Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 280357 AFDCTP Area Forecast Discussion National Weather Service State College PA 1157 PM EDT Sat May 27 2017 .SYNOPSIS... Low pressure will slide by just to the south of the Mason/Dixon line overnight, while weak high pressure just to our north supplies dry weather and light wind across practically all of Central PA. A warm front will approach from the south as a cold front approaches from the west Sunday, with the cold front eventually passing through Monday morning. Low pressure will stall over northern Ontario mid-week and create a slightly cooler than normal and unsettled stretch of weather. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... GOES R fog product shows variably cloudy skies with the most clouds generally hugging the PA-MD border. Weak ridging at the surface and aloft will build across most of the state overnight bringing dry and milder temps in most areas than what we have seen on recent nights. Min temps across will range from around 50 over the north to the mid 50s south. Areas of fog will be possible late tonight through the mid morning hours Sunday, especially on the east facing slopes of the Alleghenies where a light SE upslope flow will be developing, and could even support some patchy drizzle after midnight. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... The mean sfc-850 mb flow becomes more southeasterly, then southerly in advance of the storm and sfc cold front approaching from the west. The chance for storms increases on Sunday afternoon. The destabilization will be easiest in the east where less low clouds are expected, but the deeper moisture is off to the west and the dynamics are even farther to the west. PWAT goes above 1.5 inches in the west by the end of the day Sunday. Will ramp POPs up in the west through the aftn, leaving the east in chc or less POPs. Due to the expected extent of low clouds to start the day...followed by thickening mid and high clouds/and increasing chc for showers/sctd tsra, we leaned away from the Nat`l Blend and more toward the cooler NAM for high temps - in the u60s to low 70s. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... A quick transition to increasing deep layer moisture and higher PWAT air of 1-1.25 inches will occur late Sunday. A large-scale trough and increasing upper level divergence (associated with a lead upper shortwave in the west/SW flow) will lead to a fairly large area of moderately strong uvvel and a widespread moderate rainfall along and ahead of a cold front. GEFS Probs for GE 0.50 inch of rain/24 hours ranges from 50-80 percent across the wrn mtns of generally less than 50 percent across the eastern half of the state. This translates into very high POPs for measurable rain (90 percent or more) across the western half of the CWA, to between 70 and 90 percent across the south-central mtns and Susq Valley. 12Z EC and 12z GEFS are in very good agreement on the timing/location of the north/south sfc cold front during the afternoon hours Monday across the eastern half of the state with weak deep- layer ridging and drying for Monday afternoon and night. Dry conditions expected Tuesday morning before significant cooling aloft accompanies a pair of short waves late Tuesday and later Wednesday. POPs during this midweek period will be painted as chc - translating to 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 Tuesday through 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. After our bout of coolish weather with temps several Deg F below normal Sunday and Monday, GEFS mean temps rebound back to near or slightly above normal (even under slightly cooling 850 mb temps) for Tuesday through at least Thursday. ECENS mean temps are several deg warmer than the GEFS and Nat`l Blend of Models temps. leaned closer to the cooler solutions based on the few-svrl deg C of cooling aloft with near to slightly below 850 mb temps. && .AVIATION /04Z SUNDAY THROUGH THURSDAY/...
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Weak ridge of high pressure will build across the region tonight, resulting in a calm wind and conditions favorable for fog formation. GOES 10.3-3.9um imagery already showing developing low clouds/fog across the southern tier of Pa at 04Z and dewpoint depressions suggest IFR/LIFR conditions could begin as early as 05Z at AOO, while much of the remainder of central Pa is likely to experience fog formation between 06Z-09Z. At this point, would categorize IFR/LIFR conditions as likely at JST/AOO/LNS/UNV/MDT overnight and around 30 pct at IPT. Early low clouds/fog will begin to lift after 12Z, with VFR conditions expected in most locations by afternoon. However, there is at least some potential of a moist sse flow into the mountains creating a MVFR stratus deck along the east slopes of the Appalachians from BFD south through UNV,AOO and JST. The other area of concern will be isold tsra impacts across the western airfields associated with a warm front pushing into the region. .OUTLOOK... Mon...AM showers/low cigs possible. Tue...No sig wx expected. Wed...Slight chance of showers/reduced cigs. Thu...No sig wx expected.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...Lambert LONG TERM...Lambert/Ceru AVIATION...Fitzgerald is the U.S. government's official web portal to all federal, state and local government web resources and services.