textproduct: State College

WHAT HAS CHANGED

* Tweak PoPs and Sky cover today, and added patchy, mainly valley, fog to this AM and Fri AM wx grids.

KEY MESSAGES

1) Showers and perhaps a thunderstorm are possible over the southern tier of PA today and this evening. Dry conditions for Friday before an unsettled weekend.

DISCUSSION

KEY MESSAGE 1: Showers and perhaps a thunderstorm are possible over the southern tier of PA today and this evening. Dry conditions for Friday before an unsettled weekend.

Clouds are trying to clear out over the north, so we've added patchy fog to the river valleys there and in the central mountains as we/they may clear up better than the south by morning.

The cold front won't likely pass through until the evening, so there will be additional SHRA today with up to 60 pct in Somerset Co. A stray shower (no thunder) could also affect Warren/McKean Cos as the cool air aloft helps create some very weak instability along the NY border and the cold front passes. However, instability over the CWA will be low (<500J/kg in the far SW), so only some isolated thunder is expected - and only in the Laurels. The risk for heavy rain has decreased markedly through the last 48 hrs of model runs, and the WPC ERO MRGL risk area won't touch PA anymore (stays to our S) with the new guidance to be issued soon. The most-possible time for rain will be the afternoon and early evening as some of the weak convection moves in from the SW. The dewpoints don't come down until the front arrives (mid-late morning N, close to sunset in the S). So, it may still feel a little muggy today, esp from I-80 southward with 65-70F Tds all day long.

High pressure builds behind the cold front, giving way to a dry and mainly sunny Friday. AM valley fog is almost a given. The extent of the fog is a question, but we'll paint it in all the normal nrn valleys at this point. Low level moisture lurking just south of the Mason/Dixon line Fri night will advance NE across the state on Saturday as SFC high pressure moves well off the Mid Atlantic and Southern New England Coast. This will lead to some showers spreading NE across the region with a few PM TSRA possible Saturday and/or Sunday afternoons, especially over the western mtns. A more-active (wetter) pattern is in store for Mon-Tues. But, the flat upper ridge over the southern half of the CONUS will make it difficult for deep moisture to make it into PA ahead of any shots of atmos forcing. The week could end dry as the upper ridge pumps up over the central CONUS.

AVIATION /06Z THURSDAY THROUGH MONDAY/

A SW-NE axis of scattered SHRA associated with a pre-frontal trough will continue progressing eastward across the Commonwealth through the overnight hours. MUCAPE has downtrended to ~250 J/kg over the past hours, with lightning becoming less likely over central PA as activity gradually wanes in coverage/strength. Gusty SW winds of around 15-20 kts may precede and accompany these showers, especially around the weak remnant MCV towards KJST/KAOO (KJST gusted to 26 kts from 250 deg at 4:58Z), with lower confidence with eastward extent into KAOO/KMDT/KLNS given weakening presentation on base reflectivity and velocity. Otherwise, areas of low stratus in the wake of this rainfall may bring periodic restrictions overnight, with higher confidence in prevailing restrictions at KBFD/KJST due to upslope westerly flow.

Cloud ceilings will gradually lift through the morning hours and into the afternoon, with intermittent MVFR ceilings possible given low-level moisture from air mass + recent rainfall as the boundary layer mixes out and deepens. Westerly winds will increase to around 10 kts during the late morning and through the evening as a cold front approaches from the north, with gusts of around 15-20 kts expected throughout the daytime. A few showers may develop as well given the approaching front (10-20% chance), though more numerous SHRA and a few TSRA are favored farther south across the Mid-Atlantic associated with the pre-frontal trough.

Winds will trend light and variable Thursday night as high pressure moves in from the southern Great Lakes, with background flow tending northerly through the night as the cold front moves north-to-south through the region. Clearing skies behind the front paired with light winds under high pressure will favor areas of radiation fog overnight, primarily outside of the Lower Susquehanna Valley (KMDT/KLNS) where mid-level clouds ahead of the front may linger & mitigate fog development.

Outlook...

Fri...VFR conditions expected.

Sat-Mon...Primarily VFR conditions, with some potential for afternoon SHRA/TSRA on at least a hit and miss basis.

CTP WATCHES/WARNINGS/ADVISORIES

None.