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

dcstorms-com_prelim_snowfall_map_feb0917

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.

 

 

4 thoughts on “Preliminary Snowfall Accumulation Map Posted for Wednesday Night & Thursday Morning Storm

  1. GT

    “Is this a cruel evil joke?” my friend commented when I suggested a possibility of snow. With current temps in the 60’s and possibly the 70’s, a LOT of snow would have to fall before there’s any chance of a closure much less a delay.

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    • Tim

      Most accumulations will be on grassy surfaces, so I’m not expecting any delays in the immediate Metro Area, you would have to go well north and west where temperatures will fall into the lower 30s to have issues on untreated roadways. But there will be a period of heavy snow (Likely 1″/ hour rates for several hours). If we had had cold weather prior to this… we’d be talking about delays. This will be more of a wet, winter-wonderland snowfall.

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  2. Brendan

    Despite the very warm road temperatures, the weather service will probably still pull the plug and issue advisories due to the amounts of snow and temps being close to freezing as well as how heavy it could be. If snow were to stick it would be a very wet snow that would be difficult to manage. I think these accumulations are overdone, not trying to sound rude but it’s just too warm right now.

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    • Tim

      Brendan, the accumulations will certainly be over done if the GFS and NAM models are correct in the track remaining very close to our area. If the European model and Canadian are correct, northern Maryland could be clocked due to how rapidly these models cool the column while the snowfall rates are coming down heavy. Also if you look at my map, one could assume the following: Downtown DC – probably only 1″ on grassy surfaces (bust: dusting, boom 3″); Leesburg VA & Frederick Maryland – 3″ seems reasonable if model suite mentioned above are correct (boom 5″ in both locations). Maryland/Pennsylvania border: 4″ seems highly likely to me with a boom of 6″ (fairly confident here). Places like Fredericksburg, Quantico, Culpepper, Stafford, southern Maryland – I’m forecasting mainly a rain event, ending with some light snow. I think afternoon snow showers and snow squalls are likely as the upper-level trough swings overhead. Temperatures will be dropping as CAA (Cold air advection) rushes in and heights fall. Any of these squalls could drop a half-inch to inch of snow in the matter of 30 minutes. Again a swing further north in track in the Euro/GEM/UKmet etc… would definitely crush hopes of accumulations anywhere away from the MD/PA line. I don’t think you’re being rude at all, appreciate your opinion/feedback. Fingers Crossed!

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