Thursday, May 31, 2012

Risk for Severe Weather Friday Evening

By early June standards, the storm system that's responsible for our next chances of storms is rather potent and one that's more typical for April in terms of energy and intensity. Yesterday, it did its dirty work across the Plains and will impact the Mississippi and Ohio Valleys today.  Tomorrow, it's got its sights set on the East Coast and the potential for a decent severe weather outbreak for Pennsylvania through South Carolina are in the cards.

There is a good bit of dynamic energy with this storm system, which fueled with a decent amount of instability should be enough of a trigger to get a line of thunderstorms to march in from the southwest during Friday afternoon and continuing through Friday evening.  A slight risk of severe weather is out from Pennsylvania south through Georgia with South Central Pennsylvania, Maryland, Virginia, and portions of the Carolinas in an areas of higher risk (30% chance as of this morning) to see at least some severe weather tomorrow.  Locally, we're in a slight risk...and with the timing of this event focusing more on Friday evening and less on the afternoon hours here I wouldn't be surprised if our odds for severe weather end up a bit lower in the city than farther west as storms move through those areas earlier in the day.  How much severe weather we ultimately get here depends on sunshine during Friday as well as whether the surface warm front is able to get far enough north to get us into a more unstable airmass.  As of now, areas west of us stand a better chance of getting the instability needed to fire up severe weather.

Any storm that does fire has the potential of large hail, gusty winds, and perhaps a tornado.

Besides severe weather, the potential for more localized heavy rainfall will exist with this storm system.  The NAM (below) shows the potential for some areas to the city's west picking up over an inch of rain, with the highest rainfall totals over the mountains and hills in Central and Northern Pennsylvania.  The city and points south and east may not see a ton of rain with this system as storms associated with the low weaken a bit as they move through Friday night.  However, if the more robust severe setup takes hold we could see some localized one inch rainfall amounts in or close to the city.
Timing this out, it looks like Central Pennsylvania should see thunderstorms in the mid to late afternoon, with the threat shifting into the Philadelphia region during the evening (after 7 or 8 PM).  Of course, timing will nudge around a bit over the next day or so but it appears this storm system is more an evening/nighttime issue in Philly and points east.