Wednesday, February 7, 2007

"I KEEP WORKIN' MY WAY BACK TO YOU, BABE.."
-Stephen Gately and the Detroit Spinners,
in a 1980 remake of the 1965 original by Frankie Valli and the Four Seasons

ALERT FOR MY BUSY READERS:
SCROLL BELOW "PICTURES AND MEMORIES" SECTION TO LOCATE
FORECAST & ANALYSIS OF NEXT WEEK'S VALENTINE'S DAY STORM

TRULY A STORM OF HISTORIC PORPORTIONS!

For East Coast powderhounds, the President's Weekend Blizzard of 2003 was one of the all-time top storms by which most future ones will be measured, including the upcoming Valentine's Day Bonanza of 2007. Before I get into the analysis of our upcoming complicated storm (or series of storms), a few memories to whet your appetite: First is the accumulation total in my Dundalk, MD backyard the morning that snow finally ended.

NOW THERE'S A SITE YOU DON'T OFTEN SEE!

Second is one of my favorite pictures of the storm..the front doors of our school. It represents the incredibly herculean task that had to be undertaken by our hard-working grounds and facilities staff in Baltimore County to clear and prepare 130+ school buildings, offices, parking lots and untold miles of sidewalks. Working in round-the-clock shifts, it still took 5 days to get the county-wide system ready, and what an incredible week that was for those of us who did NOT have snowblowers.

AH YES, MEGA SNOW TO DIG

The powderhound in me was too excited at having a forecast perfectly verify (I told colleagues at school 5 days prior to the storm there'd be 18-24 inches in Dundalk) and running around taking pictures I didn't bother to keep up with clearing the snow. Thus all time time I was going to spend grading over that week was sapped by shoveling. Not this time my friend. This time I know what's coming, I understand the impacts, and I will be ready.


VALENTINE'S DAY 2007 STORM ANALYSIS

For those new to this site, please allow a primer on my forecasting rules for big storms:
1. I issue an early projection of snowfall totals based on the extrapolated computer data. Early meaning I come out with numbers sometimes 5 days to a week before the storm.

2. The early projections are refined up until 24 hours prior to onset in affected areas

3. At 24 hours out, I issue what I call "Storm Grade Amounts" which are not altered. This is the accountability system of this website. Instead of a range, I will peg a specific accumulation of snow for certain locations and others by request from readers.


4. At conclusion of the storm, the readers and I use authentic and valid snowfall observations from National Weather Service field offices and spotters. We assign a letter grade to the to the accumulation forecast (A-B-C-D-E) according to deviation from the actual amount observed. We follow traditional academic percentages, 90%= A, and so on. Example:
"Martinsburg, West Virginia: 6 inches." If that location actually receives 8 inches, it is deviation of 2, thus graded as 8 / 6 which although is 125%, is not considered an A but is actually a C because the final number deviated 25% from the expected value.

5. In large, widespread storms a final Grade Point Average is determined as a method of measuring the overall accuracy of the accumulation forecast. Here's a link back to how I fared on a February snowfall forecast last year.

OVERVIEW OF STORM DYNAMICS AS IT AFFECTS PUBLIC PERCEPTION
It is now fully clear to most meteorologists across the Eastern U.S., whether private or public, professional or amateur, that one or more significant winter storm(s) will be developing in the time period February 12-15. Primary impacts will be felt from the Southern Plains to the Southeast and Mid-Atlantic states. You should be warned that this storm, like many others, will present for many weather serveice an evolving and complicated forecast challenge unlike standard "cookie-cutter" snowstorms of the past. As more computer model data becomes available, it is being realized this storm may actually come in a series of impulses over 2-3 days, each requiring a different set of analyses and resulting in varying types of winter precipitation. This style of storm will no doubt create considerable anxiety among the public as it may be difficult for public and private forecasters to nail down exact amounts and locations until very late in the period prior to onset. I account for this uncertainty with the framework I have established for storm forecasting as explained above.

