Area Forecast Discussion
Issued by NWS State College, PA

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658 FXUS61 KCTP 192052 AFDCTP Area Forecast Discussion National Weather Service State College PA 352 PM EST Thu Jan 19 2017 .SYNOPSIS... High pressure overhead will retreat and a warm front will push rain across the state on Friday. Relatively mild conditions will persist for the next several days. A very complicated storm system may bring a prolonged period of rain from Sunday into early next week. Snow or mixed precipitation is also possible from that same storm early next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Clouds breaking up now - esp so in the S. This trend should continue but the nrn mtns may stay cloudy longest this evening. In a tricky part of the forecast, some low clouds may form again later tonight on the higher elevations as SE flow begins ahead of the warm front approaching. However, the overall cloud forecast is generally cloudy tonight with high clouds over the area. As the low levels stay generally clear, the temps may cool to below freezing in spots like FIG, MUI, THV, and lots of the area N of IPT. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Warm frontal precip moves in Fri morning around sunrise or a little later in the Laurels and spreads a band of 3-6hr light rainfall across the entire area during the daylight hours. Timing is very solid amongst all models and forecast confidence is very high. There is one very small trouble with the rain - if it moves in quickly enough to get to some of those patches where it will be below freezing, there might be some fzra. However, most of the places which may dip below freezing will have a bit of daylight to help it warm up slightly. Also, the wet-bulb effect could present a minute chance of it freezing up - mainly over the NE - but again, those areas should have the chance to warm up enough to keep the fzra threat low. Have not put the mention in the grids yet. Maxes/diurnal swing will be held down once again by the cool air trapped and not quite get into the 40s over a good portion of the area - with mid 30s the expectation in the NE and the central mtns. Even MDT and LNS may not eclipse 40F. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... The upper ridge is forecast to re-establish itself over the eastern U.S. over the upcoming weekend, bringing mild and mainly dry conditions Saturday, through at least the mid morning hours on Sunday. Daytime temperatures across most of Central Pennsylvania will be well above normal, but the departures for overnight lows should be greater by several degrees more throughout the entire extended period. The ridge axis will shift to the Hudson Valley and Eastern Seaboard early Sunday as a sfc backdoor cold front drifts swwd into PA and stalls out as a potent and moisture laden nearly stacked low lifts NE from the deep south to the Delmarva region by 12Z Tuesday. Temps could be marginal at the start of pcpn overnight Sunday for some ice or snow, and soundings via the GFS/GEFS and EC appear cold enough for Sunday night through Monday night for a mix of rain/snow (or even periods of all wet snow at times across the northern mtns of PA). However, the bulk of pcpn across the Central Ridge and Valley Region looks to be rain at this point through Monday afternoon. The trend in most operational models and ensembles has been further to the south and east with this particular late weekend/early week system. This places parts of the fcst area in the sweet spot for potentially several inches or more of heavy, wet snow (especially later Monday/Monday night across the nrn and wrn mtns of PA at elevations of 1400 ft or higher), as the mean 850 mb low in the GEFS and EC tracks NE along the I-95 corridor in VA and adjacent SERN PA/Southern NJ. U-wind anomaly at 850 mb peaks at -4 to -5 sigma during much of Monday as a 45-55kt easterly llj develops between this approaching low, and the aforementioned colder airmass pushing swwd from SERN Canada and the New England states. Rainfall amounts are expected to be in the 1 - 1.5 inch range across roughly the SE half of PA with lesser amounts to the NW. Another short wave ridge will slide east from the Ohio Valley and move over the Commonwealth Wednesday, accompanied by light wind and fair/generally dry conditions. && .AVIATION /21Z THURSDAY THROUGH TUESDAY/... High pressure trying it`s best to clear things out as the inversion lowers into the evening. However, the low clouds may return to the higher elev sites later tonight as a light SE flow ensues ahead of the warm front. The warm front will bring lowering clouds from high-mid-low as it approaches anyway. But the low clouds may form aside from that more obvious progression. Timing from all models is nearly identical and leads to very high confidence forecast of rain timing, beginning about 13z in JST and 17Z in MDT & IPT. There could be a brief period of IFR at all sites, but esp JST/BFD. The WAA rainfall passes by 18Z in JST and by 00Z Sat at IPT. However, low clouds and patches/widespread drizzle are expected as the moist air sits over the mountains. Outlook... Sat...MVFR cigs W/VFR cigs elsewhere. Sun...Widespread IFR/MVFR restrictions - mainly S. RA advances fm S-N. Mon-Tue ...Widespread IFR restrictions in -RA and poss SN on higher elevations. LLWS poss. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...Lambert/Gartner AVIATION...Dangelo is the U.S. government's official web portal to all federal, state and local government web resources and services.