Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 251043 AFDCTP Area Forecast Discussion National Weather Service State College PA 643 AM EDT Tue Jul 25 2017 .SYNOPSIS... An upper trough will slide to the Northeast U.S. coast today. In its wake, high pressure will build southeast from the Great Lakes and become centered over the Middle Atlantic Region on Wednesday. A cold front will likely push southeast across the region late thursday night through Friday morning. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Low-Mid level thermal trough located right over the region early today and was supporting an extensive area of bkn-ovc stratocu with bases blo 2000ft AGL across the Alleghenies of northern and western PA. The clouds will persist into the late morning...before slowly breaking up and lifting this afternoon. Most of the cloud cover should be limited to the western ridges of the Laurels and the northern tier counties during the mid to late afternoon hours as high pressure gradually builds in, and the coolest air aloft shifts east of the CWA with llvl downsloping helping to dry out the boundary layer SE of the I-99/RT 220 corridor. Overall, expect a much more pleasant airmass with comfortable humidity acrs the region today with little to no chance of rain for a change. Did mention very low chcs for a few brief/light showers across the north and east today. Over the north, some limited moisture from the warm water of Lake Erie will be transported SE and lifted across the higher terrain bringing isolate light showers, while across the east, an inverted sfc trough/marine layer boundary will be located mainly to the east of the Susq valley and bring with it a slight enhancement to llvl theta-e convergence and the slight chc for an afternoon shower. Clouds will continue to thin out and retreat north late today/this evening. Max temps this afternoon will vary from the upper 60s across the northern mtns to around 80F across the SE part of the CWA. These readings will be 5-8 deg F below normal with the greatest departures occurring across the NW mtns. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... High pressure will build over the region late tonight and Wednesday, bringing clear to partly cloudy skies and dry/cool conditions tonight, followed by a quite spectacular mid-summer day for most places Wednesday - with abundant sunshine a light southeast to south breeze, comfortable humidity and slightly below normal temps. The lone concern will be associated with a marine layer and easterly flow near and to the east of the Susq Valley that could bring some clouds and a slight chance of a shower into the eastern zones Wednesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Low to mid level warm advection increases Wednesday night and Thursday with mainly and increase in non-precipitating alto cu clouds. There will be an increasing chance for showers and scattered tstorms mainly Thursday afternoon and night as the cfront and attendant above normal pwat axis drifts SE across the commonwealth. A weak wave of low pressure may develop along the front and move across southern PA, enhancing precip rates and possibly causing the convection to linger over southern PA (esp across the Lower Susq Valley) on Friday. Conditions dry out for Saturday as high pressure builds in. A wave on the front that moved south of PA may bring showers up around the Mason-Dixon line Sunday. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Axis of upper trough overhead this morning will lift off to the east as the day progresses. At the surface, high pressure already building in from the west will take control through midweek. Dealing with post-frontal NW flow driven cloud cover this morning as building surface high squeezes moisture under subsidence inversion, creating IFR conditions over the west/north (and even a few light showers around BFD) and MVFR into the central mtns. These will mix out to VFR by mid morning in central areas and late morning over the west/north. Lower Susq remains VFR, though there are some lower cigs over eastern PA that are not expected to expand westward. Winds will be from the NW around 10mph early, shifting to the north at 5-10mph midday. Could see a return of restrictions with a stratocu deck over the northern mountains tonight (and maybe a lower deck edging into the Susq Valley from the east), but elsewhere only expecting some valley fog to develop (even though dewpoints bottom out tonight, there remains a good bit of ground mousture around from recent rains). This fog will likely impact several terminals toward sunrise Wed. Otherwise, Wed should bring good flying weather with VFR conditions and light winds turning around to the east then south as high pressure slides off to the east. Scattered thunderstorms return for Thursday. .OUTLOOK... Wed...AM cig restrictions north. AM Patchy valley fog areawide. Otherwise no sig wx. Thu...Scattered afternoon/evening TSRA/SHRA. Fri...Slgt chc of morning shra...otherwise VFR. Sat...No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Watson/Lambert AVIATION...RXR

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