1. MY EARLY CALL FOR SNOW ACCUMULATIONS
No changes to my initial call from Tuesday 2-6. I project 10 to 20 inches of snow in the central Mid-Atlantic, with the northern boundary of the heavy snow area just north of Philadelphia. This would include the southern I-95 corridor from PHL to Richmond, as well as the entire Baltimore and DC Metro areas and their corresponding interior counties. Delmarva and southern New Jersey will be tricky as there could be some mixing and rain, so amounts should be lower. The time frame for this will be starting possibly as early as overnight Monday continuing into Wednesday, perhaps ending by 12 noon or in the midafternoon. In my notes and analysis of Friday 1/26, I originally scoped out a total 12-18" snowfall for the February 12-16 period for Baltimore, so this is still within those parameters. The final call will be made 24 hours prior to onset where I will post specific amounts.

2. WHAT DO COMPUTER MODELS SHOW?
Well it's a good thing you asked, because I just happen to have a few maps about this topic. First is the current GFS 60-hour total liquid equivalent projections for Wednesday Feb 14. That means the total amount of liquid available in the atmosphere ending on that day. Weather forecasters call this QPF (quantitative precipitation forecast). You can clearly see how the central Mid-Atlantic is in line to receive anywhere from 1.0 to 2.0 inches of liquid. Of course this is going to change many times in the next few days, but the general trend is there, a lot of moisture over a large portion of the Mid-Atlantic.

Feb Storm 2E

What's really interesting is that the European model (the ECMWF) and the U.S. model (the GFS) have been generally showing a similar setup for next Tuesday night into Wednesday morning. In fact there's considerable agreement among a number of computer models about this storm, which is unusual to see 7 days prior to the event. If I recall correctly, a similar situation occured with the March 1993 Superstorm (although this will not be anywhere near the intensity of that one.)

Feb Storm 2C

The GFS model runs have been somewhat inconsistent the past 24 hours so I will post an image of the latest printout that's most representative of the general trend. What I don't like about the map above as it relates to my forecast is the potential for this storm to get squeezed out to sea by the strong high pressure. I could easily see the scenario where the 1048 high sinks south and keeps the heavy precip even below DC, so Richmond and the Carolinas get hammered and the central Mid-Atlantic are left dry and whimpering. In the President's Day Storm of 2003 that high was positioned farther to the east and a large chunk of it nosed out into the Atlantic. This in effect caused "overrunning" as copious amounts of moisture "ran over" and into the cold dry air, enhancing the liquid-to-snow ratios which produced very significant accumulations from the Mid-Atlantic well into New England.

3. WHAT ARE PROFESSIONAL FORECASTERS SAYING?
A number of government forecasting agencies have picked up on this and have started the discussion in their long range outlooks. To be fair, I've also been following the research of some private forecasting agencies, including AccuWeather and other , who have been alluded to the potential of a major event in mid February for some time now. In no way do I claim to be the first person to call for a big snowstorm. There are many others who already have that prize. Here's a roundup of statements from NWS offices and agencies on Wed Feb 7. Please note bold and italics emphasis is mine to highlight differences in their analysis, and also note the NWS routinely issues statements in upper case.

The National Centers for Environmental Prediction's US Hazards Assessment: Feb 9-20

The generally dry pattern across the CONUS is expected to change during this Assessment period. Multiple rounds of rain are forecast to impact northern California, leading to the potential for flooding. This moisture could then cause heavy snow in parts of the Rockies as it continues to move eastward. A storm forecast during the 6-10 day period could bring severe weather to the Gulf Coast, and the first chance this winter of heavy snow to the major cities along the East Coast. Heavy lake-effect snow is also possible as all the Lakes except Erie remain relatively warm. Temperatures are expected to remain cold in the East, but anomalously low wind chills, like the ones recently observed, are not expected at this time.

The Hydrometeorological Prediction Center's Extended Range Discussion

(WE) PREFERRED (A) BLEND THAT LEANS MORE TOWARD THE NCEP MEAN THAN THE ECMWF BY DAYS 6-7 TUE-WED ACCOUNTS FOR THIS UNCERTAINTY AND MAINTAINS REASONABLE CONTINUITY WITH YDAYS FCST...WHILE LEAVING A DOOR OPEN FOR A LESS SUPPRESSED LOW/COASTALSYSTEM AND ASSOCIATED POTENTIAL THREAT FOR ORGANIZED WINTER PCPNDEVELOPMENT FOR THE SRN/SERN US AND MID-ATLC.


