textproduct: State College

WHAT HAS CHANGED

* Issued a Flood Watch (4 PM today to 4 AM Sunday)for the potential of locally up to 2-4 inches of rain and Flash Flooding.

KEY MESSAGES

1) Numerous showers and thunderstorms developing over/moving into the NW Mtns and Laurel Highlands could bring locally over 2 inches of rain and some areas of flash flooding late today into early Sunday.

DISCUSSION

KEY MESSAGE 1: Numerous showers and thunderstorms developing over/moving into the NW Mtns and Laurel Highlands could bring locally over 2 inches of rain and some areas of flash flooding late today into early Sunday.

A juicy airmass (with PWAT values peaking between 1.5 and 2 inches), a prominent zone/axis of llvl streamline/theta-E convergence and the eastern edge of moderately high MU CAPE values over 1000 J/KG will focus the heaviest rain over the next 18-24 hours across the Laurel Highlands and NW Mtns. The past several runs of the HREF and its high res members have been homing in on our western zones with 6 hour PMM values of 2-3+ inches, which is near or slightly hours than 6 hour FFG values.

Previous...

Expect showers and storms to form later this afternoon into Sunday morning, as warm advection brings back the aforementioned, much more humid airmass.

This will be followed by more showers and storms later Sunday afternoon and evening, as stronger dynamics and cold front work on the humid airmass.

Not a lot cold advection, abnormally warm and moist air take aim at the Great Lakes area again on Tuesday, as a strong upper level ridge builds northward from the TN Vly.

ERO for today adjusted to one area, and SPC outlook for Sunday trimmed across the southeast. Complex fcst, as been the case this summer.

Still holding off on a flood watch for now, given nothing going on yet on radar, still time to see how things play out later this aft.

More information below.

Guidance does put numerous heavy bands of rain over the area. FFG lower west and north, but heaviest QPF could be to the east. Also maybe things more an issue later Sunday, depending on where that rain falls today.

Again, the problem is: where? With uncertainty high as it is and FFG getting higher slowly, still holding off.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Moisture is streaming in from the south early this afternoon (PWATs 1.5-2"), leading to MVFR ceilings remaining in place along and around the Allegheny front. An area of clearing in southwest PA is slowly eroding away at this lower ceiling deck which may lift terminals like JST and UNV to VFR in the coming hours. Cloudy conditions will likely remain across most other terminals though ahead of precipitation this evening.

Building instability from the aforementioned area of clearing will allow for thunderstorm development in the 20Z-22Z timeframe in Western PA. Have adjusted PROB30 groups to reflect latest confidence in timing of potential airfield impacts. Given the scattered, possibly repeating, nature of these storms, uncertainty in exact timing is still high enough to not include any TEMPO groups at this time.

The best overlap of instability and high PWATs appears to be at BFD, JST, and AOO. This is where the strongest storms with the heaviest rainfall, gusty winds, and visibility impacts are likeliest. Given the cloudier conditions further east limiting instability growth, showers and thunderstorms' are expected to be weaker. Some heavy downpours remain possible after sunset though given the high PWATs, so included visibility restrictions PROB30s elsewhere too.

The influx of low level moisture will also contribute to low ceilings tonight. Included prevailing IFR ceilings at all TAF sites in the wake of storms and showers moving through. Heaviest restrictions are most likely to come in the form of low ceilings and mist with for the most part with low ceilings lasting into tomorrow morning. However, clearing skies around sunrise at BFD, JST, and AOO may lead to some fog development early tomorrow morning.

Outlook...

Sun...Early MVFR/IFR and moderate rainshowers across the state. Additional SHRA/TSRA in the afternoon.

Mon...Primarily VFR conditions, with some potential for afternoon SHRA/TSRA.

Tue-Thur...Mainly VFR with a showers possible over NW PA.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch through late tonight for PAZ004-005-010-011-017- 024-033.