Metro Philadelphia will be impacted by Low 1B of Sunday night-Monday, where heavy wet snow will develop from southeast to northwest, overspreading the area by midnight Sunday. Accumulations will be generally 3 to 6 inches of wet snow, with some locally higher amounts in the far western suburbs.

New Jersey-New York City-Long Island: Some impact from Low 1B, as the developing coastal system pulls away. Main impact will be felt from Storm 2A and 2B. Coastal Low 1B begins to rapidly develop Monday morning along Virginia/Carolina coast. Some fringe snows will reach NJ and NYC, but accumulations will be less then 2”. By late Monday afternoon, wet snow will spread across coastal regions of Long Island and New Jersey, ending by midnight Monday. I still think this region has the potential to get hammered by Low 1B.

Southern and Southeastern New England: The track of the secondary Low 1B is expected to go northeasterly, thus precipitation is likely to avoid most of New England except for extreme southern areas such as Martha’s Vineyard. The main impact to this area will be the Storm 2’s primary and secondary lows, which will not reach this region until Tuesday. A Canadian high filling in the wake of Low 1B will deliver fresh Arctic air to the region, allowing almost all the precipitation from Storm 2A and 2B to be snow.

STORMS 1A & 1B: SUMMARY OF SNOW and ICE PROJECTIONS

Interior and mountainous regions of Southeast/Mid-Atlantic: 4-6 inches

Metropolitan and Interior areas of Central and North, Georgia, N and S Carolina:
2 or more inches of snow, followed by 1/8 to 1/4 inch ice

Metropolitan areas of MD/Northern VA/SE Pennsylvania: 2-4 inches

New Jersey/New York City: 1-2 inches

Southern/Southeastern New England: light accumulations (Storm 1 only)

STORM 2: EARLY PROJECTIONS FOR SNOW and ICE

While the precise dynamics of this second system are still being analyzed, it is becoming more apparent that cold high pressure will be in place as Primary Low 2A and Secondary Low 2B arrive on the East Coast Monday. It is possible that extremely significant snows will result over a very large portion of the Coast from the Carolinas northward to New England. A persistent snowpack over most areas from the Mason-Dixon Line on north will insure lower-than-expected daytime and overnight temperatures, thus snow ratios in Storm 2 will be much higher. I cannot give estimates as this time, but suffice to say that the “Storm C” description outlined in a post earlier this week would be the basic idea for Storm 2. That one is likely to be the major east coast blizzard type event I have been alluding to all week, and Storm 1 is just the front-runner.

2. ANALYSIS OF FORECAST

I have reviewed the latest NWS forecast discussions along the East Coast this evening. You can too, just click on the name of the city under "Forecast Discussions" and scroll down to where they start talking about "Long Term." Here is an example from the DC-Baltimore office which is alluding to my version of the storm evolution. First paragraph is this morning, second paragraph is this evening.

MORNING 1-27: GFS AND ECMWF BOTH TRACK THE SFC LOW TO THE SOUTH OF THE REGION FROM THE LOWER TN VALLEY...ACROSS THE VA/NC BORDER AND THEN NORTHEAST ALONG THE EAST COAST. THIS TRACK COULD PRODUCE SNOW...BUT WELL TOO EARLY AND WILL STAY WITH CURRENT FORECAST OF RAIN/SNOW MIX.
EVENING 1-27: GFS SUFFERING FROM LESS THAN DESIRABLE CONSISTENCY. GIVEN MDL DIFFICULTIES IN INTERPRETING A CMPLX PTTN...HV STAYED CLOSER TO AN ENSEMBLE/PERSISTENCE FCST... STICKING TO A CPL OF PRINCIPLES. THESE ARE... 1/ PTYPE SHUD START AS MAINLY SNW...SINCE THERE WL BE A DRY AMS TO EVAP MSTR INTO... 2/ WAA WL YIELD AT LEAST SOME MIXED PCPN...AND THE MIX WL BE GREATER IN SRN/SERN SXNS. UNSURE ABT QPF AMT...NOT TO MNTN PTYPE. A GENERIC SPS WIBIS TO HIGHLIGHT A POTENTIAL WEATHER EVENT. ALSO...HV UNDERCUT MAXT TO BE MORE IN LINE W/ MIXED OR FRZN PCPN.


