Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 221951 AFDCTP Area Forecast Discussion National Weather Service State College PA 351 PM EDT Sat Apr 22 2017 .SYNOPSIS... A frontal boundary will remain stalled out just to the south of the state as a few weak waves of low pressure ripple northeast along it. An upper level cut off low will form over the Tennessee Valley late this weekend, and could end up bringing a storm slowly up the East Coast in the first part of the upcoming week. && .NEAR TERM /UNTIL 8 PM THIS EVENING/... Radar mosaic shows several bands of light-mdt rain showers streaming to the NE, and covering approximately the SE third of our forecast area as of 1730Z. The showers were being generated by a broad area of mid-level FGEN forcing and uvvel beneath the thermally direct/RE region of a 95-105 KT upper jet core draped from the Ohio River Valley to central New York at midday. High res models agree very well with what we`re seeing on regional radar loops late this morning, that being that the NW edge of the showers will be gradually shifting to the SE through the midday and afternoon hours, and becoming confined to the region near or to the SE of I-81 after 18Z as another mid and upper level disturbance (and weak wave of 850mb low pressure) arrives from the Middle Ohio River Valley and Central Appalachians as it rides NE along the 850 mb front that`s stretched out along the I-81 corridor. Expect additional rainfall (from the current departing area of showers, and the mid to late afternoon arrival of the second area) to average between 0.10 and 0.25 of an inch across the SE third of the CWA for the rest of the day, with nothing more than a a few sprinkles near and just to the north of a line from KJST and KAOO to KSEG from the gradually lifting and SE drifting mid level cloud deck. Breaks of sunshine will occur through the dual stratocu and altocu deck across the NW half of the State. Temps will hold between 45-50F in the higher elevations. We may reach the upper 50s in some locations throughout the Central Valleys and Mid Susq valley - with the best chance for that probably in the EC zones. the more persistently rain-cooled air across the SE will keep temps pretty steady between 52-55F. && .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SUNDAY/... Rain is expected to press to the south of the Mason-Dixon line very early this evening as deepening dry air advects in from the north-northwest ahead of a ridge of high pressure. It should remain dry - even in the south - for the rest of the weekend with POPs less than 15 percent across the southern tier counties. Temps will get pretty chilly Sunday morning, especially in the mountains. Much of the valley areas in central and Southern PA will see the mercury fall into the U30s and L40s. However, it will probably dip into the mid-upper 20s in the perennial cold spots near KBFD - and between 30-35F over the rest of the NW third to half of the CWA. Wind will be calm or light/northerly. Much of the area will clear out. The average date of the last spring freeze has passed for the SE third of the area, and there could be some frost in the ridge and valley region (between UNV and MDT). Will hold off on any mentions of frost in the wx grids/zones for now. Subsidence will lead to plentiful sunshine on Sunday. Temps should rebound nicely with almost all of the area back into upper 50s and lower 60s. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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The period of Sunday night to Wednesday will be dominated by the flow around a slow moving cut-off low which eventually will pass to our south and east. This system will bring clouds and light rain to the parts of our region for several days. The models are in fair agreement on timing and position of this low. Bands of precipitation should begin to streak through the region, mainly the east Tuesday morning. Timing and position of the low will change whether or not different portions of central Pennsylvania get precipitation. Have increased POPS for eastern PA. The gradient will be tight on any precipitation amounts. Once this system goes by large scale retrogression will put our region on the western edge of a relatively strong 500 hPa ridge and it will get warm fast. It should feel like summer by next Thursday. The potential for rain will be higher in southeastern PA and much lower in northwestern PA. Rainfall will likely be very light and the best chance for measurable rainfall will be in southeastern PA. Enjoy the mostly cloudy and relatively cool weather while it lasts. As the 500 hPa low fills and the attendant moves to our northeast the chance of rain should fall off Wednesday into Wednesday evening. Our 850 hPa temperatures will rise rapidly Wednesday and it should be noticeably warmer Wednesday relative to Monday and Tuesday. Thursday into Saturday the 850 hPa temperatures will be well above normal, mainly in the 14 to 16C range and we will be on the western edge of a rather impressive early season subtropical ridge. The GEFS and GEFSBC show a closed 5880 m ridge along the VA/NC/SC coast with +2 sigma height anomalies by Fri-Sat. Thursday through at least Saturday should be very warm and humid. We should have several days with high temperatures well into the 80s. Any precipitation after Wednesday will likely be in a more summer-like atmosphere so have kept thunder in all forecasts beyond Wednesday. The ridge will likely continue retrograding. If the NEAFSBC and GEFSBC are correct we could be looking at our first enduring period of warm weather from this coming thursday into the following week.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Radar loop at 16Z showing several bands of showers covering the SE third of the state, and shifting gradually to the east. Expect dry conditions there for a few hours early this afternoon, before another batch of light to moderate showers impacts the KMDT and KLNS areas between 18-22Z. Cooler and moist llvl air in the wake of the slow moving cold frontal boundary across Central PA will bring some MVFR strato cu clouds early this afternoon across the NW mtns and Laurel Highlands (Including KJST and KBFD) as that air is lifted orographically. There should be enough dry air and weak downsloping in the low levels to preclude significant CIG reductions across the SE half of the state. However, the periods of showers near and to the SE of Interstate 81 will be accompanied by brief 4-5SM MVFR vsbys at KMDT and KLNS during the afternoon hours. Generally VFR Cigs and Vsbys will occur elsewhere at airfields across Central Mtns this afternoon including KAOO, KUNV and KIPT. Any showers should exit southeast Pa by early this evening. After that, a drier northerly flow should ensure widespread VFR conditions tonight. Outlook... Sun-Mon...No sig wx expected. Tue...Rain/low CIGs possible. Wed...AM Rain/low CIGs possible, mainly eastern Pa. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Dangelo/Ceru AVIATION...Lambert is the U.S. government's official web portal to all federal, state and local government web resources and services.