Snow Obsessive-Compulsive Disorder Outbreak Expected in DC Area

For related posts, see:

• Record Snow
• Washington DC Weather Records
• Winter Weather

Major Winter Storm of Hysterical Proportions?

Feb. 3, Midnight Update: The GFS model continues to be consistent, a little drier (more realistic), a little less warm than the NAM. Although precipitation amounts are still very high, the rain/snow line is still a concern for snowfall amounts, especially in the immediate Washington/Baltimore area.

Feb. 3, 9:35 PM Update: The evening (00Z) NAM model has reached 60 hours within the last few minutes. There are no surprises, although the forecast storm position for Saturday morning is closer to the coast. This brings in more warm air and increases the chances for precipitation mixing or changing to rain.

Feb. 3, 5 PM Update: The afternoon model run, with 72-hour results being posted just within the last few minutes, is confirming the general story of heavy precipitation, mainly snow, beginning during the day on Friday and extending into Saturday. The main difference is that precipitation amounts have increased from earlier runs.

Feb. 3, 4 PM Update: The Washington/Baltimore local forecast discussion has been updated. As indicated here earlier, mixing or changeover to rain will be a major issue, but some very heavy snow amounts are still likely.

BY MIDDAY FRI...MODERATE-HEAVY PRECIP WILL BE PUSHING ACROSS THE ERN
SEABOARD AND INTO THE MID ATLC. ENOUGH COLD AIR WILL BE IN PLACE /E
OF I-95/ FOR AN ALL-SNOW P-TYPE /POSSIBLY A BRIEF PERIOD OF A RAIN-
SNOW-SLEET MIX AT ONSET/. ALONG AND E OF I-95 WILL CERTAINLY BE THE
MIX LINE FOR MUCH OF THE DAY...W/ A CHANCE OF A SNOW CHANGEOVER
LATER IN THE EVENING-OVERNIGHT AS A SFC LOW STRENGTHENS OFF THE
COAST OF CAPE HATTERAS AND PULLS SOME OF THE COLDER AIR BACK SWD. AS
THIS LOW STRENGTHENS...MUCH LIKE THE DEC STORM...WINDS WILL
STRENGTHEN OVER THE BAY AND COASTAL REGIONS /NEARING GALE WARNING
FROM SAT AFTN-EARLY SUN/. BACK TO THE WEST...SNOW WILL CONTINUE OVER
THE REGION AND BE ESPECIALLY HEAVY AND CONTINUOUS LATE FRI INTO
EARLY SAT. EVEN AS THE SFC LOW TAKES A BULK OF THE SYSTEM OFF THE
MID ATLC COAST SAT MORNING...SNOW WILL CONTINUE ALL THE WAY BACK
INTO THE OHIO VLY /HEAVIEST EAST OF THE APLCNS/. ANOTHER ROUND OF
LIGHT-MODERATE SNOW WILL CONTINUE THRU MUCH OF THE DAY FOR THIS
REGION ASSOCIATED W/ THE PASSING UPPER TROF AXIS. 

Note that the first reference to p-type (precipitation) is undoubtedly a typo and should refer to all or mostly snow west of I-95, rather than east.

Feb. 3 PM Update: At 2:45, the National Weather Service issued a Winter Storm Watch for the Washington, DC/Baltimore area and much of adjoining central Maryland and northern Virginia for Friday and Saturday, Feb. 5-6:

WINTER STORM WATCH IN EFFECT FROM FRIDAY MORNING THROUGH
SATURDAY EVENING...

THE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA HAS ISSUED A
WINTER STORM WATCH...WHICH IS IN EFFECT FROM FRIDAY MORNING
THROUGH SATURDAY EVENING.

* PRECIPITATION TYPE...SNOW.

* ACCUMULATIONS...THIS STORM IS LIKELY TO PRODUCE 12 OR MORE
 INCHES OF SNOW IN THE WATCH AREA...WITH A GOOD CHANCE FOR
 LOCALIZED AMOUNTS OVER 20 INCHES.

* TIMING...SNOW IS EXPECTED TO BEGIN LATE MORNING
 FRIDAY...CONTINUING THROUGH SATURDAY EVENING.

* TEMPERATURES...HIGHS IN THE LOWER TO MID 30S FRIDAY. FRIDAY
 NIGHT AND SATURDAY...TEMPERATURES WILL BE 25 TO 30 DEGREES. 

Feb. 3 Noon Update: The latest model run, posted within the last hour, continues to show a major storm off the Mid Atlantic coast by Saturday afternoon. The timing has accelerated a bit, however, and the precipitation amounts, although still heavy, are a little lower.

