Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 231852 AFDCTP Area Forecast Discussion National Weather Service State College PA 252 PM EDT Sun Apr 23 2017 .SYNOPSIS...
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A frontal boundary will remain stalled to the south of the state into Monday as an elongated east/west ridge of high pressure drifts across the commonwealth. An upper level cut off low drifting across the Southern Appalachians will help to slowly strengthen an area of surface low pressure along the southeast coast by Monday evening. This surface low will likely turn north and move slowly up the East Coast Tuesday and Wednesday bringing residents across the eastern half of Pennsylvania showers, or even a few periods of steadier rain Tuesday into Wednesday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Abundant Sunshine and a light and variable to easterly wind will prevail through the rest of the daylight hours with just an increase in in cirrus/cirrostratus occurring over the southern half of the state. Temps are nearing their forecast maxes in the low-mid 60s in most places, while readings were still holding in the mid to upper 50s across the Laurel Highlands, where the thickest high cloud cover has occurred. It will remain dry tonight with a ridge of high pressure holding on across the northern tier counties of PA, while the northern extent of deepening, moist easterly flow off the Atlantic advects north to near the Mason/Dixon line well after midnight. Variable amounts and thickness of high, then mid clouds will help to curb the temp fall across the south (in the otherwise cool and bone dry airmass). Mins will be mainly between 40-45F throughout the Central and Southern counties of the state. Mainly clear skies should continue through most, or all of the night aver the northern mountains with temps dipping into the 30s and some patchy frost forming.
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&& .SHORT TERM /MONDAY/...
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The aforementioned upper low will deepen and cut off over the Southeastern states Monday before taking a left hand turn and drifting north along the Mid Atlantic Coast later Monday through Wednesday. The main core of the anomalously strong, moist southeasterly winds (approx -3 sigma U-component of the 850 mb wind), will move from VA and NC Late Monday, to Southern and Eastern PA by Tuesday afternoon. This translates into gradually lower and thickening clouds Monday and Monday night with some light rain or showers expected to spread in from the south during the mid to late afternoon hours across the far south, before reaching the Interstate 80 corridor around or shortly after midnight Monday night. Rainfall does not look heavy on Monday, as the best moisture/easterly wind anomalies pointed to the south of the state and the sfc low will still be down near Myrtle Beach. Similarly mild high temps are expected across the northern PA TAF sites, while temps cooler than Sunday by some 8-10 deg F are forecast across the south. Mid to upper 50 deg highs for the south Monday could be a few to several deg F on the high side.
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&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... The period of Monday Night to Tuesday Night 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. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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Nice, VFR flying conditions will prevail through the rest of the daylight hours today with just a gradually increase in high clouds across southern PA. Winds will be from the NE to East at 5-9 kts in many locations, though some gusts into the teens will occur across the Laurels INVOF KJST. Patchy light rain could push back into the far, southern tier counties of PA early Monday morning, as a complex storm system forms across the southeast states and drifts slowly north up the eastern seaboard. Some rain could get into central areas later Monday afternoon or evening, and perhaps into northern PA Monday Night. Potential for a wet day on Tuesday, as a complex low lifts northeast along the coast. Improving conditions for Wed as the upper low and the moderately strong llvl easterly flow heads northeast toward the New England states. Showers and thunderstorms spreading eastward, along and ahead of a cold front on Thursday. Outlook... Mon...Patchy rain spreading slowly northward. Tue...Rain/low CIGs likely. Wed...Improving conditions. Thu...A chance of showers and Thunderstorms.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Dangelo/Ceru AVIATION...Lambert

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