Tuesday, December 13, 2005
Extremely Cold December Marches On
Matt Ross @ 1:00 AM
Forecast
Today will be sunny, but temperatures will have a hard time rising. Afternoon highs will top out in the low 30s, some 15 degrees below our normal high of 48 degrees for this time of year. So far we are running almost 8 degrees below average for December, with little to indicate a warmup in the near future. Wednesday will be much of the same with some increasing clouds in advance of our next precipitation maker. More on that below.December Snow Notes
I have often emphasized that big snow events in DC are rare. More often than not, things can and do go wrong. Illustrative of this is that we have received nineteen straight measurable snow events at National Airport of less than 6". In fact our last event of more than 6" was the President's Day storm in February of 2003. I can tell you from experience forecasting many of these events, that most of them underperformed the expectations 2-3 days in advance as indicated by weather models. We are not an area where it can snow a lot even when certain key ingredients are missing. I think one thing you will get at CapitalWeather this winter is lack of hype, especially several days before an event. Even though most of us love snow, our years of dashed hopes and underperforming storms has helped cautious skepticism trump our excitement over potential. As you monitor different forecasts this winter for our area, I would view most forecasts for large snowfalls(6"+) outside of 72 hours with extreme skepticism. Most of the time they will be wrong.
Although it is early, and as Jason mentioned yesterday we are ahead of pace for snow this season, current seasonal snowfall totals are falling pretty well in line with climatology with respect to each other. Here are the current standings for the I-95 corridor through yesterday:
Portland, ME: 16.4"
Boston: 11.6"
New York: 9.3"
Philadelphia: 6.8"
Baltimore(BWI): 6.2"
Dulles Airport: 4.9"
National Airport: 4.6"
Richmond: 4.4"
Note that we have already exceeded the snowfall for the entire season for 1949-50, 1972-73, 1975-76, 1980-81, 1997-98, 2001-02. Not too shabby.
Downtown Boston gets pummeled with blizzard conditions last Friday afternoon. Whiteout conditions and reports of frequent thunder and lightning were commonplace in Southern New England as a powerful storm that gave us several inches charged rapidly up the coast. Courtesy of Jeff Reid.
Next Chance of Snow: Thursday, December 15th- Friday, December 16th
Probability: 50%
Potential Impact:
Commentary: We will be under the influence of a very strong area of high pressure which will keep our temperatures well below normal as a system approaches our area from the Gulf of Mexico and another system heads towards the Great Lakes. Current solutions are in fairly decent agreement that we will start as snow or a snow/sleet mix early Thursday morning around dawn. There is equally decent agreement that we will switch over to something other than snow fairly quickly as warm air penetrates the upper levels of the atmosphere due to rapidly retreating high pressure and a low pressure track that is slightly inland. The details are somewhat sketchy at this point, particularly with respect to how quickly cold air will retreat at the surface. Right now my best guess is that the entire area will start as some light snow or snow/sleet mix around rush hour Thursday morning with some small accumulation possible. This should change to a mixture of sleet, freezing rain and rain starting mid-morning in the southeast suburbs and moving west and northwest through the area into the western suburbs by mid to late afternoon. Most of the area should be all rain by late afternoon on Thursday and stay that way until the precipitation stops sometime after midnight Thursday night. Surface temperatures will be critical in determining how much of an impact this system will have. While I do not currently see this as a high impact event, there will likely be some problems on the roads in the typical areas north and west of town and based on the timing, I would expect widespread delays and cancellations. Here is a statement issued by the National Weather Service regarding the event. Stay tuned as the details really need to be ironed out as always.
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