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Posted at 02:13 PM ET, 09/29/2011

Snowflakes possible in nearby mountains Saturday

Cold front passes through mid-Atlantic region Friday (NOAA)
A major fall cold front passing through the region Friday will send temperatures tumbling Friday night. And as a cold pool of air aloft flows across the elevated terrain to our west, yes, some snowflakes may fly between late Friday night and Sunday morning.

The National Weather Service writes in its forecast discussion:

cannot rule out a few wet snowflakes Friday night/early Saturday along Allegheny Front

The high spots favored to see some flakes along the Allegheny Front include Dans Mountain west of Cumberland, Md. and around Mt. Storm, Dolly Sods and Mount Porte Crayon in WV.

Precipitation between 5 am and 11 am Saturday colored in green. To the left of the blue line running north-south - which represents freezing at around 5,000 feet, temperatures at high altitudes will be cold enough to support some wet snowflakes. (
If you go even farther west, there may even be enough snow to whiten the ground around the peaks of ski areas such as Wisp, Canaan Valley, and especially Snowshoe. In these areas, moisture will be enhanced by flow off the Great Lakes.

Temperatures at all of these locations will struggle to reach 40 degrees Saturday.

Snow in D.C. and nearby suburbs?

Not going to happen. By the time the atmosphere cools sufficiently for precipitation to have a chance to fall as snow (Saturday night), the air will have dried out. I can’t totally rule out some wet flakes mixing in with rain showers in some of the high spots in Loudoun or Frederick county at some point Saturday, but it’s highly unlikely.

Nevertheless, Saturday brings windy, chilly conditions to the entire region. Temperatures may struggle to exceed D.C.’s record low maximum for the date of 56 degrees set in 1899. And if we get some sunshine and mix that with the very cold air aloft, some thundershowers with small hail could develop Saturday afternoon. So a very unsettled, blustery day is on tap.

Big jet stream dip Saturday with upper level low centered over northwest Va. will create instability and cold air aloft (
This wintry scenario is being set up by a digging jet stream plunging from the Upper Midwest today all the way south of the mid-Atlantic by Saturday, as shown in the image to the right.

The cold front coincides with the leading (downstream, eastward) side of the jet stream (offshore by Saturday in the image to the right). And at the base of the jet stream, a bowling ball-like upper level low pressure system(colored in orange and red over NW Va.) rolls by with cold air at high altitudes and rising air (supporting precipitation).

For warm weather fans, the good news is that this crashing jet stream will quickly retreat Sunday into Monday, allowing sunshine and warmer weather to gradually filter back in.

By  |  02:13 PM ET, 09/29/2011

Categories:  Latest, Winter Storms

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