From the ABC 7 Weather team

Snow in D.C. this week: What are the odds of accumulation?

December 6, 2011 - 02:51 PM
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Will Thursday be a repeat of this October's historic "Snowtober" storm? ABC7's meteorologists discuss the snow odds.

How much snow will the D.C. region get on Thursday morning, and will it stick? Pictured: Trees knocked down by wet snow after the 2011 Halloween nor'easter in Granby, Conn. (Photo by Dave Ginsberg)

Perhaps you have heard talk of snow on Thursday. Perhaps you've read that it is going to be MAJOR, a virtual repeat of the "Snowtober" nor'easter that buried parts of the East Coast this Halloween. Perhaps you've even seen the new Winter Storm Watch for Wednesday afternoon through the same evening, with 4 to 7 inches of snow possible.

Well, let the ABC7 weather team put your mind at rest. While it's true that flaky white stuff is likely to fall from the sky early Thursday morning, there are not many indications that this will be a huge problem-maker. (Or even enough to build a snowman in D.C.) That Winter Storm Watch is for areas above 1,500 feet, by the way. We're talking about towns in Maryland's Allegany County and Highland like Frostburg, Hightown and Mount Storm, which judging from their snowlarious names are used to a little powder now and then.

The ABC7 meteorologists have kindly sent their thoughts over to StormWatch 7 blog beginning in an e-mail chain that began late last night. Here they are, in chronological order. Note that the weather is constantly evolving, so keep current with the latest D.C. forecast and weather tweets.

Ryan Miller: I had my students outside [Monday] after we examined some model data hinting that some snow may work in early on Thursday. We went outside and looked at soil temps (in Arlington) and found that surface soil temps were between 44 and 47 degrees F (6-8 degrees C). At a depth of 15 cm soil temps were trending about 1-2 degrees colder than the surface. (Ed. note: That means any snow will have trouble accumulating.)

Chad Merrill: It does look eerily similar to the October snow event… 500 mb vort max coming northeast up the coast with significant dynamic cooling that could cause impressive snowfall rates for maybe an hour or so during the time frame of Midnight to 3 a.m. on Thursday morning after the changeover takes place. NAM is closest to the coast and GFS a little farther east and 21Z SREF a bit south and east, too… Looks to me like it would bring half to an inch of snow to the grassy areas and up to 2 inches in the higher elevations west of the Metro area back to the Blue Ridge (if NAM verifies). Fast system for sure… think sunshine returns by dawn on Thursday and the snow melts by midday in the Metro. But, given the hour of heavy snow that could fall overnight Wednesday, it wouldn’t surprise me if sidewalks and secondary roads get a small coating... less than ¼ inch. Major interstates would be just wet. Those are my thoughts on this event as it looks now.

Adam Caskey: I back up Chad in the sense that there could be some cooling and minor accumulations locally. Soil temps are up and road temps are currently in the 50s, but it will only take an hour or two of heavier snow to cool the surface and cause some areas of slush. We've seen it before and I wouldn't be surprised if decks, then grass, and then possibly some secondary (and north facing secondary) roads get minor slush. Possibly more west of Blue Ridge. It won't be easy to accumulate, but I don't think it should be ruled out just yet.

That said, the 06z NAM and GFS pull slightly warmer 850 air into central Virginia. According to these profiles, a changeover is still expected with snow possible from about 03-06z locally. We'll have to see how future runs handle it.

...And the HPC has a probability of only "at least 40%" for greater than or equal to 4" which only encompasses the mountains... west of I-81.

Chris Naille: I agree with Chad and Adam at this point. 06Z NAM is going crazy with potential snowfall totals indicating 6.6” of snow in HGR and is still just a bit behind Euro and GFS with timing. As Ryan and everyone else has pointed out the ground and road temps will be too warm for accumulations other than perhaps a little slush west of the BR and in higher elevations on roads and sidewalks. Accumulations on grassy areas look to a coating at best around the Metro with perhaps up to 2 inches of wet heavy snow mainly west of the BR and at higher elevations. This looks like something to talk about but I don’t think at this point there will be much impact at all to the morning rush. Most if not all snow will melt quickly after sunrise Thursday. As Adam said we will monitor future runs to see what if anything changes drastically.

Alex Liggitt, in his latest forecast: The main energy from a trough currently moving through the Plains states will push into our region Wednesday night into Thursday morning. As this happens, an area of low pressure is expected to develop off the Eastern Shore and move northeast into the Atlantic. It appears enough cold air will get wrapped into this low that precipitation behind the low will change into snow before coming to an end Thursday around sunrise. There is the potential for some measurable snowfall, though it looks like it will be light and mainly only accumulating on grassy areas. Areas such as Loudoun and Frederick Counties and points west will have the greatest chance for measurable snowfall, but there is still the chance for a few slick spots in Montgomery, Fairfax and even the District itself. The time period for snow appears to be around midnight to 4 a.m. Thursday morning. The sun may be breaking out across the region for the morning commute.

Bob Ryan: Rain tomorrow may end briefly as wet snow in the D.C. area from midnight to 3 a.m. Thursday. I don’t see any big commute problems during Thursday morning.

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