Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 270946 AFDCTP Area Forecast Discussion National Weather Service State College PA 546 AM EDT Thu Apr 27 2017 .SYNOPSIS...
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A strong subtropical ridge over the western Atlantic will dominate our weather through Monday. A front will weaken as it moves into the ridge late today, triggering thunderstorms. Then ridge will build westward over the weekend. We will be on the warm, moist western side of the ridge most of the weekend. A classic dirty warm up with warm moist air and potential diurnal thunderstorms. Alas, a strong trough should bring cooler drier weather to the region for the second part of next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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GOES-16 3.9-11.2um loop at 09Z showing stratus becoming more extensive over eastern Pa, as boundary layer cools. It looks like most of the region east of the Allegheny divide will begin the day either cloudy or foggy. Model soundings/SREF prob charts suggest patchy low clouds could linger until midday over the eastern half of the state. Eventual clearing and very warm air at 850mb should result in temps rising to near 80F this afternoon. Main forecast issue remains the potential of a few strong to severe tstorms this evening associated with arrival of a weakening cold front. All guidance timing convection into the western counties between 21Z-00Z. Model soundings showing fairly impressive shear, both 0-6km and 0-1km. However, only modest low level moisture return ahead of front and thus marginal CAPE values expected. SPC has placed roughly the western half of Pa in a marginal risk this evening. Given the strong winds aloft and borderline CAPE, expect isolated damaging wind gusts to be the greatest threat, rather than large hail. Not sure how much weight to place on 00Z NAEFS, which is indicating a high probability of STP>1 across the north-central counties as front comes through around 00Z, suggesting a brief tornado can`t be ruled out.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
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Diminishing frontal showers/storms should push through eastern Pa after dark, as CAPE diminishes and bulk of large scale forcing with parent shortwave lifts north of the region. A dry and slightly cooler Friday is expected, as surface ridging builds in behind cold front. 850 hPa temps remain above normal across the Lower Susq Valley, where readings could again push 80F. Model RH profiles support a mostly sunny forecast for most of the area Friday. Some increasing mid level cloudiness appears likely across the northwest counties during the afternoon, as WAA aloft spreads in ahead next shortwave working across the Grt Lks.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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A weak shortwave passing across southern Ontario/Quebec is progged to push a shallow cold front through Pa Saturday. Timing of this front will favor diurnally-driven convection across the southern counties, where pre-frontal heating could potentially push temps into the mid 80s based on model 850mb temps near 15C. A cold air damming scenario expected Sunday, as dying frontal boundary slips south of the border and sfc high over New England directs a cool southeast flow into central/eastern Pa. Have nudged max temps several degrees below Nationalblend guidance Sunday. Much warmer/unstable airmass west of the mountains could lead to PM tstorms across western Pa, potentially affecting our western counties. Max POPS during the extended period remain centered on Monday/May 1st associated with passage of a potent cold front. A severe weather threat may evolve downstream from the OH Valley into the Mid Atlantic late Monday before temperatures decline to near normal behind the cold front for next Tuesday and Wednesday.
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&& .AVIATION /09Z THURSDAY THROUGH MONDAY/... Low clouds/fog will impact the eastern airfields in ZNY sector with MVFR to IFR conditions this morning. Highest confidence in IFR at LNS (persistence) followed by MDT/IPT but went just above standard IFR vis/cig minimums for the 27/06z TAF). The western 1/2 of the airspace should remain VFR with potential for some MVFR cigs to sneak into AOO/UNV based on latest satellite trends. Timing of improvement over eastern 1/3 of the airspace will also be tricky but expect VFR to return into the afternoon. Focus will shift to broken line of showers/storms crossing the western airspace this evening before weakening or dissipating over the eastern airspace into tonight. There is a risk for a few strong to locally severe storms but time of arrival suggests convection should be in more of a weakening mode during the evening. 20kt wind gusts from 160-190 degrees will be common over the western 1/3 of the airspace today followed by wind shift to 240-270 tonight into early Friday. Outlook... Fri...No significant weather. Sat-Sun...A few showers possible. Mainly dry with VFR conditions for much of the time. Mon...Breezy with showers and thunderstorms likely with FROPA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...DeVoir/Fitzgerald AVIATION...Steinbugl

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