Sunday, January 9, 2011

Weather Update - 4:45 PM Sunday

Winter storms are rarely "well-behaved" here in the Mid-Atlantic and this storm is no exception. However, as this storm approaches the area, the picture continues to become more and more clear. With that said, this is not 100% etched in stone yet.

Here is my forecast for snow totals from Monday night into Tuesday night.

***Update 10:20 PM***
I just looked at the latest data and have slightly adjusted this graphic so that it can be more specific. I think some areas west of I-95 have the potential to pick up a little more than the 1 to 3" I previously posted.

Yesterday I showed you a forecast sounding from the GFS computer model. It's a forecast of temperatures from the surface (bottom of image) all the way up to 50,000 feet in the upper atmosphere (top of image). I highlighted the freezing line in red. The right pink line is the temperature forecast. When it is to the left of the red line, temperatures are below freezing. When it is to the right, it is above freezing. Notice a large area of above-freezing temps at around 5,000 feet, indicated by the red arrow. This is your typical sleet scenario (ice pellets).

I think it's safe to say that we will see a mixture of sleet and snow in Richmond and areas to the south and southeast. In fact, far southeastern VA will be seeing mainly rain. This will eat away at our snow accumulation potential. There is also the threat for some freezing rain in south central and southeastern VA, but this band will be very narrow.

This is a difficult forecast because the powerful storm system currently moving across the Deep South is going to weaken when it moves into our skies. Once the surface low develops off the coast, it will receive reinforcing "lift" from a large upper level wave moving in from the northwest. From 7 PM Tuesday to 1 AM Wednesday (00Z to 06Z), this low will explode. You can see this on the ECMWF ensemble forecast below.

During this time, heavy bands of snow will redevelop, however, it might be too late to affect Central VA. That is why I'm going for higher amounts in Northern VA. I've posted all of the computer forecasts for snow accumulations. Notice how the NAM, ECMWF and RPM all reflect this trend (though NAM and RPM are very aggressive with snow totals in eastern North Carolina).

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