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Posted at 10:58 PM ET, 02/19/2008

Update: No Changes to Light Snow Forecast

By Jason Samenow

We're still thinking light snow is likely tomorrow -- particularly between about 10am and 6pm in the metro area. Accumulations should generally be between a dusting and 1". Areas to the south of the beltway may get a little less, and areas to the north may get a little more. The snow may not accumulate much at all downtown due to somewhat warmer urban surface temperatures.

Temperatures will likely be at or below freezing when it snows so a few slick spots could develop on less traveled, untreated roads - particularly during any moderate bursts of snow, which may also briefly reduce visibility. Be particularly careful on bridges, ramps and overpasses.

No SchoolCast as I think the snow will start too late to impact schools.

By Jason Samenow  | February 19, 2008; 10:58 PM ET
Categories:  Updates  
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the GFS is not looking too good for the DC area for the storm later this week. It is looking great for Trenton and above, but DC it looks to warm for a lot of snow.

Posted by: thejesse2442 | February 19, 2008 11:17 PM | Report abuse
No SchoolCast as I think the snow will start too late to impact schools and result in early closings.

does tht mean tht the snow will start too late to result in early closings OR that the snow will result in early closings?

Posted by: strangldangel | February 19, 2008 11:23 PM | Report abuse

I'm thinking no early closings.

Posted by: Jason, Capital Weather Gang | February 19, 2008 11:27 PM | Report abuse

Snow will start too late TO result in early closings. By the time it started to make an impact, it would already be around the time schools are letting out anyway.

Posted by: Jamie Jones, Capital Weather Gang | February 19, 2008 11:28 PM | Report abuse

Cold out there tonight... just got home. Seems like we'll have a solid amount of time where the temps are cold before the Thursday night event begins... hoping that will cool surface temps enough around the area to increase the chance of whatever falls sticking. This should be an interesting few days!

Posted by: Skywalker in Silver Spring | February 19, 2008 11:31 PM | Report abuse

Seeing some of the 0Z model data, it appears to me that liquid to snow ratios towards the latter part of the day Wednesday may reach 15:1 or 18:1 as 850mb temperatures aloft cool dramatically. In my own personal view, I think this clipper is more likely to over-perform than to under-preform. I am still in agreement with Jason's forecast, however. And I think snow will have a tough time sticking on paved surfaces due to sun angle and yesterday's high temperatures near 50.

Also, thejesse2442, I think that the late week storm will trend colder just as this clipper has. I believe the models are underestimating the extent of Arctic cold to the north.

Posted by: Josh, Capital Weather Gang | February 19, 2008 11:39 PM | Report abuse

Josh-- Agree with you on ratios and considered that. But the effect of the high ratios on accumulations may be compromised a bit by middle of the day timing. Unless it snows hard or is REALLY cold, it's difficult to get stickage in late Feb during the middle of the day. The GFS did trend a bit wetter in the latest run, so don't disagree it could overperform a little.

Posted by: Jason, Capital Weather Gang | February 19, 2008 11:49 PM | Report abuse

" appears to me that liquid to snow ratios towards the latter part of the day Wednesday may reach 15:1 or 18:1 as 850mb temperatures aloft cool dramatically..."

850 mb is not the cloud region that determines SN:H2O ratios. The temperature analysis is made at near the cloud top.

Posted by: TQ | February 19, 2008 11:53 PM | Report abuse

Tommorrows system looks a little better with a little more of a Southern track, wouldn't b surpised if a few areas got an 1" or a tad more. Unfortunetly late week still looks like a snow/sleet/rain storm, of course, areas N & W should see more frozen prec. Still no major pattern changes thru at least early March, La Nina still influencing the weather.

Posted by: VaTechBob. | February 19, 2008 11:55 PM | Report abuse

TQ: Agree that cloud temp/physics play the key role in snow/liquid ratios, but temperatures through the column (and thicknesses) are important factors and can be helpful proxies for these ratios. See this link.

Posted by: Jason, Capital Weather Gang | February 20, 2008 12:24 AM | Report abuse

I/ll take your point that colder temperatures in the boundary layer are better for crystal growth and maintaining higher SN:H2O ratios associated with 'clipper' systems than warmer temperatures.

Posted by: TQ | February 20, 2008 10:04 AM | Report abuse

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