Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291205 AFDCTP Area Forecast Discussion National Weather Service State College PA 805 AM EDT Sat Apr 29 2017 .SYNOPSIS... A nearly stationary frontal boundary will be located over portions of Pennsylvania for much of the time this weekend. A few disturbances aloft will move over this front and bring periods of showers and thunderstorms. A strong trough and cold front will move across the region on Monday, followed by much cooler temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Fast-moving and the northeast member of a series of MCSs (that stretched all the way back to the southern plains) has exited our CWA and is heading quickly for the NJ coast. Another batch of showers and perhaps a few rumbles of thunder will affect far southern and western parts of the CWA during the late morning hours as it races ENE and temporarily weakens. Low temps around sunrise will range from the lower and mid 50s across the NW half of the forecast area...to the mid 60s across the Lower Susq Valley (that current lies close to the quasi- stnry frontal boundary). These temps will be about 15-18 deg F above normal. First front, separating the very warm and juicy airmass (where temps will be in the 80s with dewpoints in the mid 60-lower 70s this afternoon) extended from central WVA to extreme SE PA and will be drifting a little further south into northern VA late this morning. A second (cold front) extended from western Lake Ontario Lake Erie and will be sliding into our far nrn zones during the late morning and afternoon, with the central third of the state sandwiched in between (in the Temperate Zone). For the late morning and afternoon hours, the HRRR shows a few weak sfc waves sliding east across the region about 30-50NM south of the I-80 corridor. Marginal Risk for SVR TSRA across the northern half of the CWA looks to be overdone, with any thunder across that region coming in the form of elevated weak- mdt instability. 00Z-06Z NAM has trended at least 50-75NM further south with significant sfc based cape and better low-mid level directional shear and EHIs, so the main threat for any localized strong to potential SVR tsra will likely be across the southern 1-2 layers of PA counties. Max temps are a blend of the more heavily weighted 29/06Z NAM (70 percent) with about 30 percent 29/00Z Nat`l Blend of Models. More singular nudging/weighting twd the NAM results in quite chilly temps in the upper 50s to lower 60s across the nrn tier counties of PA. Don`t want to jump the gun and go that low just yet, but it`s pretty obvious that if the cooler models verify better, it`ll be too cool/stable for significant/strong convection. Potential for locally heavy rain of an inch or so may be a different story across roughly the SW half to two thirds of the CWA as more organized convection and another possible MCS rides ENE across the aforementioned stalled out pair of sfc-925 mb frontal boundaries. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... 29/06Z NAM guidance brings both of the previously noted frontal boundaries gradually back to the north overnight and Sunday, but maintains shallow chilly air across the Central and NE zones as the elongated east/west 1022-1026 mb sfc ridge slides over the middle St Lawrence River Valley by Sunday afternoon. Again, the main focus for Sunday may be periods of heavy rain showers/TSRA from elevated convection, while any sfc-based updrafts stay limited to the south central counties and wrn mtns near and to the west of RT 219. Sunday`s max temps will also be weighted more heavily twd the cooler 29/06Z NAM with a 25 percent NBM blend afterward, which will lead to highs in the mid to upper 70s over the west and south, and only low-mid 60s in the far NE and wrn Poconos. With dewpoints well up into the 60s over far southern and western portions of the CWA, it will begin to feel humid. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Upper level ridge builds across the Mid Atl Region Sunday night and Monday and a warm front will be lifting through the Ohio Valley and W PA. This weather feature will lead to continued chances for showers and even a tsra - mainly in the NW half of the area. Temps should return/rise to very very warm levels on Monday. A massive and deepening cyclone lifting into the western Great Lakes Sun night into Monday will push a strong cold front through PA Mon into Mon night, accompanied by a round of potentially potent showers and thunderstorms (likely reaching western half of CWA in the afternoon and eastern half during the evening). Once this front passes by much chillier air will advect into PA on cyclonic flow with unsettled light showery weather persisting mainly for the northern part of the state right into Wednesday. Chance for a more widespread light rain arrives Thu into Fri as a low progged to develop along the southern Appalachians and lift northward. Models showing strength/timing issues so not getting to specific this far out, but looks like unsettled weather pattern continues. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... The next wave of high-based showers and embedded tstms will track across southern PA this morning. MVFR/IFR visibility at MDT/LNS should improve with the onset of pcpn btwn 13-14z. 29/12z TAFs continued to rely on persistence, radar trends and high res model consensus which still favors a predominately VFR fcst at least through the first 1/2 of today. A quasi- stationary frontal boundary will bisect the airspace by this evening with MVFR cigs likely on the northwest side. Confidence is low concerning pcpn trends for the afternoon but consensus suggests isolated convection confined mainly over the SW airspace. Areas of sub-VFR are possible tonight but coverage should be limited. Outlook... Sun...Sct showers/Tstorms with sub-VFR restrictions possible especially over the west-central airspace. Mon...Breezy. Showers/thunderstorms likely with periods of sub- VFR. FROPA. Tue-Wed...Breezy with a chance of showers NW 1/2. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/RXR AVIATION...Steinbugl

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