I can tell you that I believe the fingerprints on the smoking gun is the current trend of the NAO. Read Tuesday's post about the North Atlantic Oscillation. It is a statistical improbability that a storm will go up west of the mountains during a negative NAO, or turn to all rain along the East Coast. Just ain't gonna. As a result, you will see NWS forecasts start to trend colder and more snowier with time, as they pick up on this trend, which as of this evening, it appears they are starting.

Here's snippet from the Boston NWS Office: (I expanded their abbreviations)

"Storms, model ensembles and operational runs from the gfs/ecwmf and ggem all support several coastal events somewhere from the Carolinas to New England next week and beyond. Long term, later..low pres/snow risk Sunday should be for the snow starved region of the Mid Atlantic south of the Mason Dixon line while a secondary cold front gets stuck here in SE New England awaiting further and more important mid Atlc coast developments for Tue/Wed as now agreed by ecmwf/gfs operational runs."


And the Raleigh-Durham, North Carolina NWS Office is beginning to see the colder trends I have been talking about... (caution, this is long. The caps are their doing, not mine. Trust me, they are not shouting at you.)

WHAT LOOKED LIKE MORE OF A QUICK NUISANCE ICING EVENT YESTERDAY NOW LOOKS A LITTLE MORE DIRE. THE 00Z/27 GFS CAME IN DRASTICALLY DIFFERENT FROM ITS PREVIOUS RUN... AND CLOSER TO THE FORBODING ECMWF... WITH ITS DEPICTION OF A COASTAL CYCLONE DEVELOPING OFF THE SE COAST SAT NIGHT... EXITING SUN NIGHT... AND FOLLOWED BY ANOTHER LOW APPROACHING FROM THE WSW LATE MON. THE MID LEVEL WAVE THAT THE GFS BRINGS ACROSS THE OH VALLEY/MIDATLANTIC LATE SAT THROUGH SUN IS A NEW FEATURE WITH THIS RUN & LOOKS TOO STRONG SO HAVE IGNORED ITS ASSOCIATED QPF BULLSEYE...

And here's Philadelphia recognizing how the GFS has led us astray with it's "BIG WARMUP"

1-27 MORNING: THE GFS HAS TRENDED COLDER DURING THE BEGINNING OF NEXT WEEK...WHICH BRINGS IT MORE INTO LINE WITH THE OTHER MODEL GUIDANCE. THE GFS HAS BEEN THE OUTLIER...WITH ITS WARMTH... FOR THE PAST FEW DAYS. HOWEVER...IT CONTINUES TO BE THE MOST ROBUST WITH THE MOISTURE AND ENERGY APPROACHING THE REGION TUESDAY AND WEDNESDAY.

1-27 EVENING: THE HIGH OVER THE AREA GRADUALLY PUSHES AWAY AS LOW PRESSURE TRIES TO MOVE UP FROM THE SOUTH. HOWEVER, IT APPEARS ON THIS LATEST 12Z RUN THAT THE HIGH MAY BE STRONG ENOUGH TO KEEP EVEN ANY SMALL EFFECTS IN THE SOUTHERN HALF OF THE AREA SUNDAY INTO SUNDAY NIGHT. ANOTHER SURFACE WAVE APPEARS TO WORK SOUTH AND EAST OF US EARLY NEXT WEEK, BUT THE ASSOCIATED UPPER TROUGH COULD PLAY A ROLE IN GENERATING MIXED PRECIPITATION (DEPENDING ON LOW LEVEL TEMPERATURES) INTO TUESDAY NIGHT. CONFIDENCE AT THIS POINT IS LOW, BUT IT DOES NOT APPEAR TO BE A STRONG STORM FOR US WITH A LACK OF PHASING BETWEEN LOWER AND UPPER LEVELS OF THE ATMOSPHERE.


