textproduct: State College

WHAT HAS CHANGED

*Increasing confidence in the return of hot and humid pattern for the middle of next week

KEY MESSAGES

1) Elevated flash flood risk through this evening

2) Hot and humid pattern set to return for the middle of next week

DISCUSSION

KEY MESSAGE 1: Elevated flash flood risk through this evening

Scattered thunderstorms have increased in earnest in response to surface heating and destabilization. Locally heavy rainfall is contributing to flash flood potential that should continue through 00Z/8p this evening.

The storms are located in several clusters from northwestern Ohio through central Pennsylvania. The storms are located south of a front over Lake Erie and are in an airmass characterized by 1.5-1.8 inch PW values and ~2000 J/kg MLCAPE, supporting robust updrafts with locally heavy rainfall. MRMS estimated of 1-1.5 inch/hr have already been noted, which isn't surprising given modest steering flow aloft (supporting 10-20 kt storm movement). Flash flooding is likely on at least an isolated basis in the short term - especially in spots of highly sensitive to compromised soils in complex terrain with FFG thresholds below 1 inch/hr.

The ongoing flash flood risk focused primarily over west-central PA will continue to expand slightly eastward in response to peak heating/destabilization through the afternoon. The risk will primarily be diurnally driven and may lessen gradually with loss of surface heating after sunset. Isolated to scattered instances of flash flooding are expected, with several areas of storm cell mergers supporting local peaks of 2 inch/hr rain rates and spots of 3 inch rainfall totals.

While the primary threat with storms this afternoon will be locally heavy rain and flash flood potential, we still can't rule out an occasional strong to locally damaging wind gust.

Focus for locally heavy t-storms shifts to the southern half to 1/3 of central PA on Saturday. Meanwhile, much drier/less humid air will filter into northern PA and be a harbinger for a more pleasant end to the weekend/start to next week.

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KEY MESSAGE 2: Hot and humid pattern set to return for the middle of next week

Dry conditions are expected to prevail for the first half of the week with a strong ridge expected to develop over the middle of the country. Increasing heat/humidity is forecast across central Pennsylvania although there remains some uncertainty with respect to how warm temperatures and/or humidity get across the region. Current forecast favors the hottest temps returning Tue to Thu with highs 85-95F and max heat index 90-100F. Rain chances increase into the latter half of the week.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Similar to yesterday, convective activity will downtrend over the next few hours as the sun sets. Scattered showers/storms will continue to focus primarily around a quasi-stationary front across the Northern Tier (KBFD) over the next few hours, with spottier activity expected elsewhere given convective overturning in the wake of the earlier storms. Otherwise, mostly cloudy skies will persist tonight, with areas of fog and low stratus once again expected overnight due to recent rainfall & the warm/muggy air mass in place.

Gradual improvements to VFR are expected Saturday morning as diurnal mixing deepens the boundary layer, with intermittent MVFR/IFR ceilings possible as low stratus lifts and transitions into a cumulus field. Regarding convective activity, a positively tilted trough nosing in from the northeast will tend to shunt showers/storms to our south where a shortwave will once again be moving across the Mid-Atlantic. With that said, convergence between a surface low over NJ & the front draped across the Northern Tier may serve as a focus for scattered showers and thunderstorms over eastern Pennsylvania (KIPT/KMDT/KLNS) during the afternoon. Higher confidence in convection is closer to the surface low (east of KIPT/KMDT/KLNS), with isolated showers/thunderstorms expected elsewhere across the Commonwealth as the front drifts southward.

Outlook...

Sun-Wed...Mainly VFR with areas of late night/AM fog.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch until 10 PM EDT this evening for PAZ010-011- 017>019-024>026-033-034.