Friday, February 5, 2010

Great Snowy Expectations (Part 2): Awaiting the D.C. Blizzard of Feb. 2010

So this is the 6UTC (1AM EST) Feb. 5, 2010 NAM output showing 42 hour cumulative precipitation valid at 60 hour.

These QPF (quantitative precipitation amounts) over our area are ridiculously high -- are to believe. Even at a 10 to 1 ratio, this 3" QPF for D.C. would mean 30 inches of snow. That is not going to happen. Not at National Airport it isn't --that would be a once in a 500 year event, I would estimate. These QPF amounts seldom come to pass in snowstorms.

If I had to guess, I would say DCA will end up with about 13 to 14 inches, BWI with 19 to 21 inches, and IAD with 18 to 20 inches of snow on (hard to measure) liquid equivalents of about 1.5 inches (less at DCA because of how they measure it).

Now that's just a guess based on how these things usually play out. What is very unusual is to have two of these big snowstorms in one winter -- I have not seen that before in the D.C. area. They are usually separated by 7 years or so.

Anyway, everything gets underway a little later today. I never saw a situation where South Jersey (including Cape May County) is under a blizzard warning while Sussex County, N.J., had no advisories. At least that was the situation a few hours ago, but the precipitation cut-off is expected to be very sharp.

Here is a map of the National Weather Service's Mount Holly, N.J. (PHI) County Warning Area (CFA). As I can't figure out how to do a screen capture on my new computer, I can't get the legend on the side but the lavender - pink is winter storm warning and the crimson orange - red is blizzard warning. The darker blue is winter storm watch. The beige for Sussex County is just a "short term forecast" (no warnings).

Here is the Sterling, Va. (LWX) CFA for the Baltimore - Washington area. The entire LWX area is in winter storm warning condition, as is a good portion of the Wakefield, Va., (AKQ) for the Virginia Tidewater area.

Anyway, it's all just a matter of waiting now.

I never did go grocery shopping.

--Regulus

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