We'll see about that last part.. no phasing of the streams? We shall indeed see what happens.

3. PHILOSOPHY BEHIND THE FORECAST

I developed the storm descriptions you read above yesterday, then revised them today around 1:00 PM during my lunch break, before the newest run of models came out, and before the NWS started hoisting the storm flag. Then I noticed afterwards that Accuweather started trending colder in their forecasts, as has the NWS in Baltimore, Philly and Boston.

I am not going to flop around each time the models change. That's why you see a different, bewildering forecast on the Weather Channel every 6 or so hours. I think some offices at the NWS are once again blindly following the GFS, while others are recognizing it's demonstrated weaknesses thus far this winter, and are not giving it a lot of credence right now. There is huge disparity in the modeling for this storm, but the one constant that IS GOING TO RECTIFY ALL FORECASTS toward a snowier stormier solution is the negative NAO. It cannot be denied.

This is an extremely complex situation that we have not seen in a long time. These 2 storms will probably be harder to predict than the February 2003 Blizzard, and the complexities will lead to even more variance in the forecasting as we get closer. Be prepared to see almost every time of solution imaginable even up to 12 hours before the event, some will say all rain, others will say all snow, and most everyone else in between.

If I end up being way out in left field, and it rains all over the place for three solid days starting Sunday, and Boston washes down into the harbour, then I will gladly explain why my forecast went wrong and what lessons can be learned from it. I do notice how TV forecasters are hedging quite a bit and trying to resolve how the colder air redelivery will impact the secondary Low. I just don't think you can have a large moist Low heading through the Ohio Valley, given this pattern, and NOT have a secondary develop off the coast, pull in colder air, and bomb out on it's way to New England. I think you ignore that possibility at your own peril.

I believe the TWO primary storms have the potential to surprise a lot of people with higher than expected amounts of snow, ice and wind...given that they each will spawn a secondary. And... this has been said before...THE STORMS ARE GOING TO COME FARTHER NORTH THAN EXPECTED. There is a rain element in both storms, but not a total washout, and confined to a few hours of daylight in the north, or in right along the coastline south of Philadelphia.

These events are the beginning of an extended period of record-setting period of storminess, snow and cold for the Mid-Atlantic, Northeast and New England. I said earlier this week that there would be at least 3 major storms for the Northeast over a short period of time, each storm getting progressively worse, more intense, and snowier. Now it looks like that number should be 4. Accuweather has alluded to this in a graphic this morning. The next major event looks to occur next weekend, and it could be...well, extremely significant. Yeah, I know you hate that word. It is so overused these days. So I'll just say it. Translate significant into SNOWSTORM. Florida got 3 hurricanes in a 30-40 day period, why not 3 blizzards/major storms.

Tonight or tomorrow, I'm going to get a LARGE RED gas can to be my main supply, from which I can create the oil-gas mix for my snowblower, just in case I am unable to go anywhere for a couple days. Or in case I have to plow out 6 inches of heavy wet snow. Bostonians... recommend you clear off your roofs soon, so you are ready for anything.

CONSIDER SOME WHAT IF’S…WHY I THINK FORECASTERS ARE HEDGING

WHAT IF…The high currently in place stays longer or ends up being stronger than forecast. Weekend temps will end up being lower than we expect, and thus temps at onset of the storm are several degrees below what is currently forecasted.

WHAT IF the high moves a bit southeast instead of due south as GFS is predicting. This will capture more of the Northeast under the cold dome well into Sunday.

WHAT IF the second High coming in Monday simply links up with the first high. This would give rise to a situation where we thought we’d have “retreating cold air” as Accuweather has stated, and instead we have “firmly entrenched” cold air into which all this Pacific, Gulf and Atlantic moisture is driven.

