Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 261359 AFDCTP Area Forecast Discussion National Weather Service State College PA 959 AM EDT Wed Apr 26 2017 .SYNOPSIS... A moist east-northeast inflow from the Atlantic Ocean will provide a cloudy and misty start today, followed by clearing through the afternoon. A few strong to severe storms are possible across the Northwest Alleghenies Thursday afternoon and evening. Warmer temperatures are expected through the end of the week. && .NEAR TERM /THROUGH TONIGHT/... GOES-16 shows the closed low circulation south of Long Island. Vertically stacked system slowly drifting to the north. A trough extends back over us. Lucky us! Clear skies to our west and low clouds stuck over our region and at least two distinct wrap around high cloud bands above the low clouds. Not much on radar. The HRRR implies the sun will erode the clouds. Areas between bands and farther west will see peaks of sun. This will increase as the day goes on. The HRRR and SREF have only slight chances of any showers this morning in southeast PA close to the last band seen on radar earlier today. Kept the patchy fog in southern PA through this AM. Probably patchy drizzle in a few places too. But this should steadily erode. Warmer we get this afternoon the more we will erode the clouds and temperatures should rebound with late afternoon highs probably in the 70s in many locations. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Overnight still some lingering clouds. We should see a surge of warm air into the region. Most guidance shows 15-18C at 850 hPa implying a well above normal day temperature-wise. But the front to our west is trying to move into the western flanks of the ridge. Thus the GEFS and SREF generate some CAPE and there is a modest surge of wind into westernmost PA. Thus Marginal risk in western PA. The SREF/GEFS timing is pretty late in the afternoon and evening. GEFS clearly generates QPF in afternoon and evening with EFS mean CAPE generally in the 600-1000JKG-1 range moving by. Thus both systems general QPF/POP mainly after 21Z in western PA which moves into central areas after 0000 UTC. This implies these EFSs release the CAPE so to speak and imply convection mainly in the 21 to 03 UTC timeframe. Drier air as indicated in the PW field implies sweeps across the State west to east in the 0000 to 0600 UTC range implying similar timing as the POP/CAPE maximums. Not big event. But good chance of thunderstorms in northwestern PA and at least a chance in central areas. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Model and ensemble guidance remained in good agreement with large scale pattern amplification this period with a vigorous closed H5 low ejecting northeast from the southern Rockies into the upper Great Lakes/Canada and deep surface cyclone expected to lift out of the MS Valley. Meanwhile, an anomalous upper ridge centered over the Southeast U.S./western Atlantic will gradually weaken and shift east. The details of weekend forecast are still uncertain with rain risk likely focusing along/north of quasi-stationary frontal zone progged to shift south of PA by early Sunday before lifting back to the north as warm front. Therefore continued to utilize a NBM/ECENS/WPC blend for max/min temps and POPS which maintained good continuity with previous fcst. While unsettled with a period of rain likely at some point, the fcst does not look like a washout. Temperatures should remain above late- April climo but could be too warm/cool depending what side of the boundary you are on. Max POPS remain centered on Monday/May 1st as the aforementioned cold front crosses the Appalachians and continues toward the Atlantic seaboard. A severe weather threat may evolve downstream from the OH Valley into the Mid Atlantic, but at this time it is unclear whether instability will be sufficient to support severe storm risk. Temperatures will decline to near normal behind the cold front by next Tuesday May 2nd. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... The focus of moist and rather deep east to northeasterly flow off the Atlantic, in conjunction with low pressure lifting north from the Delaware coast, will maintain IFR to LIFR cigs into the late morning hours today (based on SREF Prob charts) with areas of MVFR to IFR Vsbys in -DZ and BR (especially over the east facing slopes and crests of the ridges). The early low CIGs/area of light rain and drizzle across the Susq Valley and points east will give way to gradually improving conditions during the late morning and afternoon hours today, as the storm system weakens and moves northeast twd Cape Cod. Model RH profile support VFR conditions at BFD/JST by midday, while more gradual clearing takes place across the eastern half of the state during the afternoon. Poorest flying conditions will likely hang on the longest (perhaps until 16-17Z) across the Lower Susq Valley invof KMDT, KLNS and KMUI. Outlook... Thu...AM fog possible. Isolated PM tsra impacts possible west. Fri...No sig wx expected. Sat...Rain/low CIGs possible NW Mtns. Isolated tsra impacts possible southeast. Sun...Low CIGs possible east. Isolated PM tsra impacts possible west. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Grumm SHORT TERM...Grumm/Steinbugl LONG TERM...Steinbugl AVIATION...Lambert

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