New round of snow may slow Wednesday morning commute

For the second straight morning Wednesday, snow is likely to fall in the D.C. area.  This morning’s snow didn’t stick on roads for the most part, but, with colder temperatures and an earlier start, snow tomorrow morning has a much better chance to coat the roads and cause slick travel.

Simulated radar from high resolution NAM model at 5 a.m., showing moderate snow potentially over the region (WeatherBell.com, click to enlarge)
Simulated radar from high resolution NAM model at 5 a.m., showing moderate snow potentially over the region (WeatherBell.com, click to enlarge)

Key points:

  • Snow starts roughly between 2 and 4 a.m., west to east, and ends 8 to 10 a.m., west to east
  • The steadiest snow probably falls between 4 and 8 a.m.; so the first half of rush hour is probably worse than the second half for travel
  • As snow will start when it’s still dark (not having to confront strong late February sun) with temperatures from 25-30, it should stick on most surfaces.
  • Generally, 1-2 inches of snow is most likely, but locally heavier amounts of 2-4 inches could occur if heavy bands develop.  Alternatively, less than 1 inch could be more common if a steadier area of snow fails to materialize.
  • After the snow ends by mid-morning, temperatures recover into the mid-30s or so, and the late February sun should melt the snow quickly, much like today .

Capital Weather Gang snow accumulation map, issued 4 p.m. Tuesday.

SchoolCast


1.5 apples: Good (better than 50/50) chance of a delay, 25 percent chance school closes. Do your homework.

FedCast


2 domes: 50-50 chance of a delay and/or unscheduled leave option.

Technical discussion

The setup for tomorrow’s fast-moving snow event is very similar to today’s. Model actually suggest a slightly stronger system with colder air and more moisture. In its discussion, the National Weather Service writes:

ATMOSPHERE SHOULD BE COLDER. PLUS…EARLIER SNOW HAS LEFT DEWPOINTS HIGHER WHICH MEANS WE’RE CLOSER TO SATURATION.SINCE FACTORS BETTER THAN EARLIER TODAY WHEN ACCUMULATING SNOW REALIZED…DON’T SEE WHY WE CANT AT LEAST DUPLICATE THOSE RESULTS. THE ONLY DIFFERENCE WOULD BE THE SCOPE OF JET DYNAMICS…WHICH CAN PRODUCE MORE THAN PROGGED…ALSO SHOULD YIELD A WIDER SWATH OF PRECIPITATION.

Overall, the available ingredients favor a higher impact event than this morning over a wider area. Having said that, today a band of heavy snow – by chance – just happened to set up right over D.C. and its southern suburbs. We can’t say with confidence such a scenario will repeat. But if it does, 2-4 inches would be possible and it would stick on more surfaces than today’s snow given the colder temperatures.

Here’s a snap shot of some of the model snowfall simulations:


GFS model snow simulation (WeatherBell.com)

European model snowfall simulation (WeatherBell.com)

HIgh resolution NAM model snow simulation (WeatherBell.com)
Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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