WHAT IF
the Storm 1 moves in quicker than anticipated, and the high moves out slower. Then you have precipitation arriving during the overnight hours either Saturday night or early Sunday morning. Overnight precip is going to be mostly snow, and evaporative cooling will lower the atmospheric temperature a few degrees, eliminating any changeover to rain on Sunday. The Baltimore NWS finally recognized this potential and went with a Special Weather Statement today. It’s all about the Negative NAO. Accu-weather forecasters follow this mantra… “If you predict the High, then you’ll predict the storm.”

And that’s what I’ve been focusing on… where will the High be and how strong once it is there. If you've read all the way to this point, CONGRATULATIONS. You are a true blue (white) Powderhound. Again, I will review your questions this evening and post a response later tonight with some pictures to back up the answers.

Regardless of what happens, it will be an exciting weekend.


BEHIND SOME GOOD MEN IS A BETTER WOMAN
6:00 am Thu - UPDATES TO "ANALYSIS" SECTION TOWARD BOTTOM OF POST

Now this is not to imply that single men cannot be good, many of them are. I just feel fortunate and blessed to have such a great woman by my side, who is also a great Mommy to our 18 month old Jayla. Mrs. Foot has given me a lot of freedom the past week to do what needs to be done with this site to make it better for our readers. We love our daughter to pieces, but is has been nice this week while she is visiting Grammy so Mommy and Daddy can get quarter grades done...and I can analyze ad infinitum on the next storm.

Many of you will also be thankful for Mrs. Foot, because she read the site today for the first time in a while…. AND COULDN’T FIND THE FORECAST!! This is a problem. I am embarrassed. If my own wife has trouble finding the weather on the site, then changes are needed. Fast. So we went for a walk, and talked (about other things too, not just the weather) and she recommended some modifications that will make it easier for you (and her) to find what you are looking for. I
t is neat that this new format would come into play on the ONE YEAR ANNIVERSARY to the date this site has been online. That's right, the first broadcast was January 26, 2004. What a year in weather is has been, and will continue to be.

SO HERE IS THE NEW FOOT'S FORECAST FORMAT. It has three simple parts.

1. The straight weather forecast (whatever the hot topic is… a snowstorm, hurricane, etc.) The basic nuts-and-bolts forecast will be issued first for the area under threat of bad weather. No computer model mumbo jumbo, no NAO this and PNA that. Just the weather.

2. The scientific analysis. If you are skeptical of the forecast, have told your friends to start buying snowblowers, or want the scientific basis behind my call, read on to this section. If you are satisfied with the call made in section 1, you can skip section 2 and 3.

3. The philosophy. You understand the weather and the science, but are hungry for more and want the full picture with all it's complicated half-witted analogies and more. Then read on past the analysis to the philosophical background of the forecast.

DISCLAIMER: During megastorm mode, I cannot guarantee this will always be followed, as fatigue, frustration and excessive blogging late at night in advance of major storms may lead to a mangled merger of the 3 sections above, but I will do my best. I strive to put the best safety interests of my readers ahead of weather lingo and ego.

BEFORE WE GO ON TO THE WEATHER… Grading January 22-23 snowstorm/blizzard # 1

Baltimore to PA/MD line: Forecast 8-12 Actual 6-7 Score 6/8 = 75% C

Dundalk, MD (my home): Forecast 8-12 Actual 5 Score 5/8 = 62% D

Southern PA (York Cty.) Forecast 8-12 Actual 6 Score 6/8 = 75% C

Western PA ( 7 Springs) Forecast 12-18 Actual 10 Score 10/12 = 84% B

Philadelphia (airport) Forecast 12-15 Actual 12.6 Score 12.6/12 =105% A*

New York City (JFK) Forecast 10-14 Actual 11.5 Score 11.5/10= 115% B

Boston (Logan) Forecast (initial 6-8” by Sunday night, final call was 30” total)
Actual 22.5 Score 22.5/30 = 75% C

Washington (Dulles) Forecast 4-6” Actual 6” Score 6/4 = 150% E

Overall storm forecast GPA: 2.12 Grade C
If you discover an error in my number, either the forecast amount or actual, let me know.
Explanation of snowfall grading scheme:
All future storms (including today’s micro-blizzard in Mass.) are graded on a single number issued for a specific location where an accurate observation can be verified, such as an airport, or a general trend as reported by colleagues.