The Baltimore/Washington (Sterling, VA) National Weather Service Office:

FORECAST RATIONALE...WITH A QUIET MEDIUM RANGE...FOCUS WAS ON A POSSIBLE SNOW STORM EARLY NEXT WEEK. GLOBAL MODELS INDICATE THE SOUTHERN STREAM PACIFIC JET LEFT EXIT REGION COUPLES WITH THE RIGHT ENTRANCE REGION OF THE NORTHERN STREAM JET ACROSS THE TENNESSEE VALLEY AND MID ATLANTIC. THERE ARE TIMING DIFFERENCES BETWEEN THE 12Z GFS/CANADIAN AND 00Z UKMET/EUROPEAN. HOWEVER IT IS NOTEWORTHY THAT EACH MODEL HAS A SYSTEM IMPACTING THE REGION DURING THE PERIOD...AND SOME OF THE GLOBAL MODELS HAVE SHOWN THIS SYSTEM FOR SEVERAL RUNS. 12Z GFS PRODUCED A HALF INCH (NORTH) AND CLOSE TO TWO INCHES (SOUTH) OF LIQUID EQUIVALENT MONDAY NIGHT THROUGH TUESDAY. THE ARRIVAL OF THE SOUTHERN STREAM PACIFIC JET IS LIKELY THE RESULT OF A LARGE SCALE PATTERN CHANGE. MOST SIGNIFICANT WEATHER COMES DURING THESE LARGE SCALE PATTERN CHANGES. GIVEN THE ABOVE...HAVE GONE WITH 50 POPS (JUST UNDER LIKELY) ENTERING THE REGION MONDAY NIGHT AND FOR TUESDAY (SINCE AT THIS RANGE THERE ARE UNCERTAINTIES THAT NEED TO PLAY OUT SUCH AS TIMING...DURATION AND TRACK). MENTION WILL ALSO REMAIN IN THE HAZARDOUS WEATHER OUTLOOK (WBCHWOLWX). WHILE TIMING AND DURATION (AND POSSIBLY TRACK) WILL CHANGE BETWEEN NOW AND TUESDAY...THERE IS A GOOD DEAL OF SUPPORT TO GIVE CREDENCE TO THIS SYSTEM.


The Philadelphia (Mount Holly, NJ) National Weather Service Office:

LONG TERM /FRIDAY THROUGH TUESDAY/...WITH THE 00Z RUN LESS PESSIMISTIC FOR SATURDAY, WE CONTINUED THE 20 POP FOR SNOW SHOWERS, BUT MANUALLY ADDED THE WORDS FOR THE OTHERWISE INVISIBLE SLIGHT CHANCE IN THE TEXT FORECASTS FOR THE NORTHWESTERN ZONES ONLY. THE LESS SAID ABOUT THE NOR'EASTER OF 2007, IF YOU BELIEVE THE 240 HOUR PROG, THE BETTER. WERE THIS TO VERIFY, IT COULD BE A POTENT STORM. LETS SEE HOW MANY TIMES THIS CHANGES BETWEEN NOW AND 16 FEB; ALSO, LET'S SEE HOW THE 12Z RUN APPROACHES IT'S SOLUTION AND COMPARE IT TO THE 00Z RUN.



The Richmond, VA (Wakefield) National Weather Service Office:

BY LATE WKND/EARLY NEXT WK...HIGH PRESSURE BUILDS INTO SRN ONTARIO FROM THE NW TERRITORIES. MEANWHILE...UPR LVL JET INTENSIFIES OFF THE COAST OF BAJA AS DIFFLUENT FLOW DVLPS OVER THE SRN PLAINS. THIS WILL MAKE FOR LATTER SHRTWVS (MID-LATE NEXT WK) EJECTING OUT OF THE FOUR CORNERS REGION TO INTENSIFY ALONG THE GULF COAST INTO THE SOUTHEASTERN US. SOME OF THESE SHRTWVS WILL HAVE THE POTENTIAL AS THEY INTENSIFY TO TRACK FURTHER TO THE NORTHEAST...AND POSSIBLY EFFECT THE CWA. IT IS WAY TOO EARLY TO TELL ACTUAL STRENGTH/TRACK OF SRN STREAM SHRTWVS AND THE OVERALL CHCS FOR PRECIP NEXT WK. HOWEVER...THE POSITION OF THE ONTARIO HIGH PRESSURE SYSTEM COULD LEAD TO COLD AIR DAMMING SITUATIONS AHEAD OF ANY SHRTWVS THAT EFFECT US.

