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Posted at 01:00 PM ET, 03/25/2011

Some snow accumulation likely Sunday morning

Since late February, the Snow Lover’s Crystal Ball has been buried deep in the closet. But this early spring cold snap and an energetic jet stream has forced me to fish it out, as the potential for an inch or so of snow is back on the table.

Next chance of accumulating snow: Sunday, March 27

Probability of accumulating snow (1” or more): Slightly above 50%

Timing Sunday: Approximately 2 a.m. to noon

Given an unusual and impressive amount of cold air in place at this time of year (due to a big, cold area of high pressure to the northwest), we have fairly high confidence at this point that we’ll see snow pre-dawn Sunday into Sunday morning and possibly early afternoon as a disturbance zips by to our south. The big forecast questions are: 1) How much snow will fall? and 2) Will the snow stick?

Based on current guidance, here is how we see the event unfolding:

Snow is likely to begin between 2 and 5 a.m. Sunday morning. Temperatures will probably be near or slightly above freezing when the snow starts, but fall below freezing once the snow gets going. This should allow some snow to accumulate, especially on grassy areas and in colder locations west of town. Some accumulation on the roads is even possible, as model guidance suggests temperatures will drop back into mid-to-upper 20s.

However, as the sun comes up Sunday, the window for accumulating snow will gradually close unless snow falls moderately to heavily. So we think that if we’re going to get accumulating snow, it’s probably going to have to fall prior to 9 to 11 a.m. when temperatures will slowly rise to near freezing and the late March sun facilitates melting. After 11 a.m., as the snow is winding down, it might even mix with or briefly change to rain/drizzle. Still, Sunday afternoon will be very chilly - with highs only in the mid-30s - more than 20 degrees below average!

Model output varies giving us between about 0.1 and 0.3” liquid equivalent precipitation which in the middle of winter would suggest around 1” to 4” of snow (depending on the circumstances). But it’s not the middle of winter so we must take that into account.

Given we’re just north of the heaviest precipitation with this system and in light of the time of year/sun angle issue, we think generally around 1” of snow is most likely in the metro region with amounts increasing to the southwest and decreasing to the east and northeast. For snow lovers, we could see a best case scenario of 2-3” (with isolated 4” totals) if the wettest models (e.g. the GFS and SREF) are correct AND we get steady snow from 3 to 9 a.m. when temperatures are near or below freezing. On the other hand, if the drier models are correct (e.g. the NAM and last night’s Euro), a wet dusting to an inch is about all we would see. The drier models show a sharp northern cutoff which we need to watch closely. That cutoff would be the most likely candidate to lead to a forecast bust (on the low end).

Summary points:

* Our best bet right now: Around 1” of snow D.C. metro - mainly on grassy areas downtown, near Potomac, and urbanized parts of suburbs

* Probabilities: Less than 1”: 45%, 1-2”: 30%, 2-4”: 20%; 4”+: 5%

* Highest snowfall amounts southwest of D.C., especially in elevated areas (high elevations of west central Virginia may see 4-8” of snow)

* Sticking most likely on grass, but some accumulation on roads possible through 8-9 a.m. Sunday morning, especially west/southwest of District where it’s colder and probably snowing harder.

Tomorrow we will post a snowfall accumulation map (assuming we’re still predicting accumulating snow) and post thoughts from Wes Junker, our winter weather expert.

By  |  01:00 PM ET, 03/25/2011

Categories:  Snow Lover's Crystal Ball, Latest

 
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