Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 231957 AFDCTP Area Forecast Discussion National Weather Service State College PA 357 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/... Clouds continue to thin over western portions of the region this afternoon. Still thin high clouds but some areas in northwest could be mostly sunny most of the afternoon. Clouds still thick over the southeast. Clouds will hold temperatures down a bit in the southeast. Radar and HRRR imply slight chance rain in SE PA. Several models show the chance increasing after dark. Passing light rain is possible across southern third of region early tonight. POPS are in slight to chance range with higher numbers in southeast. Should be areas of patchy fog. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Overnight lows mainly in the 50s with areas of patchy fog. 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/...
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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.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Afternoon release sent. Mostly cloudy in the southeast and mostly sunny in the northwest. VFR is the rule. There is some rain south of the PA/MD border but so far very light and staying to our south. Some of this rain will creep into southern PA this evening and early tonight. We also will likely see patchy fog develop across the region overnight. So overnight MVFR will dominate perhaps areas of IFR. Fog should burn off relatively quickly Wednesday. VFR most of the day. Clouds will increase west to east as another system approaches. It promises the potential for rain and MVFR/IFR conditions overnight Wednesday into Thursday. .OUTLOOK... Wed...Evening rain KJST/KAOO spreading east. Low cigs possible. Thu...Rain/low cigs likely through at least midday. Fri...Showers/MVFR cigs NW. Mainly VFR SE. Sat...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Grumm SHORT TERM...Grumm LONG TERM...RXR/Steinbugl AVIATION...Grumm

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