Three chances for light snow through Monday; bigger storm midweek?

The D.C. area has three opportunities for snow between Saturday and Monday, but all of them have limited moisture and none look terribly consequential.  A fourth system could produce more meaningful precipitation midweek, but confidence in its specifics is low.

1. Saturday system overview: 50 percent chance of snow

Timing: Late morning into the afternoon.

Temperatures: Low-to-mid 30s

Snow intensity and amounts: Light snow. 40 percent chance of a dusting to an inch, mainly on grassy areas


GFS model simulates less than 1″ of snow over the D.C. metro region Saturday. It is the most aggressive model for snow. (WeatherBell.com)

Concerns: Minor. We’re on the edge of this weather system, tracking from the Georgia coast northeast out to sea off the North Carolina coast.  The NAM and European model simulate hardly any snow.  If snow falls, temperatures near or slightly above freezing mean minimal accumulation prospects.

2. Sunday system chance overview: 40 percent chance of snow

Timing: Late afternoon into the evening

Temperatures: 35-40 falling into the 20s

Snow intensity and amounts: Light. 20-30 percent chance of a dusting to 1″ (highest chances north and northwest of D.C.)


GFS model shows some light precipitation (rain and snow) having accumulated Sunday afternoon. The purple line shows temperatures are above freezing except in D.C. far north and west suburbs through 7 p.m. (StormVistaWxModels.com)

Concerns: Minor. This disturbance passes to our north.  If it spreads precipitation into the region Sunday afternoon, it may be begin as rain  – limiting accumulation prospects – before changing to snow in the evening.

3. Monday system overview: 40 percent chance of snow

Timing: Highly uncertain.  European model initiates snow pre-dawn, NAM model suggests not until Monday night.  GFS keeps system to our south.

Temperatures: 20s into 30s.

Snow intensity and amounts: To be determined…most likely light.


European model shows some light snow having fallen over the metro region through 7 a.m. Monday morning. Temperatures are below freezing as indicated by location of purple line. (StormVistaWxModels.com)

Concerns: Minor.  This disturbance won’t have a lot of moisture to work with but the NAM and European models suggest it will have a little more than the weekend systems.  Stay tuned on this one.

4. Midweek system overview: 40 percent chance of snow

Timing: Highly uncertain (see technical discussion below), but best chance Wednesday into Thursday.

Temperatures: 20s and 30s.

Snow intensity and amounts: To be determined. Some potential to be moderate.


European model shows a significant area of low pressure off the Mid-Atlantic coast 1 a.m. Thursday morning. The rain/snow line is just east of the District. (StormVistaWxModels.com)

Concerns: Moderate.  The European model shows a storm coming out of the Gulf of Mexico up the East Coast with plentiful moisture.  The GFS model, however,  keeps the storm weaker and suggests rain is more likely than snow.  Taken literally, the latest European model would be a significant snowstorm for the D.C. area, but we’re very close to the rain/snow line.  Slight changes in its forecast could mean more of a wintry mix or rain threat.  As Wes Junker will discuss below, this is a not a very predictable pattern.

 Technical discussion on these snow opportunities and the pattern, by Wes Junker

cwg_Junker

Saturday through Monday offers several chances of light snow.   None of these weak systems is likely to produce more than a period of light snow though the European model did entertain the possibility of someone getting an inch or two pre-dawn Monday morning into Monday afternooon.

Very fast flow with a numerous weak upper level impulses makes timing the shots of precipitation challenging even in the shorter time ranges.  Such flow has always been a forecaster’s nightmare as timing any impulse and whether it might work in concert with another one becomes a pure guessing game.  Therefore, speculating about the specifics of a  potential low tracking along the East Coast in the middle of next week is pretty foolish.  Yes, there is some potential for a storm but it’s way too early to entertain thoughts about when it might occur and what type of precipitation it might bring.

In the short range,  this morning’s GFS model liked Saturday morning for a dusting and then a period of light rain or snow Sunday afternoon but kept any precipitation Monday well to our south. Today’s NAM model kept Saturday’s system just to our south but and then clips us with light precipitation Sunday evening and hints at more snow possibly developing Monday night.   The bottom line:  most of us could see periods of light snow from Sunday through Monday.  One of these periods still could produce accumulating snow, probably on the order or a dusting to a couple inches at the most.  However, we also could end up with just conversational snow with no meaningful accumulation.

Why won’t you be more definitive about the various storms?

The plume diagram below does a great job of illustrating how difficult is will be to try to predict times when snow or rain might occur during the next week.  Each line represents a model run having identical physics but minor differences in the initial conditions.  When a line is climbing precipitation is falling, the steeper the climb, the heavier the precipitation.  Times when the line is flat and parallel to the base line, that individual simulation or member is predicting no precipitation.   During periods when the pattern is predictable, the lines tend to cluster together, when the predictability is low like now, they tend to be spread out.


The diagram above is suggesting only light precipitation will fall on Saturday and whatever falls would likely be snow.  However, by Sunday, the ensemble members suggest that precipitation from any system might fall as either rain or snow with the snow chances increasing towards Sunday night into Monday morning.  The spread of the different model solution by Tuesday evening is huge with some models developing snow by Tuesday night while others hold off until Thursday night.  In general, the later the mid-week storm holds off ,the higher the likelihood of rain falling rather than snow.  The extra time allows the cold high over the northeast to track into the Atlantic minimizing the chances of having cold air damming take place for an extended period.

The ensemble spread (above) mirrors the differences in the operational model runs from last night and this morning.   The operational European model spreads snow into the area Monday morning and again Wednesday night but then would change the snow to rain by Thursday morning.  This morning’s GFS would also argue for the high slipping off the coast before precipitation arrives from the mid-week storm, suggesting the bulk of the precipitation would fall as rain. My guess is there probably will be a storm sometime towards the middle of next week. The later the storm arrives during the week the more likely rain or a wintry mix changing to rain becomes compared to snow.

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Jason Samenow · February 7, 2014

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