Area Forecast Discussion
Issued by NWS State College, PA

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214 FXUS61 KCTP 240034 AFDCTP Area Forecast Discussion National Weather Service State College PA 834 PM EDT Sun Apr 23 2017 .SYNOPSIS... A storm system over the southeastern states will begin to make slow progress northward along the coast over the next several days. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... High clouds have begun to fill the sky as moisture swirling around a potent upper low over TN surges northward. They are thickest over the south, thinnest over the north. 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 mid/high clouds will help to curb the temp fall across the south. Mins will be mainly between 40-45 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. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... 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. && .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. However as we get into Tuesday around 12Z the ensembles begin to diverge. The 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 adjusted the orientation and adjusted POPS accordingly. The gradient will be tight on any precipitation amounts. Once this system goes by it will get warm fast. It should feel like summer through the second half of the week. 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. Thursday through at least Saturday should be very warm and humid. We should have several days with high temperatures around 80. Thursday into Friday will see the passage of large upper level trough. Have left broad POPS as this trough will move a corresponding front through. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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High pressure and associated dry air mass over Pennsylvania will ensure widespread VFR conditions and light winds through tonight. Latest LAMP and downscaled NAM suggest there could be some patchy fog in vicinity of MDT/LNS early Monday morning. However, given the expected amount of cirrus, feel signficant fog formation is unlikely. Low pressure lifting up the east coast will spread lowering clouds and spotty light rain into southern Pa Monday. Initially, dry air in the low levels should keep conditions VFR. However, model soundings and SREF prob charts suggest MVFR conditions will become likely by Monday evening across southern Pa, with IFR even possible at AOO/JST. Outlook... Tue...Rain/low CIGs likely. Wed...AM rain/low CIGs possible. Thu...AM fog possible. PM tsra impacts possible. Fri...PM tsra impacts possible.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...La Corte/Lambert SHORT TERM...Lambert LONG TERM...Dangelo/Ceru AVIATION...Fitzgerald

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