I will give a range of expected snowfall, but at the final forecast before the storm begins, the grade is based on the single accumulation number which I will announce. For Boston, I originally called for 4” and should have stuck with that, but revised it to 9” for Logan International based on higher QPF. For the region surrounding the graded location, it is assumed there will be a variance of 2” on either side of the number, but the grade is on that number.

So the Boston area grade is: 5.6 inches reported at Logan as of 1:00 AM Thu / 9" predicted= 62% and that’s an D. So at least I passed. Because despite the higher QPF, the heavier snow portion of te storm moved out quicker, and the real bomb-out did not occur until the Low had moved well-offshore. Some light wraparound snows added another inch overnight.

Wednesday, January 26, 2005

LET'S DO THE TIMEWARP AGAIN...
-Rocky Horror Picture Show

SIGNIFICANT WINTER STORM TO DROP ANOTHER 6 TO 10 INCHES ON EASTERN MASSACHUSETTS TODAY. Boston to easily break it's all time snowiest January. For my powderhounds, it is pure heaven. For powderhaters, it must be a horror show.
Official Foot's Forecast for Logan International... 9 inches.
Based on daytime temp of 25 F, which is a ratio of 15:1 or so and a QPF of .60.
New site updates include excellent US loops of the ETA, GFS, NGM and UKMET. Enjoy! This should help us all stay on top of the next big storm.
I'm not the only one concerned about a potential storm. Accuweather has some graphics illustrating their initial predictions on this late weekend threat. Models are misbehaving so I will take a closer look at the situation tonight.

Tuesday, January 25, 2005


TWO ROADS DIVERGED IN A YELLOW WOOD... AND I TOOK
THE ONE LESS TRAVELED BY, AND THAT HAS MADE ALL
THE DIFFERENCE.

- Robert Frost, from "Stopping By A Woods On A Snowy Evening."

WARNING: Ultra long post. It has to be that way because I must lay the groundwork for the basis of this storm forecast. But if you don't care about the philosophy or the science, and just want the straight talk, then just scroll to the end, I won’t be offended.

The picture above was taken at Seven Springs this past Saturday afternoon as I was skiing in beautiful fresh powder. Looking at this picture, I think to myself… here is a vast field of trees, with many different trails to take. All those trails at first lead to a variety of places, but as I continue along any particular trail, after a while, I reach two possibilities. One, the wrong trail leading me out of bounds and into thick woods. Or…Two, having skied these trails several times before, I have a fairly good sense about which one to take that will eventually connect with others, and ultimately take me to the bottom of the mountain, and my final destination.

But before I overwhelm you with intense scientific analysis, please consider my second analogy.

Earth’s climate and weather all follow a regular pattern. The pattern may not seem very discernible to us mere mortals at times, especially when it is in cycles of 60 or 120 day or 10 years or 200 years. But each weather pattern is an on going highly complex chemical formula, that continually repeats and resolves itself. Recognizing the pattern is more than just looking at the cover of the Da Vinci Code, and saying… “there’s that book!” and then reading the inside flap. To get a real sense of what author was trying to convey in cracking the “Code” you have to immerse yourself in the intricacies of the book and try to pull out some meaning that you and others can understand. Then, when someone asks you, “What’s that book about?” You can give them a reasonable explanation based on your understanding. Usually, when a lot of people read the same book, there are different opinions as to the meaning, but most everyone will come up with some kind of synopsis that is close to the main ideas. Rarely would you have someone give you a synopsis of a book that is totally out of synch with what everyone else read, or you would probably say… “Were you reading the same book that I did?”

And that’s what we have going on with our next big storm. Everyone is reading the same book (the forecast models), and most of the readers (forecasters), are coming up with pretty much the same synopsis of what the book is about (the weekend forecast). Everyone else around them has said, “Since you read the book already, I’ll just take your word for it, and not bother reading, saves me time. Besides, your analysis seems to fit with what everyone else is saying.” But you have read my synopsis of the book, and are thinking, "How is he coming up with that?"

