From the ABC 7 Weather team

Snow at opposite ends of the season

April 22, 2012 - 05:02 PM
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Here we are 8 days out from the end of April and possibly the largest snowstorm since last winter is honing in on the western Maryland and Pennsylvania mountains. Meanwhile, the District finally gets a nice soaking with some much needed rainfall!

A low pressure off the Carolina Coast is moving north along the coast spreading rain across the District Sunday afternoon. The rain will amount to 1.00 to 1.50 inches by Monday morning. This will help chip away at the 5.14 inches deficit that started on New Year’s Day.

The biggest story with this storm system is the incredible heavy snow that will wallop the Allegheny Mountains/Laurel Highlands to start off the work week. As the low moves north, it will draw cold air in along its backside. Rain will change to snow from Interstate 80 south across western and central Pennsylvania and then into western Maryland.

While it’s difficult for snow to accumulate this time of the year, especially during the day as the sun angle often overcomes the cold air to keep the snow liquid form as it falls on grassy/street surfaces, this storm is rather unique.

The upper-level center of the storm will likely travel right up I-81 towards Hagerstown on Monday and then scoot north across the Pennsylvania Laurel Highlands during the evening and overnight. In the core of this upper-low, very cold air will be found just above the surface at 1,000 to 2,000 feet where temperatures will be in the lower 20s. While snow will mix with the rain in the valleys, at 1,000 feet, the Blue Ridge will likely pick up an inch in grassy spots while ultimately, the heaviest snow will likely fall nearest to the upper center as it crosses the colder elevations of the Allegheny Mountains Monday.

The fast downward momentum of the heavy snowfall rates near the upper-low will bring down those colder temperatures aloft, cooling bridges, overpasses, the grass and secondary road surfaces to allow for quick accumulation. In case you want to see snow here in the District, watch closely because a few snowflakes or ice pellets will likely mix in with the rain in the afternoon and evening as the upper-low makes its closest appearance!

The upper-level center will intensify the surface low, which will rotate inland across southern New England. The counterclockwise motion of air around the surface low will bring strong northwest winds across very warm Great Lakes, creating lake-effect snow. These snow bands will make it well into the Allegheny Mountains Monday afternoon into Tuesday. So, two mechanisms are at play for a significant mountain snow event…great upper-level forcing and the lake-effect machine.

Winter Storm Warnings and Winter Weather Advisories have been posted in much of western and central Pennsylvania into far western Maryland. Amounts will range from 1-2 inches in the hills outside of Cumberland, Md., to 3-5 inches in places like Frostburg and Westernport, Md., to a foot along the highest ridges of Garrett County, including Keyser’s Ridge and Backbone Mountain. Farther north, 9 to 15 inches will fall in places like Somerset and Johnstown, Pa., with up to 18 inches along I-80 in northern Pennsylvania.

Due to the heavy, wet nature of the snow falling on trees already well in bloom will cause widespread power outages and falling of limbs and branches. Those with plans to travel towards Pittsburgh or Morgantown should keep a close eye on the weather tomorrow and Tuesday. I-68 and the Pennsylvania Turnpike could turn treacherous with snowfall rates of 1-2 inches per hour causing whiteout conditions west of Cumberland, Md. Fallen branches could crowd secondary roads in rural spots.

The snow has been on the tail ends of the winter season. Record early-season snow hit the Laurels in October. Snow accumulated 1.2 inches in Philipsburg, Pa., 1.0 inches in Ebensburg, Pa., and 0.7 inches at Laurel Summit, Pa., on October 2nd. This was the earliest in the season accumulating snow has ever been recorded in the Pennsylvania Laurel Highlands! In the middle, the weather was mild and dry with above-average temperatures and below-average snowfall and now this early week whopper will put the icing on the cake!

Stay safe if your plans take you out to the mountains and check back to WTOP and ABC7 for the latest forecasts.

 

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