The storm evolution is now also within range of the higher-resolution NAM model. In general, it tells a similar tale, but with some subtle differences. The storm is slower, wetter, but also a little warmer.

The bottom line at this point approaching 48 hours to the onset of the event:

• A major storm is extremely likely to develop
• Precipitation will probably be heavy
• Enough cold air will be in place for the majority to be snow in parts of the Mid Atlantic area

So what could possibly go wrong? Just ask the crack chefs at Momma Nature's Weather Grill why they keep such a large array of mops and other cleaning tools in their kitchen. The major risk to this forecast is the potential mixing or changeover of precipitation to rain for a while, especially as the storm is initially strengthening off the coast.

Image (click to enlarge): Computer model forecast for 7 am Saturday, Feb. 6, shows a strong storm moving away from the Mid Atlantic Coast. Precipitation amounts in the Washington area would be in the range of 3-6" of snow in the previous 6 hours, with larger amounts earlier. Implied temperatures would be cold enough for snow southward through nearly all of Virginia.

Feb. 2 Evening Update: Despite some amateurs flaunting their crystal balls, as of 9:16 pm, the National Weather Service is prudently reiterating their guidance:

THE FORECAST REFLECTING A GOOD CONSENSUS W/ LONG RANGE GUIDANCE...
WHICH POINTS TOWARD A FAIRLY SIMILAR SET-UP FROM THE LATE DEC STORM
/AT LEAST IN MID LEVEL DYNAMICS UPPER VORT MAX WELL WEST OF THE
STRENGTHENING SFC LOW OFF CAPE HATTERAS-VA TIDEWATER/. STILL TOO
EARLY TO FOCUS ON AREAS-ACCUMULATION...THO POPS HAVE BEEN RAISED
INTO CATEGORICAL RANGE FOR LATE FRI-THRU EARLY SAT. ALSO...THIS
SYSTEM APPEARS TO HAVE MORE WARM AIR WRAPPED INTO IT. ENOUGH COLD
AIR WILL BE ASSOCIATED W/ THE APPROACHING UPPER LOW ON FRI TO BE
MAINLY ALL-SNOW FOR THE ENTIRE CWA /OUTSIDE OF LOWER SRN MD-NEAR
BAY AREAS WHICH WOULD BE MORE OF A RAIN-SNOW MIX/. 

Feb. 2 PM Update: This afternoon's view of Saturday's map shows a distinct jog to the north in the storm position, even in relation to the model run made just 6 hours earlier from this morning's data. At the 96-hour range, the general picture of a classic East Coast storm is coming into focus, but even a 72-hour forecast has an average error in storm location of about 175 miles, which makes a big difference in the weather at any particular location. For what it's worth, however, (and it can't be taken literally) the model is projecting an area of 1.5"+ of precipitation from the Carolinas northward through Virginia and into the southern two-thirds of Maryland. From about a line from DC to Baltimore northward, much of this would be frozen, so snow amounts of a foot or more would not be out of the question in some places. Assigning specific numbers, even in probabilistic terms, however, at this point is pure hype-casting.

Feb. 1 Update: This just in: Model forecasts at the range of 5 or 6 days can have errors. Here's this afternoon's version of a forecast for the same time on Saturday. Notice any differences?

• The Hudson Bay high is not as cold and is centered further west.
• The low is still strong but not as intense.
• The heaviest precipitation is further south.

Some of the differences are the result of faster timing. Other models have different ideas. So far, the indications are that the odds for snow are more favorable south of the Mason-Dixon line than north. At least some fanatics are likely to be disappointed. Back to our regular programming.

Original post:
After a week of hyperventilating over the prospect of what turned out to be 4-6" of mostly air in the Washington metro area, snow obsessive-compulsive disorder victims should brace themselves for the coming week. It's waaay too early to assign percentages, as a certain blog (they know who they are) does to pimp out their eyeball count, but the models are hinting at the possibility of a major east-coast storm for next weekend, Feb. 5-6.

The latest run this afternoon of the GFS, the primary U.S. computer model, shows a pool of extremely cold air anchored over Hudson Bay and a strong low-pressure area developing off the southeast U.S. coast (click image to enlarge). The 6-day forecast, for 1 pm on Saturday, shows heavy precipitation (as much as 1" in 6 hours, roughly 10" of snow) from near Washington, DC southeast to Tidewater Virginia. Temperatures are indicated to be cold enough for snow as far south as central Virginia and eastward to the middle of the Maryland Eastern Shore. In short, all the ingredients from Momma Nature's Weather Grill cookbook.