Now relate these two analogies together, so you understand where I am going with this. I have skied for 15 or more years now, and visited a good number of resorts. I have gained an intuition about how trail network is laid out, that I can find my way back to the base lodge easily enough without getting lost. I can just take the standard trails I see everyone else skiing down, and that’ll get me back quickly, little effort. But part of the thrill of skiing is finding those interesting and little known trails, which are clearly marked on the map, but not as well traveled. Such as the picture above… glades, among my favorite type of trail. So I venture through the glades, and I think… “Gosh, this is so pretty here, I wonder why more people don’t come this way?”

And then it hits me… first, I don’t want them to come this way, because too many will spoil the pristine atmosphere at the moment. Second, they aren’t going to come this way regardless, because it looks too different and unfamiliar. It is “off the beaten path” maybe too dangerous, maybe too risky, not sure where it leads, how would I ever get back? That picture was middle of the day, and it appears that not too many people had gone that way since morning. But I took the one less traveled by, and that made all the difference, because I inadvertently found a new route back to the base lodge, one that no one else had skied yet, because it was all fresh powder underneath.

And that my friends, is what I also plan to do with this forecast. I will take the trail less traveled by, because I believe I have enough scientific basis on my side this time, and the confidence to veer away from the traditional routes. My hope is to explain to you the new trail I am taking in a way you'll understand, before everyone else finds it.

ANALYSIS FOR SECOND EAST COAST STORM LATE THIS WEEKEND

Now that you’ve survived the philosophy missive, let’s get on to the real deal.

PART I, TAKE A HAMMER TO THE GFS

(This is the NOAA’s flagship computer model, the Global Forecast System. While is an excellent tool, it is replete with significant errors which have led to debacle after debacle in the big storm arena.)

1. Frustration over wildly vacillating Accuweather 15-day forecasts is a waste of our valuable time because most of those forecasts are tied directly to the GFS database. I’m sure it’ll keep printing out 50 degrees for Boston until the day before the storm.

2. The GFS was the same computer model which consistently predicted that Hurricane Jeanne would GO OUT TO SEA and never hit Florida, let alone in the same place that Frances did. You what really happened.

3. In February 2003, the GFS was unable to initialize in it’s data runs the fact that a gargantuan Arctic high was going to park itself over the East Coast and block forward motion of an intensely moisture laden system coming out of the southwest and Gulf of Mexico. I saved the last Special Weather Statement issued by the Baltimore Washington NWS Office, before I left for the weekend and go to…. Where else? Seven Springs. Would you believe the NWS was still expecting a mix with and changeover to sleet and freezing rain in THAT storm? On Friday, 2/15…forecast highs were in the low 30’s for Sunday at Baltimore. The actual high? 18 F. What was going to be several inches of wet snow at my house (as indicated by the weather service ended up as 23.5 inches, and the rest you all experienced yourselves.

4. How quickly we forget. The GFS was the LAST model to come on board with Blizzard #1, as E.H. in Boston pointed out, and even then just 12 hours before onset of precip. And you’ll remember that’s when most of the NWS offices went berzerk with their Day After Tomorrow-type snowfall predictions. The GFS was consistently advertising that Blizzard #1 would head southeast and out to sea, not to affect New England at all. Did I not say that when we think it will not be as bad, it ends up being much worse than we expect.

5. The GFS has also consistently underestimated the strength of high pressure systems coming southeast from Canada. This is why you have seen forecasted daytime highs and overnight lows for Thursday and Friday dropping all week long for the East Coast. All those 3 and 5 day outlooks? Print them out, put them on your fridge, and keep checking your thermometer to see how accurate they end up being. In fact, Friday morning may be the COLDEST it has been all winter from DC to Maine and everywhere in between. All that cold air is going to filter down the east side of the Appalachians.. all the way to the Carolinas. With a stagnant Arctic air mass dominating the entire Northeast, what scientific basis is there for all that low-level cold air to be suddenly scoured out by Sunday?

