Area Forecast Discussion
Issued by NWS State College, PA

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399 FXUS61 KCTP 212320 AFDCTP Area Forecast Discussion National Weather Service State College PA 720 PM EDT Fri Jul 21 2017 .SYNOPSIS... Pennsylvania will be on the northern periphery of a subtropical ridge passing across the southern states through the weekend. A few rounds of showers and thunderstorms are expected both Saturday and Sunday, and some could produce gusty winds, hail and heavy downpours. Another cold front will push through the area early next week. && .NEAR TERM /UNTIL 7 AM SATURDAY MORNING/...
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Convection all but dead. Just a hint of taller cu in the far srn tier, and the 20 POPs there will expire in an hour or so - right on time. Other than the high clouds in the N, clearing should come to much of the area shortly. Prev... Weakening MCS traversing WV and approaching the WV and MD panhandles at mid afternoon. PW pooling around 2" along the Mason Dixon line and slowly lifting northward should bring isolated to scattered coverage of showers and thunderstorms through this evening across my southern tier counties (Laurel Highlands and South Central Mountains), with mainly dry conditions expected elsewhere. remnants of aforementioned MCS track off the mid Atlantic coastline later this evening, and any diurnally-driven showers or storms along the southern tier should die out around sunset. Weak surface ridge passes over PA tonight bringing fair weather and mins ranging from the upper 50s north to around 70 southeast.
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&& .SHORT TERM /7 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Large MCS forms upstream overnight and approaches eastern OH in the pre dawn hours Saturday morning. This feature will be the main player for potential severe weather on Saturday, as strong moisture flux and increasing boundary layer convergence point increase the likelihood of strong to severe storms over PA by late morning and afternoon. CAMs differ on timing and strength of MCS evolution ranging from as early as late morning into my western zones to as late as mid to late afternoon. Think the former is more likely...given quick moisture return late tonight and Saturday ahead of the approaching complex. Warm front pushing into the region on Saturday will also tend to favor lower LCLs and sufficient shear for rotating updrafts. Farther north, extensive cloud cover associated with the warm front will likely result in limited CAPE Saturday as the 00Z GEFS shows. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... A second round of convection is possible Sat night as strong low level jet and plume of anomalous PWATs works through the area. Convection associated with this feature could potentially evolve into another MCS with potential for overnight severe weather in central PA into Sunday morning. Favorable scenario for additional severe weather across central Pa during the daylight hours Sunday as the region will be within warm sector south of anomalous surface low tracking eastward along the PA/NY border. Moderate CAPES and moderate westerly flow aloft, combined with large scale forcing ahead of approaching upper trough, should support widespread convection by afternoon. Some uncertainty continues with regards to timing of upper trough passage early next week, but additional showers/storms appear possible. A period of dry and cooler weather appears very likely by midweek, as upper trough axis finally passes east of Pa and surface high builds into the area. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/... Large scale subsidence bringing a rain-free afternoon for most, though slight chance for an afternoon thunderstorm will persist across southern mtns in deeper moisture. Quiet night tonight, with most locales remaining VFR, though the usual spiderweb of valley fog will settle into the western and northern mtns. Warm front pushes into the region on Sat followed by an upper trough on Sun, which will keep numerous showers and thunderstorms around over the weekend. .OUTLOOK... Sat...AM valley fog possible. TSRA/SHRA likely with intermittent impacts. Sun...AM valley fog likely. Cig restrictions likely north. TSRA/SHRA likely with intermittent impacts. Sun night...Cig restrictions likely. Scattered TSRA/SHRA. Mon...AM restrictions likely. Scattered TSRA. Tue-Wed...Patchy AM fog. Otherwise no sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...Dangelo/DeVoir SHORT TERM...DeVoir LONG TERM...Fitzgerald/Gartner AVIATION...Jung/DeVoir/RXR

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