May 31st Update: Tomorrow's Severe Storm Potential

Focus Area: Pennsylvania

Synoptic features:
500 mb: Negatively tilted trough
250 mb: Diffluent pattern over SErn PA from splitting branches of the jet stream.
Surface system: occluding mid-latitude cyclone

Mesoscale parameters:
Instability: LOW – SOME PRESENT
Shear: MODERATE – NOT OVERWHELMING

Conclusions:

A squall line associated with the cold front is still the best chance of seeing severe weather across the southern two-thirds of PA. Winds to 70 mph and hail to an inch thick possible. Ahead of the squall line, multi-cell clusters with some isolated super-cell activity are possible due to abundant shear and some instability, but cloud cover lowers probabilities substantially over PA. More breaks in the cloud cover between 10 am and 3 pm are necessary for this scenario to play-out, but there’s a chance of two-inch thick hail and a few isolated yet weak tornadoes if storms form ahead of the squall line.

Other notes:

Thunderstorms will be slow-movers (15-25 kts) with 1-2 inches of precipitable water, increasing the chance of flash flooding from storms. Any storm is also capable of producing dangerous cloud-to-ground lightning.

I will continue to monitor the models and trends. For those of you in the mid-Atlantic States, there is more instability but less shear, so expect clusters of cells and a stronger squall line to organize.

Next entry: Tomorrow by 7:30 AM hopefully.

Acknowledgements: SPC Convective Outlooks and discussions with Steve Simon (grad student) & Scott Sieron (honors ugrad student).