These are only a few qualitative example of how this computer model has consistently underperformed it's peers. So why would the NWS continue to follow it, seemingly blindly at times? Politics and power. It would be treason to base a National or Regional forecast solely from a foreign computer modeling program? You don't think certain NWS offices get indirect pressure to lean more favorably on the U.S. model? Then think again about office politics.

PART II : UNDENIABLE EVIDENCE OUR BIG STORM IS COMING

There are several factors crucial in determining whether a big East coastal low will become an all-out-blizzard, a pesky ice storm, or an annoying cold rainstorm. They are…

1. The North Atlantic Oscillation
2. The Arctic Oscillation
3. The Pacific North American Teleconnection
4. Water temperature anomalies off the East Coast

I don’t include the jet streams in that list because the three major upper air phenomena are what drive changes in the jet streams in the first place.

So get a cup of herbal tea, I hear it helps you think clearer, because this is going to be heavy science. But it is worth the read. If you can understand this, then’ll you have also have a clearer picture on where my seemingly out in left field forecasts come from.

1. The North Atlantic Oscillation (The NAO)

What is the NAO? (These are excerpts from a NOAA site I found, and condensed it down for the site.) The North Atlantic Oscillation is defined by differences in pressure between the persistent low over Greenland and Iceland (the Icelandic Low) and the persistent high off the coast of Portugal (the Azores High) During a positive NAO, both systems are stronger than usual. That is, the low has a lower atmospheric pressure and the high has a higher atmospheric pressure. During the negative phase of the NAO, both systems are weaker, lowering the difference in pressure between them. (end of NOAA summary, found here)

You know that a tight isobar gradient indicates strong winds, as the pressure difference between the high and low are very large, thus intense storms often wind up and become these highly compact systems. A high pressure system, by contrast, is a large, expansive dome of air. When the NAO goes negative, it means that the Icelandic Low and the Azores High both become larger and more spread out, as the pressure differences between them are not as much. This in turn allows for the Icelandic Low, which is naturally much more closer to the North American coast, to influence the weather of that coast. This diagram shows what happens in a negative NAO.. as the Icelandic low, with it’s counter-clockwise rotation, moves closer to the U.S. East Coast. By doing this, it begins to cause what forecasting term “blocking” in that it interferes with the normal jet stream induced flow of storms, as well as re-direct the movement of Arctic highs coming down from Canada. The highs get shunted into the Northeast U.S., and any southern stream storms coming out of the Gulf of Mexico, usually loaded with moisture, get funneled into the path of those Arctic highs.

The Negative NAO signal. Look at the
current NAO chart yourself. Look what happened right around the 23rd…. the NAO flipped from strongly positive to mildly negative. NWS forecasters do know about this stuff, it’s their data. Perhaps they forgot to check it, I don’t know. But I can tell you there is a very strong correlation between changes in the NAO and the occurrence of big storms along the East Coast. Boston… when was your last storm since November? Look at the NAO chart. Does that verify? Notice how the positive NAO in December corresponds to the much-above normal temperatures we all experienced throughout the Northeast last month? Then look at January. Started out warm, and the NAO just kept dropping and dropping as the month progressed, eventually flipping to negative just last weekend. What followed immediately after the flip? A little Alberta clipper that kept growing until it became one of the top 5 biggest storms in New England history. Knowing what you do now about the NAO, don't listen to any forecaster who blames the bad calls on the fact that the storm just "came out of the blue. " Nonsense, their homework went into the blue.

Where is the NAO headed? It is already trending STRONGLY negative and forecasted to continue that over the next two weeks. View for yourself NOAA’s 7, 10 and 14 day projections. I think local NWS offices are for some reason discounting that the NAO signal is already significantly OFF the forecasted value. Look very closely at the second chart, see that black line? That is the current NAO "value" based on observations. Notice how far off that line is from the forecast for where it is supposed to be. It may not look like a big difference to you, but in forecasting lore, the value was supposed to be about a .75 deviation to positive. Instead, as of today, it is over 1.5 deviations to NEGATIVE. That's the equivalent of forecasting 7 inches of snow, and the result is 22 instead! Does that sound familiar, Boston?

