Area Forecast Discussion
Issued by NWS State College, PA

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460 FXUS61 KCTP 200905 AFDCTP Area Forecast Discussion National Weather Service State College PA 505 AM EDT Sun May 20 2018 .SYNOPSIS...
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Widely scattered and generally brief showers will accompany the passage of a weak cold front this morning. Drier air will finally work into the region during the late morning and afternoon hours today as the front pushes south of the state. During the day Monday, this same old frontal boundary will lift back northward as a warm front, bringing increasing chances for late day showers and even a thunderstorm across mainly the southwest third of the states. Numerous showers and scattered thunderstorms will occur Monday night and Tuesday as a warm front lifts gradually to the northeast across the Commonwealth.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Regional Dual Pol loop at 0830Z shows widely scattered, mainly light and brief showers drifting east across the central and western potions of the CWA, along and just ahead of a cold front. The front was located on a line from CYYZ to KERI and KCMH. This front is projected by the latest HRRR to slide through the Central Ridge and Valley region of the state and the Laurel Highlands about 14Z today before pushing across the Lower Susquehanna Valley in the 17-18Z timeframe. Sfc based cape ramps up to 1000-1500 J/KG during the mid to late afternoon hours across our far SE zones, so a thunderstorm was mentioned there along with the overall chc for a few brief showers. Latest HRRR/SPC HREF temps today are in good agreement with our current gridded forecast values, which vary from the upper 60s across the northern tier counties of PA, to around 80F in the Southeast. Downslope northwest flow of 10 to 12 kts with some gusts into the mid teens range will help to erode the moisture that`s been with us, and stuck in the deeper valleys since late Friday. Look for increasing sunshine in the wake of the CFROPA during the midday and afternoon hours today across the NW half of the state, while a fair amounts, several kft or more in thickness will be found across the Lower Susquehanna Valley.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
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High pressure over the Upper Midwest/Northern Great Lakes will build SE and moves across Pennsylvania late tonight through the midday hours Monday with fair/dry weather, lower humidity and light wind helping to yield cool temps. Lows tonight will vary from the upper 40s across the Northern Tier of PA to the lower 60s in the Southern Valleys.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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After being suppressed to our south early next week, the chances for showers will increase once again Monday as moisture on the northern periphery of the subtropical ridge creeps back into the region as an old frontal boundary lifts to the NE as a warm front. Diurnal nature of convection will bring mention mainly over the SW third of CWA for mainly afternoon showers /thunderstorms. Interestingly, GFS indicating a ribbon of drier air sliding across the north (ahead of moisture return) just off the surface that should mix down midday over the northeast and could drop dewpoints into the lower 40s at KIPT for several hours. Showery forecast sticks around Monday night into Tuesday before drier air makes a push in from the NW starting Wednesday. Tuesday looks potentially cooler than current guidance with clouds/showers around, esp over the southern half of CWA. So undercut MOS by a couple degrees. From there it looks like the period form Wednesday through Friday will feature some rare (of late) rain-free conditions, before the chance for a pop-up shower or storm becomes returns for Sat. Temps look to climb into the 70s each day, with Saturday the warmest as high range from the mid 70s to the lower 80s. The coolest morning will be Friday with valleys of the northern mountains dipping into the mid 40s.
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&& .AVIATION /09Z SUNDAY THROUGH THURSDAY/... Cold front over Lake Erie at 06Z will press southeast into the central airspace by 12Z then slow down before exiting the airspace by 00Z Monday. Expect a transition period and general improving trend over the next 12 hours from widespread IFR to variable/mixed flight categories later Sunday morning to MVFR/VFR by Sunday afternoon. Widely scattered showers are possible ahead of the front along with an isolated thunderstorm this afternoon over the southeast airfields. Did not include specific mention of showers in the TAFs due to limited coverage/confidence in terminal impacts. A downsloping wind shift to the west northwest (270-310 degrees) will help with the anticipated improving trend. Outlook... Mon-Wed...Variable conditions with showers and thunderstorms at times. Thu...AM Fog. Otherwise VFR/no sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/RXR AVIATION...Steinbugl

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