Friday Evening: MOD. RISK OF SEVERE T'STORMS SAT.

Synopsis:

A line of severe thunderstorms will be in western PA Saturday AM and move eastward, clearing PA by midnight thanks to a cold front. Additional storms in central and eastern PA ahead of the line cannot be ruled out. For Sunday, most locations in the Commonwealth will see a mix of clouds and sun, but the western half/ third of the State may get a shower from the upper-level low. High pressure builds in for next work week resulting in a cool-down under mostly sunny conditions. More details on the severe weather and cool-down follow.

Models Used: 01Z RAP (TwisterData), 00Z NAM (Hi-Res), 21Z SREF, 18Z GFS, 12Z ECMWF; Confidence Rating: STRONG (8/10).

Short-Term - Saturday & Sunday:

Instability: less than 500 J/kg in western PA; about 1000 J/kg in central PA; and 500-1000 J/kg in eastern PA... the latter area getting the storms later than everyone else.
Shear: moderate to high.
Moisture: high
Lifting: UL divergence, cold front

Scenario: Squall line, but UL divergence may lead to early convection in northern PA. No surprise but unlikely that 1300Z or 1630Z SPC outlooks place parts of PA/ NY in a high risk in areas where the UL divergence leads to additional storms. Most storms will produce lots of rain (up to 3/4 of an inch in some spots), dangerous lightning, and winds to 65 mph. Some storms in NE PA ahead of the line could produce lightning, additional rain, large hail and isolated tornadoes.

Sunday: The upper-level low will bring a shower to PA as the high is pretty far behind the front.

Long-Range - Next Work Week:

High pressure builds in. The 850-mb & 700-mb temps fall. The 500-mb trough is very amplified. A late-week recovery is expected a the 500-mb trough lifts north and east.

-Jaron Breen