textproduct: State College

WHAT HAS CHANGED

* Added details about this afternoon's severe threat. * Expanded discussion about frost/freeze potential through the weekend.

KEY MESSAGES

1) Wet Wednesday with widespread drenching rainfall and a few strong thunderstorms possible in southwest PA

2) Chilly pattern for the end of April with frost/freeze risk through the first weekend of May

DISCUSSION

KEY MESSAGE 1: Wet Wednesday with widespread drenching rainfall and a few strong thunderstorms possible in southwest PA

Extensive low clouds and ridge-shrouding/locally dense fog across CPA this morning. We added +FG at elevations AOA 2000ft based on blend of ASOS/RWIS data with visibility 0.5-1kft.

Drenching rainfall is expected to expand from southwest to northeast through the afternoon and evening before tapering off and shifting to the east late tonight into early Thursday morning. Rain may be heavy at times particularly across the NW Alleghenies with >1" amounts possible based on HREF/REFS PMM QPF signal. While largely beneficial especially in D1-D2 drought areas in the far southeast part of the CWA, some roadway ponding or minor low lying/poor drainage runoff issues are possible.

SPC has maintained a level 1/5 MRGL risk SWO across the Laurels, where SBCAPE values are between 500-1000 J/kg & 0-6 km shear is around 40-50 kts, with minimal instability east of the Laurels precluding any severe threat at this time. A messy storm mode is in place, with nearly saturated profiles up to 500 mb + upper-level divergence over the left exit region of a jet streak resulting in a mix of cells, clusters, and loosely-organized linear storm segments. Given the moisture in place, the threat for severe winds (>=58 kts) may be limited due to relatively warm cold-pool temperatures, though stronger cells & organized line segments may bring strong to locally severe wind gusts. A marginal threat of tornadoes is also in place, with decent 0-1km SRH (100-200 m2/s2) + meager CAPE hinting at the potential for low-topped supercells, though threat for tornadoes remains low given the environment. --------------------------------------------------------------

KEY MESSAGE 2: Chilly pattern for the end of April with frost/freeze risk through the first weekend of May

Several disturbances rotating around a persistent upper level closed low centered over Ontario and Quebec will help to reinforce broadly deep troughing across the eastern U.S. into next week. This pattern will keep conditions cool and unsettled with temperatures below seasonal norms. Chilly nighttime lows will also lead to frost and freeze concerns Thursday-Saturday night, particularly now that the growing season is now active across all CPA zones. Patchy frost may also develop across our far-northern counties tonight, but higher uncertainty exists given milder temperatures and mostly cloudy skies. For Thursday & Friday nights, frost/freeze chances are primarily north and west of I-80/I-99, with limiting factors being 850 mb temperatures a couple degrees warmer on those days + cloud cover Friday night limiting radiational cooling. Frost/freeze potential is highest Saturday night, with high pressure nosing in from the Tennessee Valley helping skies to clear and winds to lighten, with the greatest potential for frost/freeze north and west of I-78/I-81.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Light to moderate rain continues to move over the airspace bringing with it reduced visibilities and lowering ceilings. Most sites will remain IFR or lower tonight with high confidence (>90%) with ceilings behind the front expected to be less than 100ft AGL area wide. Conditions will begin to improve in the early morning hours on Thursday as winds shift to be more southwesterly. Drier air will be brought in at the surface and cloud decks will begin to scatter out around 12Z. Poor conditions will hold on longest over the northwest where BFD is expected to remain IFR into the early afternoon.

Winds could get gusty tomorrow afternoon as high pressure builds in the wake of the departing low. Winds could gust tomorrow afternoon up to 25kts. Dry weather is expected for all of Thursday afternoon before rain chances return Friday.

Outlook...

Thu... Drier conditions set in, mainly MVFR & VFR with BFD possibly having some IFR linger into the afternoon. VFR will be favored in the afternoon with many areas seeing decreasing cloud cover.

Fri-Sat...Mainly VFR with brief restrictions possible in showers.

Sun...Restrictions possible northwest in -RA and possibly some -SN.

Mon... Models hinting at another low pressure wave to our west, precip may lead to restrictions, particularly in the west.

CTP WATCHES/WARNINGS/ADVISORIES

None.