Now, look at the second, third and fourth charts... what is the overall trend for the short term to about January 27? Is NAO forecasted to be... negative, neutral or positive?

The correct answer is...FORECASTED TO BE POSITIVE for the immediate term. That forecast was made a week or so ago.

THIS IS WHY YOU SEE A "WARMUP" IN YOUR WEEKEND FORECASTS. The GFS INITIALIZES THE NAO FORECAST IN IT'S DATA RUNS, BUT SOMEHOW SEEMS TO DISCOUNT THE NAO OBSERVATIONS. Please forgive the caps, I am not shouting, just trying to strongly emphasize that we have found the smoking gun, have we not? The bias toward a positive NAO is in direct contradiction to current observations, so the NWS offices have to manually adjust their temperature projection because the GFS has an above-normal temperature bias because of the positive NAO signal.

What will probably happen is once enough observational data comes through between now and Friday, the GFS will start to change it's tune, and back off the warm trend. Then slowly, you'll notice the NWS forecasts start to ever so slightly trend colder, first temps will nudge down a degree, then the precip type will begin to shift toward a more snowy solution. And finally forecast discussions will begin reflecting this in the next few days.

I will discuss these three factors in more detail with Wednesday evening's post.

2. The Arctic Oscillation

3. The Pacific North American Teleconnection

4. Water temperature anomalies off the East Coast

PART III: THREE STORM SCENARIOS

This is the three most likely situations that will occur late in the weekend to early next week, as some computer models have slowed the potential system down quite a bit.

Storm A...All washes away. The cold air this weekend is quickly replaced by warm air advection from southwest flow of the moderating high pressure. A storm does form in the east side wrinkles of this high, but cuts up through the Chesapeake and into the St. Lawrence River Valley by Sunday night, bringing widespread moderate to heavy rain and the potential for significant flooding in snowpack areas of New England and the Northeast. Mr. Foot wears a big grocery bag on his head and posts a picture on the website for all to see.

Storm B...Big trees falling down everywhere. The cold air this weekend remains firmly in place, filtering all the way to South Carolina. A low pressure in the Gulf moves off the Carolina coast, and over-running moisture falls through the surface layer cold dome. With 2-3 inches of liquid available, this becomes a major to nearly catastrophic ice storm for the Carolinas and Southeast Virginia. The Northeast is spared any serious impacts other than a few inches of wet, sloppy snow and some tail end freezing rain as the storm departs east. Mr. Foot wears half a grocery bag.

Storm C...Can you dig it? (even if there's 2 more feet of it?). An unusual confluence of events results in a strongly Negative NAO signal which correlates with the arrival of an large Arctic high into New England on Thursday. The high moves south and expands, temperatures are notably colder than originally forecasted. At the same time, an active southern jet stream sends a developing low pressure system through the southern Ohio Valley, which eventually redevelops off the Carolina coast. The high drifts off the coast, and becomes entrenched due to it's proximity to the Icelandic Low. The resulting blocking of the storm's movement enables the low and high in conjuction to tap warm Atlantic waters, feeding tremendous moisture into the cold dome of air over the Northeast for 2 or more days. The result is a historic paralyzing blizzard with snowfall amounts of 12 to 24 inches for all major cities from Washington to Boston, and 24 to 36 inches in interior sections of Pennsylvania, Maryland, New York and New England.

Mr. Foot mails a grocery bag to every NWS office on the East Coast with his web address printed on the side.

Only time will tell what really happens, but by Thursday we should have a better sense of which scenario is likely to play out. Of course, you know I am still leaning on Storm C.

Brief update tomorrow morning, followed by fine tuning of the three scenarios tomorrow night and continuation of Part II.