Two rounds of snow flakes possible Tuesday, but shouldn’t amount to much

December 16, 2013

Two weak disturbances in the atmosphere’s flow, known as clippers, could put down some snowflakes in the Washington, D.C. area at times Tuesday, but little (or no) accumulation is expected.

Key points

* The first clipper zips through the region late tonight into early Tuesday morning when temperatures should be cold enough for snow.

* The second clipper whizzes by  late Tuesday afternoon and evening.  By that point, temperatures may be warm enough for just rain, especially from the District and to the south and east.

* The colder northern and western suburbs (Montgomery, Howard, and Loudoun counties) have about a 40-50 percent chance of at least a dusting, mostly from the first clipper. The second clipper probably puts down mostly “conversational” snow that does not stick.

* Places inside the Beltway could get a dusting from the first clipper (20-30 percent chance). Accumulating snow is unlikely from the second clipper, which may be more rain.

* The southern half of the region has low chances of accumulating snow from the first clipper (10-20 percent chance) and may see no snow at all from either clipper.

* I generally like this table (below) from the National Weather Service, which rounds up snowfall chances through Tuesday night:


Chances for different amounts of snow in the D.C. region through 7 p.m. Tuesday night (National Weather Service)

* In a boom scenario, a little more than an inch of snow falls somewhere in the metro region (with the colder northern and western areas favored, and from the first clipper); in a bust scenario, the entire region sees nothing more than scattered flurries and/or rain drops.

* Caution: with small weather systems like this, there can be “surprises” where heavier than expected snow occurs somewhere due to the development of a localized heavy band, which are impossible to predict ahead of time.

Details: Clipper 1 (early Tuesday morning)

Of the two clippers, the first has the most potential to produce a bit of snow late tonight into early Tuesday morning, but its upside is limited.

Clippers, when they enter the region from the west (most of the time), typically have a lot of their moisture wrung out by the mountains.  Any snow that makes it over the mountains is often patchy and light. This clipper – like most – is likely to be moisture-starved.

Another factor working against it is its track.  The most snow from clippers usually falls just north of its track – and this one may pass directly over us, which would place northern Maryland and Pennsylvania in the best spot for snow.


NAM model simulates the vorticity or spin center at around 18,000 feet (500 mb) at 7 a.m. Tuesday morning shaded in orange entering northern Virginia. This is so-called clipper one. (StormVistaWxModels.com)

While this clipper isn’t taking an ideal track and its moisture supply is meager, temperatures may just be cold enough for snow to stick a bit, particularly in the colder northern and western suburbs.

The European model (shown below) simulates a dusting to an inch in the northern suburbs from this first clipper.


European model snow simulation through 1 p.m. Tuesday (WeatherBell.com)

Bottom line: Between around 1 a.m. and 9 a.m. Tuesday morning, scattered snow showers and flurries are possible in the region.  Chances are around 40 percent in the District and south and east (where a dusting is possible, not likely), and closer to 60 percent in Loudoun, Frederick and Howard counties which could get a dusting to an inch.  Temperatures should be around freezing in the District and slightly below freezing in the colder suburbs (28-31) which would allow for some sticking.  At worst, this clipper could produce a few slick spots and briefly reduce visibility in the pre-dawn to early morning hours.

Details: Clipper 2 (Tuesday afternoon-evening)

After a brief break late Tuesday morning into Tuesday afternoon, this second clipper races into the area.  It may be a tad stronger and take a slightly better track (a bit farther south than the first) to produce some light precipitation in the region (compared to the first), but temperatures may well warm too much for any accumulation.  From the District and to the south and east, where it may get to 40 or higher Tuesday afternoon, precipitation may fall as rain or a rain/snow mix.


NAM model simulates the vorticity or spin center at around 18,000 feet (500mb) at 7 p.m. Tuesday morning shaded in orange and red entering central and  northern Virginia. This is so-called clipper two. (StormVistaWxModels.com)

If precipitation continues to fall into Tuesday evening when temperatures are falling, a dusting or so is possible, mainly in colder north and west suburbs.

Bottom line:  Between around 3 p.m. and 11 p.m. Tuesday afternoon and evening, snow and/or rain showers are possible – with somewhat better odds of precipitation in the northern suburbs (60 percent north versus 50 percent south). Little or no snow accumulation is likely, except in the colder suburbs where a dusting or so could fall.

 

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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Jason Samenow · December 16, 2013