Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 260045 AFDCTP Area Forecast Discussion National Weather Service State College PA 845 PM EDT Thu May 25 2017 .SYNOPSIS... Mostly cloudy skies with scattered showers and isolated thunderstorms will persist into the evening hours. A few strong thunderstorms are possible, mainly across south- central and southwestern PA. Scattered showers will linger into Friday followed by a period of mainly dry conditions Friday night into Saturday. Showers and thunderstorms will likely impact the area Sunday into Memorial Day. Today will be the coolest day this week with temperatures rebounding through the holiday weekend. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Back end of double barreled surface low pressure system will lift north through the area overnight. Sfc cyclonic flow under cold upper core aloft will support scattered rain showers and isolated thunderstorms into the early overnight, especially western sections early this evening. Some areas of heavy rain this evening will decrease by late evening. Srn third to half of the CWA remains in a Marginal outlook for severe thunderstorms through this evening...with local heavy rain threat being monitored as well through late evening. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Broad cyclonic/west-northwest flow on southern end of exiting upper trough will support terrain-enhanced showers on Friday before precip winds down Friday night/AM Saturday. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... A lower-amplitude but moderately strong westerly (zonal) mid level flow will set up in the wake of the departing upper trough with modest height rises/weak will ridging aloft into the weekend. A warm front is progged to extend east from surface low in the western Ohio Valley to the mid-Atlantic coast on Saturday. Central PA should reside on the north/east fringe of high instability convective corridor/MCS type pattern expected to evolve from the central and southern Plains to the southern mid- Atlantic coast into Saturday night. The greatest risk for scattered thunderstorms remains over the SW 1/3 of the CWA which is consistent with previous fcsts. SPC has introduced a MRGL risk into this area for D3. The remainder of the area should see a mainly dry start to the holiday weekend but will maintain slight chance POPs. The large scale pattern will evolve into a broadly cyclonic flow regime by Monday with upper trough parked over the Great Lakes and southeast Canada into midweek. The aforementioned warm front will lift north across the area on Sunday followed by a series of weaker cold front associated with shortwave trough rotating around parent upper low centered to the south of Hudson Bay. Ensemble blend still supports max POPs on Sunday/Sunday night into Monday with some additional shower opportunities into midweek as series of shortwaves rotate around mean upper trough. Temps should average pretty close to normal/seasonal to close out the month of May. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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Meso anal shows 2 surface lows, one over NW PA and another down over the northern Chesapeake. The water vapor loop shows a potent shortwave rotating around the parent upper low which is near the MD/WV panhandles. Modest instability that had developed over southern areas is now fading with the loss of heating. There is still some potent shear over the far SE of the forecast area so the storms rotating up out of MD need to be watched for the potential of a strong wind gust and/or a downpour, but the trend will be the severe threat to fade and the heavy rain threat to shift east as the evening progresses. A second line of convection has formed and extends from northern Cambria country down to about Bedford and southward. AOO looks the most vulnerable over the next hour to see brief restrictions as these showers and storms move east through the terminal. The bigger picture shows most terminals VFR, but with the upper low expected to pivot over the state during the evening and overnight, widespread MVFR/IFR can be expected to redevelop. Cooler air advecting in aloft, combined with deep moisture and a favorable westerly upslope component over the Western higher elevations will lead to IFR/LIFR conditions at KJST and KBFD. Across eastern Pa, light wind, wet ground and light winds could result in areas of forming late tonight. After some areas of low cigs and fog early in the day Friday, the afternoon will feature mainly VFR with brief MVFR/IFR in isolated-scattered showers...mainly after 16Z. Moist WNW upslope flow will continue across the western mountains with the best potential for lingering reduced conditions and scattered showers. .OUTLOOK... Sat...AM fog possible BFD. Sun...Showers/reduced cigs possible, esp Sun night. Mon and Tue...AM low cigs poss west. Sct PM tsra impacts poss east.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Gartner NEAR TERM...DeVoir/Gartner SHORT TERM...Steinbugl LONG TERM...RXR/Steinbugl AVIATION...La Corte

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