Area Forecast Discussion
Issued by NWS State College, PA

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641 FXUS61 KCTP 291616 AFDCTP Area Forecast Discussion National Weather Service State College PA 1216 PM EDT Mon May 29 2017 .SYNOPSIS...
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A trough of low pressure will stall out over central and eastern PA today, before retreating back into the Central Mtns tonight. Another cold front will push toward the region Tuesday and combine with the lingering boundary to produce numerous showers and scattered afternoon thunderstorms, some of which could contain gusty winds and hail. Low pressure at the surface and aloft will stay centered near James Bay Canada through the rest of the week. This weather feature will supply a period of slightly cooler than normal temperatures, and push a few additional weak cold fronts through the commonwealth accompanied by scattered showers and perhaps some isolated afternoon and early evening thunderstorms.
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&& .NEAR TERM /UNTIL 8 PM THIS EVENING/...
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Weak surface front stalling over the Susquehanna Valley this midday hour with plenty of clearing and a light to mdt westerly wind across the Central and Western Mtns of PA. to the east of the boundary, cool and cloudy airmass will prevail with temps only climbing slowly into the 60s. Max temps elsewhere will be mainly in the 70s, with mid-upper 70s likely in the central and southern valleys to the SE of a KAOO to KUNV line where the llvl westerly downslope flow and heating will be maximized. Differential heating along the western edge of the cloud boundary across the Susq Valley will lead to a ribbon of enhanced cape and moisture convergence which will help to produce scattered showers and isolated TSRA per the latest 14Z HRRR. The convection should drift to the east and greatly weaken within 20-30 miles east of the stalled out llvl boundary.
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&& .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM TUESDAY/...
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Brief ridging will allow the skies to clear over the western two-thirds of the CWA this evening, and residual moisture may lead to areas of fog, especially in the central valleys. The low level moisture and low stratus deck AOB 1000 ft AGL will push gradually westward across the Central Mtns and West Br Susq Valley and stay intact through early Tuesday. Mins tonight will dip into the 50s for most, as the dewpoints will be the bottom limit. A separate, weak sfc trough will be pushed into the area from the northwest tonight. 8H temps fall a bit over the NW. Heights fall just a little, too, so some precip is possible before sunrise Tuesday over the northwestern third of the area, but it should be light. The trough begins to catch the stalled trough over the eastern counties. The southerly or southeasterly wind will yield good convergence and will crank up some showers and thunderstorms. Have painted high POPs for the area, but the amount/severity of destabilization is in question with the clouds in the NE early in the day. NAM cranks out 1500joules of CAPE and LI drops to -2 or so in the mid-day and aftn on Tues. SPC marginal Risk of svr wx for Day 2 (Tues) is painted across our eastern half, focused on the peak heating time. Will continue to mention this in the HWO.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... The long term period will be dominated by a large upper level low the will be slowly moving through the upper Great Lakes and southern Canada. As that quasi stationary low slowly moves to the northeast, it will bring surges of cool moist air across the region. Several successive shortwave will move through mid to late week which will bring the possibility of scattered showers with preference for the majority of the QPF (albeit quite light at that) to be across the typical west-nwrly flow upslope prone areas of the Laurel highlands and NW mtns. The chance for any thunder will be very minimal Wed and Thursday. Generally dry NW flow occurs late in the week into next weekend as a 1020 sfc high over the upper midwest Friday evening builds SE twd the region. Pops Thur night through Fri night will be 30 percent or less. Late in the week the models begin to diverge on the location and timing of the upper level low so there is less confidence on precipitation late in the week. However depending where the boundary sets up there could be periods of showers Friday through Saturday, though currently should be mainly along the Southern border. && .AVIATION /16Z MONDAY THROUGH FRIDAY/...
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Widespread sub VFR cigs will be difficult to clear east of a line from KIPT to KSEG and KMDT this afternoon, and if so, it will be only for a brief few-svrl hour period. Llvl easterly flow of 5-10 kts will likely persist over, and to the east of the susq valley with MVFR to IFR cigs and VFR to MVFR vsbys in light fog/hz. Sct-bkn VFR strato cu and cu will occur across the western two thirds of the state thanks to a drying, light to moderate westerly llvl wind. Depending on how much clearing occurs/remains this evening, widespread fog formation is possible region-wide tonight. Later on, expect the stalled out boundary across the Susq Valley to drift westward back to the Allegheny Front (KAOO, KUNV and KIPT) by...or shortly after 04Z Tuesday. .OUTLOOK... Tue...morning IFR Stratus likely across much of central and SE PA, then breaks in/lifting of the cloud deck leading to MVFR to low-end VFR conditions with showers becoming more numerous during the late morning and afternoon hours. Also, scattered afternoon TSRA with brief, localized greater reductions. Wed...Chance of showers. Thu...No sig wx expected. Fri...Chance of showers and thunderstorms.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert/Dangelo LONG TERM...Lambert/Ceru/Martin AVIATION...Lambert/Gartner

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