18z Canadian (RGEM) Model Shows One Hell of a Nor’easter

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If you average all the models and take into account the record spring-like temperatures of late we wind up with rain going over to a period of heavy wet snow with accumulations mainly being confined to grassy surfaces.  If the European and Canadian models are accurate with colder air rushing in faster and this storm deepening (or slowing down at all)… we have a very interesting forecast on our hands pre-dawn Thursday for portions of our region.  Folks from the northern Shenandoah Valley to Baltimore northeastward to Philadelphia, the Jersey Shore and Cape Cod are currently looking at their first major winter storm of the season. Yes some of the snow will definitely melt as it falls due to the warm conditions but the probability may begin increasing of 4″ or more in these locations and will need to be closely monitored.  

This leaves the Washington Area in the usual conundrum of details that still need to be worked out. You know the saying, “The Devil is always in the Details”.  I remember a February storm that rolled through the DC Area dropping over a half-foot of snow after high temperatures were in the mid to upper 60s.  There are dynamics in the atmosphere that can produce incredible snowfall rates that overcome antecedent warm conditions wreaking havoc on unsuspecting commuters.  Right now, the area that will be most susceptible to potential slush/snow-covered roadways are those of you across northwestern Virginia into the Baltimore Metro Area.

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Preliminary Snowfall Accumulation Map Posted for Wednesday Night & Thursday Morning Storm

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The image above is my preliminary snowfall accumulation map for the strong wave of low pressure that is forecast to pass pretty quickly to the south of DC on Wednesday night.  I based my map on a blend of the European, Canadian and UKmet (United Kingdom) models as I believe the GFS and NAM are currently the outliers in taking this system too far north. There is still time for the Euro, Canadian (GEM), and UKmet to move more in line with the American models (GFS, NAM) and this of course will be resolved tonight and tomorrow.

  • This storm system will mean business as there is a major temperature gradient (baroclinic zone) set up from north to south across our region.  This will allow for a period of moderate to at times heavy wet snow (strong deformation zone and frontogenetic forcing) late Wednesday night into the pre-dawn hours on Thursday. 

 

  • The exact track will be key as any shift in track further south would bring in colder air into our area pulling significant snowfall accumulations further south. Likewise, as any shift northward in track would keep the DC Area on the mild side of the system with rain being the predominant precipitation type.  Right now, the European, Canadian and UKmet are showing a track across central Virginia.  An old rule of thumb is you want to be 50 miles north of the track of an area of low pressure to have snow falling. 

 

  • The recent warm temperatures are going to crush snowfall accumulation potential (otherwise I would have gone even higher with totals across Northern Virginia and central Maryland), however, with that said, the Euro and Canadian are trying to deepen this system fairly quickly and temperatures may be at or below freezing by the Thursday morning rush hour across our northern and western suburbs with slush-covered untreated roadways. Any slow-down in forward speed of this system will greatly enhance snowfall accumulation potential across portions of our region. 

 

I won’t be surprised to see northern Maryland counties placed under a Winter Storm Watch on Wednesday morning.  These are the areas where at least 4 to 5″ or possibly more could fall due to their higher elevation and the faster change-over to snow on Wednesday night. 

 

I will provide updates as necessary as new information comes in.