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.


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