Potential For Severe Weather Saturday
The Storm Prediction Center has put our region under a slight risk for severe thunderstorms on Saturday as a cold front will be moving east for the upcoming weekend. This low pressure system is organizing across the Plains, where a moderate risk of severe weather is expected today in Nebraska and Iowa.This storm system will move east and northeast through the Great Lakes on Friday will fire off additional severe weather across Illinois and Indiana. Friday's severe weather outbreak, although in a somewhat weakened state, may also impact our region. The first may be in the form of what is called a MCS (or mesoscale convective system) which will ride east along a warm front that will set up along I-80 in Ohio and then spread east through Ohio late Friday night and then across Pennsylvania early Saturday. This MCS, if it develops as the the GFS and NAM models say it will, should impact our region in the mid morning hours on Saturday. This MCS may be in its weakening stages so the odds for severe from the first batch of storms may be on the low side.
The potential for severe weather on Saturday is dependent on a couple of factors. One is the MCS and its timing. If the storm complex moves through here (or just north) early enough in the day and Philadelphia gets into clearing during the peak heating times of the day we should see an increased risk of strong to severe thunderstorm development in the afternoon as instability parameters are strong (see below and look at all the pretty colors over our region -- there's a lot of shear present in the atmosphere plus the traditional instability factors not shown on that map are sufficient for severe).
However, if said MCS scoots through the region during the later morning hours and is slow in departing the region, it will limit the amount of potential instability in our region as cloud cover will be present during the peak heating times of the day. Scattered severe thunderstorms are possible in the afternoon but the odds of more widespread strong to severe thunderstorm activity would diminish (still possible, but not as likely). Any of the afternoon thunderstorm development regardless of whether it's more widespread or scattered in nature has the potential for gusty winds and possibly a tornado or two due to the presence of wind shear (wind changing direction with height) in the atmosphere.May 31st has some history behind it around the Mid-Atlantic. It's the tenth anniversary of the F-3 Lyons tornado that struck the small Berks County community. The storm system that caused the Lyons tornado also caused a widespread derecho event across the Great Lakes. May 31st, 1985 also brought a widespread tornado outbreak to Pennsylvania, with 22 tornado touchdowns in Western and Central PA, including four F-4 tornado touchdowns and one F-5 that struck both Ohio and Pennsylvania. I'm not comparing this Saturday to either storm complex but the potential exists for May 31st, 2008 to have some nasty weather around these parts.
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