Saturday, July 07, 2012

Scattering of Severe Weather Tonight & Tomorrow

Let's preface this post by saying the following -- some of you may not get any thunderstorms this weekend. However, some of you probably will...and those that do have a chance of getting strong if not severe thunderstorms.  A slight risk of severe weather is out for the Mid Atlantic for today and tomorrow...with today's risk centered over Eastern Pennsylvania, New Jersey, and Metro New York.  A cool front is sliding south into a hot, moisture-rich airmass.  The front has some "spark" to it but unlike past fronts that have provided better strong and severe storm events in our region the dynamics along the frontal boundary itself are rather modest.  Add to it a fairly robust "cap" in the atmosphere in the warm sector south of this front and you have a setup that results in scattered but not widespread thunderstorm activity.  That said, there is a pretty decent line of thunderstorm activity this morning across Lake Ontario back west into Ontario itself (to the north and west of Toronto), which is pushing east and east-southeast towards Upstate New York and eventually Southern New England.  This line could help fire off additional thunderstorm activity later on today on its western fringes...but anything that fires will be more scattered as this more robust line seems to have its sight set on New England.

We should be pretty dry through at least mid afternoon before thunderstorm chances increase in the Poconos.  Scattered thunderstorms will develop to our north, perhaps influenced by this morning's line in Canada, sliding south through the evening hours.  The greatest threat with any thunderstorms, should they develop, is gusty winds...although some hail can't be ruled out in the strongest and largest thunderstorms.

In terms of modeling, the three computer models vary a bit on placement of any thunderstorms this evening...the NAM is the closest to us with a couple of strong cells over Trenton and Bucks County after 10 PM tonight, with the GFS and Euro painting better chances towards New York City and into Connecticut, respectively.  Again, the scenario from the computer models depicts a more scattered thunderstorm breakout for the afternoon and evening.  Whether that scenario holds true or not remains to be seen...but in terms of timing, look for anything locally this evening and tonight on the heels of a hellishly hot day.

With the front sliding a bit south tonight, the threat for severe shifts south a bit for Sunday, with a slight risk out for areas generally along and south of I-195 and the PA Turnpike.  The focus area is highest south of the city (30% chance of severe in South Jersey and Delaware within 25 miles of a point).  With tomorrow's threat, scattered storms will develop along the front again in the afternoon, pushing east with a slightly more favorable setup for severe in place than today as some upper level energy interacts with the front.  This could result in a greater number of severe thunderstorms than what pops today.

That said, some spots do miss out on thunderstorms over the next two days...but the one thing that will not be missed is the demise of the heat wave...that is still on track after Sunday from Philly on south, with it perhaps ending after today from Allentown and Reading on north.

More:  Current Weather Page