4. WHAT ARE CLIMATE TELECONNECTIONS INDICATING?
I'm working on that graphic and will post it later with the GFS. The general idea is that the NAO (North Atlantic Oscillation) is trending neutral to slightly positive, the AO (Arctic Oscillation) is trending generally negative, and the PNA (Pacific North American Index) is in positive territory. This is not the completely perfect setup I would want for a big snowstorm, but it's acceptable for now. There are many other climate indicators as well that play into all significant weather pattern changes, including the Southern Oscillation Index, the Eastern Pacific Oscillation as well as Global Sea Surface temperature anomalies, especially in the Gulf of Mexico, the East Pacific and the U.S. East Coast. Each of these indices or indicators plays a central role in the final outcome of a storm, and I will do my best to succinctly explain the basics. Since this set of data does not change as frequently as a 6-hour interval of most computer models, I have time to assemble my information and present at later time.

If you wish to contribute to our rousing and respectful discussion of this storm, please do so via the comments feature, which upon activating will prompt you to create a free, simple, no risk account with blogger. I promise that doing this does not result in you receiving spam, unwanted pop-ups or anything else or the type, nor are you asked to reveal any compromising personal data in signing up. We look forward to hearing your thoughts on this storm and many others to come. If you enjoy following and preparing for big storms, then this could be your lucky week, as those of us who are known as "powderhounds" understand the headline: We keep working our way back to the next big storm in the hopes it will be as good as ones of the past.

13 comments:

terpguy said...
This comment has been removed by the author.
terpguy said...

(sorry for the delete too many mis-spellings!)

OK- let's sit back and watch this puppy develop.

This is going to be exciting.

FWIW, DT at WxRisk is calling for a 12 Feb onset.

Let's see: HPC, NOAA, Wxunderground, weather.cod.edu, WxRisk, EUSWx, and of course, Foot's Forecast all "favorited" and ready to view!

Bring it on!

Mr. Foot said...

(big sigh)

That post I somehow deleted somehow reappeared around 7 PM, so by the good grace of my wife and the fact we are not doing a bath tonight, I merged the 2 posts together and now my the prelim analysis is out there for your perusal.

Oh Mr. Terp..tell DT he's gotta back that storm off a day, we have to finish reports in school and get the Greenhouse ready. Feb 12 is too early.

Andy, Southern York County PA said...

What is snow?

Ben said...

...baby don't freeze me, don't freeze me, no more :-)

I would love to have my first snow day of University here in DC! Bring it!

Anonymous said...

Yikes... I hope that it waits until I bring my group home safely from Orlando!! I will gladly borrow a friends laptop on the trip and give you the highs and lows... ::::::running and hiding::::

terpguy said...

Oh Mr. Terp..tell DT he's gotta back that storm off a day, we have to finish reports in school and get the Greenhouse ready. Feb 12 is too early.

It's cool...he's 0 for this winter. But, he DOES have it starting late PM.....

Kim said...

This is my first time on this site and I think it's great!! Finally...someone we can rely on. Yippee!!! How exciting! I am soooooo looking forward to getting blitzed by this storm. I think I love snow more than my kids!!

Frank said...

I hope that snow sheild can reach me up here in cnj. I am afraid it is going to get supressed enough so that I may see a few inches on the high side, or nothing at all.

Mr. Foot said...

Welcome Kim to the powderhound club. You'll find an entertaining and highly educated group of snow enthusiasts here. They and I have been talking back and forth so much the past 3 years we're practically family by now.

Except of course for Julee, she doesn't talk to me anymore :-( my forecasts just aren't good enough for those high standard country folks in the Hereford Zone. (teardrop)

In all seriousness, we have a great time with this site and it's out own private (actually public) little weather community. Sometimes the highlight of my day is to dash in the door and see what interesting and fun things everyone has said during the day when we're in storm mode.

And this upcoming 7-10 day period will be just as fun to watch and read.

Andy, Southern York County PA said...

Well these forecast insights are good enough for us low standard country folks way up here. So bring em on.

Mr. Foot said...

Hey andy meant to ask what would be the town nearest you so I can add you to the Foot's Forecast Friends List?

You should read the latest NCEP discussions, makesyour eyes water. Looking like a honkin' good snowstorm for all of us.

terpguy said...

I didn't want to say anything, as I still consider my self a rookie, but I was getting a feeling that there might be two systems coming.

Ohboyohboyohboyohboy.....