textproduct: State College

WHAT HAS CHANGED

Thunderstorms have begun to develop in two areas of focus, ahead of the cold front in NW PA and along a stationary sfc trough in the southeast.

KEY MESSAGES

1) Scattered strong to severe thunderstorms this afternoon into tonight

2) Flooding downpours possible this afternoon into tonight in the Lower Susquehanna Valley

3) Variable sky conditions for the lunar eclipse tonight

DISCUSSION

KEY MESSAGE 1: Scattered strong to severe thunderstorms possible this afternoon into tonight.

Scattered thunderstorms are expected to continue to develop this afternoon ahead of a cold front across CPA and within a sfc pressure trough in the southeast. SPC has continued the level 2/5 (SLGT) severe t-storm risk which extends from the eastern slopes of the Allegheny Mtns eastward.

MLCAPE of 1500 J/kg and 0-6 km shear near 30 kts in the north suggests a few low end supercells may develop. Weaker shear and stronger CAPE in the SE suggests more pulse cells to start, but storm motion from SW to NE is well aligned with the sfc pressure trough so upscale growth into one or more slow moving / training lines is likely as we head into this evening. The strongest cells and clusters will be capable of producing scattered damaging winds and at least isolated hail. Modestly curved low- level hodographs may also support some brief tornado potential. The severe threat should persist into the evening before storms weaken/exit the eastern part of the CWA.

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KEY MESSAGE 2: Flooding downpours possible this afternoon into tonight across portions of the Lower Susquehanna Valley

A healthy influx of moisture via southwest flow will increase PWATs to 1.50-1.75" across the Lower Susquehanna Valley by this afternoon. CAMs suggest the heaviest 2-4+ inch rain amounts will remain east of the CWA, but still suggest local bullseyes of 1-2" in our southeastern zones along the weak pre frontal/lee sfc trough. A couple rounds of heavy t-storm downpours are possible with rain rates 1-2"/hr that could result in scattered areas of flash flooding. Based on the +RA signal in the hires ensembles and coordination with WFO PHI, a flash flood watch continues for Schuylkill, Lebanon, and Lancaster Counties.

A drying trend is forecast Friday into the last weekend of August, thanks to high pressure building into the area behind the cold front. This will likely setup a couple of foggy mornings (Friday and Saturday). Rainfall looks fairly limited heading into the first week of September; however despite the start of meteorological Fall the summer is not over with temps expected to rise above the historical average into the 80-90 degree range.

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KEY MESSAGE 3: Variable sky conditions for the lunar eclipse tonight.

Forecast viewing conditions for the lunar eclipse range from fair to poor tonight across central PA. The eclipse will begin at 10:34 pm EDT and last for about 3 hours, ending at 1:52 am EDT Friday. The worst view is most likely over the eastern half of CPA due to exiting storms and associated cloud cover. Clouds and low fog are also poised to develop in the NW during the latter half of the eclipse. The eclipse will take place during August's full moon, commonly referred to as the Sturgeon Moon. It will also be the last full moon of the summer with the next full moon set to rise a few nights after the autumnal (Fall) equinox on September 22nd.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Kept all sites with thunder Probs this afternoon, confidence is highest at MDT and LNS with higher storm coverage expected in eastern PA. Brief drops to IFR visibilities in these downpours along with gusty winds, possibly in excess of 40kts, may accompany these storms. Outside of storms, generally VFR conds for the remainder of the afternoon.

With high pressure building in the wake of the storms this afternoon, tonight into Friday morning looks to see fog and low ceilings building in, possibly into the LIFR category across the north and west. Region- wide restrictions into Friday morning are possible, trending towards VFR again late Fri afternoon through the remainder of the TAF period.

Outlook...

Sat...AM Fog; otherwise VFR.

Sun-Mon...Mainly VFR.

Tue...Chc afternoon SHRA/TSRA.

CTP WATCHES/WARNINGS/ADVISORIES

Flood Watch until 2 AM EDT Friday for PAZ058-059-066.