Harrisburg-Lancaster, PA Supercells
By Stephen Barabas on August 15, 2012, 2:24pm
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Tuesday August 15th was a marginal day for severe weather. But, since we're coming down to the wire for chances of severe storms in this part of the country, Quincy Vagell and myself decided to head on into Pennsylvania to try and intercept. During the morning there was a lot of clouds and some rain associated with the first weak area of vorticity which did deliver some severe weather to Penn and New Jersey through the over night and early morning. So, we weren't entirely sure how the instability would be for the day.
Leaving around noon, we headed for Scranton and then decided the obviously choice was to drop as far south as we felt was necessary. As we headed west, the clouds began to break up and temperatures gradually rose to the lower 80s. By 5pm or so we were in Harrisburg, PA, waiting for storms to initiate. Storms had fired off to our west but weren't looking all that impressive. It wasn't until around 7pm that storms really started to get going as the second and stronger vort-max pushed into the area.
Around this time a pretty impressive and initially nearly stationary supercell fired up along I-76 just east of Harrisburg, so we went for it. As we got to it the storm split, one heading southeast and the other part moving north. Both had pretty well defined rotation of cyclonic on the south mover and anti-cyclonic on the north. So naturally we decided to drop to the southern storm to see what would happen. Unfortunately I-76 has large gaps for exits . . . which really threw a wrench in our maneuvering. When we finally did get an exit to drop south, the storm began to die while the northern one quickly intensified but really only lasted around an hour or so.
It wasn't until after dark that the vorticity max really got things going, with back building thunderstorms that prompted flash flood warnings. There were even several tornado warnings around Baltimore Maryland . . . and even more interesting, one nice book-end vortex developed in New York and prompted a tornado warning! SPC (Storm Prediction Center) did not issue a mesoscale discussion until around 9:30PM which was a little strange, I thought, especially with a lot of these warnings happening, including the tornado warnings.
In any case, Quincy and myself didn't see too much of anything besides explosive supercell updraft structure, and the long haul of driving a round trip of over 700 miles! That's basically like driving from the border of Connecticut/New York to the border of coastal North Carolina/South Carolina.