Mid-Atlantic Discussion – Mar 23, 2011 and this weekend


A rather unusual severe weather setup as a low pressure system rides along a frontal boundary that is NW-SE oriented from central OH into central MD. Warm-sector instability on the order of 500-1000+ J/kg SBCAPE will develop over WV and western VA during the afternoon, which will help initiate a few areas of showers and storms. A convergence area over the Appalachians will help trigger storms early, with better instability upstream ahead of the southward-moving cold front that will move through OH and WV during the late afternoon and early evening. Things will look a little messy on radar at first, but eventually some strong/severe cells will form in the westernmost parts of the region. The main threat from these storms will be hail and wind damage, with an isolated threat for a few tornadoes. Speed shear is good with this system, but winds will be largely unidirectional, which will hinder tornadic development. Upper-levels are somewhat favorable as left-exit region divergence and some support from the 500mb vort. provide good synoptic lift.

As these storms push east into the Apps. and coastal plain, they will likely lose some intensity as the surface instability wanes. However, elevated instability should be sufficient to maintain thunderstorms with hail (maybe severe) and gusty winds (likely not severe) as the storms reach the DC/BWI region in the early evening. Depending on the amount of the elevated CAPE, storms could maintain themselves rather well and provide the area with a good lightning show.

Chase-wise, I’m considering taking I-68 to Morgantown, WV and then waiting to see where storms initiate. Should storms end up more favorable to the south, it will be a quick drive on I-79 towards Charleston, WV to get into better position.


It appears as though the cold air is a lock for Friday and Saturday. A storm system passing by to our south on Saturday is expected to bring some cold rain and possibly snow into the region (…so much for that Southeast ridge). Should the colder temperatures and precipitation verify, a swath of 1-3″ or more of snow is possible in the northern half of the region. Timing the precipitation with the colder temperatures will be key in getting widespread snowfall to occur, so this system will be revisited later this week and could include a snowfall forecast map.

I will forgo this week’s What to Watch Fore(cast) as 1) I am already behind and 2) there’s plenty to track regionally this week.

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