Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 232330 AFDCTP Area Forecast Discussion National Weather Service State College PA 730 PM EDT Tue May 23 2017 .SYNOPSIS... Weak system passing to our south today producing mainly clouds. A very deep upper low will bring clouds across the region Wednesday with rain developing overnight and into Thursday. This deep low will produce cooler showery weather through Friday. As this low lifts out Friday into Saturday a weak upper-level ridge should provide several relatively nice days to start the Memorial Day weekend. Alas another low may approach the region on Memorial Day. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Showers just creeping over the Mason Dixon line this evening...perhaps slightly north of the latest HRRR solution. BKN-OVC skies cover southern and eastern halves of the commonwealth as wave undercuts the region from the south. Passing light rain is expected across the southern third to half of the mid to late afternoon model runs continue to nudge an area of showers into the central mountains after dark. Amounts will be very light...with highest amounts remaining below one tenth of an inch near the MD border. Expect areas of patchy fog across the southern half of PA as well. Overnight lows will range generally through the 50s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Tomorrow we should be mostly between systems. The clouds and moisture from the wave to our southeast should be pulling away overnight. And the clouds and rain from the deep 500 hPa low will be heading our way from the west-southwest. Most areas should have a pretty nice day, but once again on the cloudier side of things. Kept POPS in the chance range in southwest before 18 UTC and brought them up higher and into central PA by 00 UTC. Sometime from 2100 UTC Wed to about 0300 UTC it`s going to get wet. But highest probability of rainfall in current guidance will likely be on Thursday. New guidance might change this. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... As upper low drops into the TN Valley Wed night, surface low develops over the Ohio Valley with a warm front extending eastward across the mid atlantic states. Initial question will be timing of onset of precip over CWA. Precip will be working across W PA by early eve and will spread eastward as flow turns from the SE around to the S, overspreading all of central PA by the overnight hours. System slides through Thu into Thu night, with a widespread rainfall around 0.75 inch. On Friday, cool cyclonic flow on backside of departing cyclone will maintain risk for showers. A lower-amplitude mid level flow pattern will develop into the weekend with some ridging likely at 500mb. Uncertainty regarding location and timing of shortwave impulses rounding the ridge and effect of prior upstream convection leaves plenty of question marks for Saturday - but there is more agreement in area of max POPs over S OH/into WV and SW PA in the afternoon. NBM/ECE blend yielded the highest POPs for Sunday across Central PA associated with cold front moving south/eastward across the Great Lakes/Appalachians. A severe risk may accompany the cold front but still to early for details. The large scale pattern evolves into a broadly cyclonic regime into early next week around an upper low between the Great Lakes and Hudson Bay. This should keep the pattern unsettled with continued threat for showers/Tstorms through Tuesday. && .AVIATION /23Z TUESDAY THROUGH SUNDAY/... Most of the flying area is under a blanket of high clouds. Far SERN Pa is closer to an area of rain that is blossoming up over the Mid Atlantic States and will continue to spread NE overnight. Expect the mainly light rain to move into about the southern half of the forecast area during the mid to late evening with MVFR/IFR conditions developing. Northern areas will see just spotty light showers and sub VFR conditions are not expected. Conditions will improve slowly Wednesday morning with most areas improving to VFR by mid day. Clouds will increase west to east as another system approaches with rain and reduced conditions overnight Wednesday into Thursday. .OUTLOOK... Thu...Rain/low cigs likely through at least midday. Fri...Showers/MVFR cigs NW. Mainly VFR SE. Sat...No sig wx expected. Sun...Reduced conditions with scattered showers. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Grumm/DeVoir SHORT TERM...Grumm LONG TERM...RXR/Steinbugl AVIATION...Grumm/La Corte is the U.S. government's official web portal to all federal, state and local government web resources and services.