Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 260943 AFDCTP Area Forecast Discussion National Weather Service State College PA 543 AM EDT Wed Jul 26 2017 .SYNOPSIS...
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An expansive ridge of high pressure extending across the central and northern Appalachians will bring us a pleasantly warm day with comfortable humidity. Mid level clouds will increase from the west tonight into Thursday. A cold front will push gradually southeast across the district late Thursday night through Friday morning with numerous showers and isolated to scattered thunderstorms. Another wave or two low pressure will likely form along this front as it sags to the southern border of the state, bringing some additional periods of rain Friday afternoon into Saturday morning, mainly across the southern portion of Pennsylvania. Another refreshingly drier and cooler airmass will overspread the commonwealth this coming weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1026mb sfc high centered over northern VT has a ridge extending down along the Appalachians into PA early this morning. A weak inverted trough and marine layer to its east was producing some fairly thick low clouds and evening some light showers/drizzle invof KRDG and KLNS. Mentioned isolated to sctd SHRA in that part of the CWA this morning, but even these low chcs decrease this afternoon as the mean low to mid flow becomes south to southwest. Elsewhere across central and western PA, today is shaping up to be quite nice with abundant sunshine mixing with increasing mid and high clouds late. Temps will be near normal across the northern and wrn mtns, and a few to svrl def F below normal elsewhere. The 20-25F air/stream delta T has resulted in patchy dense valley fog (mainly across nrn PA) where temps early today were in the upper 40s to low 50s. Elsewhere, mins early today varied from the upper 50s to lower 60s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
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Increasing dual to multi-layer clouds advect east/SE into the state later tonight through Thursday morning with little more than some scattered and brief showers drifting over the area. Deep layer warm advection and a return to a notable higher PWAT airmass will occur in advance of a cold front and another upper deepening, but rather compact upper trough headed our way from the Great Lakes region. Anomalous PWATs on a SW to NE axis will top out between 1.5-1.75 inches over the state Thursday afternoon and night before likely settling just south of the state on Friday.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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The last cycle or two of model run shows a highly anomalous northeasterly flow in the sfc-850 mb layer developing Friday into Saturday as a strengthening wave (or two) of low pressure at the sfc develops/moves east from the Ohio River Valley and passes near the Mason/Dixon. Thick clouds and a strengthening north to nwrly ageostropic llvl flow will combine with moderately strong llvl cold advection to bring a quite chilly day for late July. Highs Friday could struggle to climb above the mid 60s across the higher terrain of the north and west, while highs in the Central valleys come out to be in the low-mid 70s. The strength of the expected sfc low shown by multiple models and EFSs and the approximate -3 sigma 925-850 mb wind will be quite a rarity in the Mid Atlantic region for Mid Summer. A significant severe weather outbreak will likely occur near and just to the south of the aforementioned sfc low track. Q widespread light to moderate, chilly rain event (with locally heavy amounts and elevated instability/thunder across the south) is expected for Friday afternoon into Saturday morning, followed by a chilly airmass for later Saturday into Sunday as the northerly llvl wind anomaly strengthens to -3 to -4 sigma in the wake of the deepening low just off the southern New England coast. Conditions eventually dry out later Saturday and Saturday night with a gusty north to northwest wind as high pressure builds in. Sunday and Monday appear mainly dry at this time as the sharp mid level thermal trough slides off the Mid Atlantic Seaboard.
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&& .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/... As high pressure builds in from the west, shallow marine layer under lowering inversion is developing a lower cloud deck over the northern tier (KBFD), which will thicken through 12z. In addition, a more widespread lower stratus deck over eastern PA is edging back into the Susq Valley from the east. This lower stratus deck will bring a period of MVFR to IFR conditions into mid morning. If that`s not enough, in central areas radiational cooling, combined with light winds, is bringing formation of valley fog, with it`s own associated restrictions in visibility and low ceilings through ~13z. The clouds and fog will erode by mid/late morning, with VFR conditions expected by mid day across entire region. Tonight, mainly mid/high clouds thicken ahead of an approaching system due on Thursday. But low ceilings could again sneak into eastern terminals from eastern PA toward sunrise. Numerous showers and scattered thunderstorms return for Thursday afternoon and night with the approach of another cold front. .OUTLOOK... Thu...VFR, but with restrictions developing in SHRA/TSRA. Fri...Scattered SHRA north with more numerous and heavier SHRA/TSRA across the south. Sat-Sun...No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...DeVoir/Lambert AVIATION...RXR

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