Area Forecast Discussion
Issued by NWS State College, PA

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253 FXUS61 KCTP 280907 AFDCTP Area Forecast Discussion National Weather Service State College PA 507 AM EDT THU JUL 28 2016 .SYNOPSIS... The stalled surface front over the Mason Dixon line will move northward today and tonight as a disturbance approaches from the Ohio and mid Tennessee River Valleys. This will produce a soaking rain over portions of central and south central PA tonight into Friday morning. Behind this system system slightly cooler air aloft moves over the region to usher in the weekend. But the ridge may begin to build to our west again early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Moisture and clouds continue to slowly increase from the southwest early this quasi stationary front near the Mason Dixon line begins to lift northward in response to approaching upstream troughing. Isolated showers are now lined up along the MD/WV/PA border and extend into portions of the Laurel Highlands and South Central Mountains...a sign of things to come later today and tonight. Deep layer moisture will continue to increase from south to north today as southerly component to 5h flow increases. Impressive moisture flux late this afternoon and evening will yield some 2.0"+ PW by this eve (00z Fri) and set the stage for some decent rainfall over the southern third to half of central PA overnight into Friday morning. Mins will generally range through the 60s across northern and central sections...except for the southeast which should bottom out around 70F. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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Impressive boundary layer convergence on the nose of a potent 40kt 850 mb jet will promote a well organized convective complex that traverses the southern third to half of central PA...with high confidence in a stripe of 1-2"+ rain totals by 15z Fri. Latest guidance has shifted the ribbon of max qpf slightly northward in proximity with the LLJ...and parts of the mid Susq River Valley may get in on the soaking rainfall late tonight and Friday morning. Areas well north of I80 may not see much...but pops still increase to high chc/likely late tonight and Friday with this wave. Flooding threat remains quite low, but WPC has placed my far southern and southeastern counties in SLGT risk (5-10%) of exceeding flash flood guidance. PHL and now LWX have issued Flash Flood Watches just south and east of my area, and day shift Thu may want to consider shifting north should latest northward model trend continue. For the remainder of Friday...expect only residual light scattered showers over mainly the higher terrain of the west and north as cooler air and slightly cyclonic flow come in the wake of the exiting shortwave. With abundant cloud cover and showers on Friday...highs will be cooler than recent days...and range from the upper 70s north to the lower to middle 80s southeast. Again...the bulk of the rain will come/wrap up by mid morning Friday...but far eastern sections may linger into Friday afternoon.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... In the medium to long-range period...conditions slowly revert to near normal in temp and precip as several chunks of short wave energy in the westerly flow aloft helps to carve out a mean 500 mb trough axis over the Glakes and Ohio Valley region during the Thu- Fri timeframe. The peak in unsettled weather (with perhaps some periods of down- right rainy conditions) occurs Thursday night and Friday as a well-defined wave of sfc-850 mb low pressure lifts ENE out of the Ohio Valley and heads across the I-95 Megalopolis. Followed a blend of EC/GEFS/superblend and NBM guidance for that particular 24-36 hour period to arrive at likely pops for rain and scattered TSRA. Some uncertainty in timing and areal coverage of the convection led us to undercut the NBM by 10-20 percent for now, recognizing issues with large scale model convective parameterization schemes (and subsequent exaggeration of the areal coverage and broader qpf amounts) means that we`ll likely see more concentrated areas/bands of heavy convection, compared to the model depicted, larger cold season stratiform look to the precip shield. Portions of Southern and Central PA...close to the track of the 1006-1008 mb sfc low will likely see some localized heavy 1-2 inch,12-24 hour rainfall amounts by Friday afternoon...with even the potential for some pinpoint heavier amounts from embedded TSRA, as a tongue of 2 inch pwat air lifts north and wraps cyclonically into sern PA and the Lower Susq Valley. For later Friday through the upcoming weekend, a large area of high pressure (1020-1024 mb) near the border of southern Quebec and Ontario will try to push drier air south into the Mid Atlantic Region. Another...apparently weaker wave of low pressure at the sfc and aloft lifts NE out of the Ohio Valley over the weekend and brings an enhanced chc for showers. Slight diffs in timing/location exist between the EC/GEFS and NBM guidance. However...the target period for the best chc of showers and isolated to sctd TSRA appears to be late Sat into Sunday. Afterward, heights begin to rise from the southwest, accompanied by a ridge of surface high pressure building east into PA with mainly dry conditions and a rebound in temps for early next week. && .AVIATION /09Z THURSDAY THROUGH MONDAY/... 06Z TAFS sent. Some mid and high clds across the sw. Isolated showers along the MD line. Earlier discussion below. VFR conditions across the region this evening. Expecting some fog to develop overnight...affecting most airfields with MVFR conditions. IFR conditions were introduced int KBFD TAF, following the lead of what`s happened there for the last several nights, with a low IFR stratus deck developing in the pre-dawn hours. Morning fog/haze will lift early Thursday. Showers and isolated thunderstorms could move into the area from the southwest. With POPs generally less than 50 percent, and scattered nature of the rain, have left out of TAFs except for a VCSH in KJST for now. More restrictions possible overnight Thursday into Friday with the potential for rain and thunderstorms along with fog. Conditions expected to improve Friday into the weekend. OUTLOOK... FRI...Some restrictions in SHRA/TSRA and patchy fog...mainly early. SAT-MON...Wide range of conditions expected with a chance of showers and storms. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...DeVoir SHORT TERM...DeVoir LONG TERM...Lambert/Gartner AVIATION...Jung/Martin is the U.S. government's official web portal to all federal, state and local government web resources and services.