Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 220350 AFDCTP Area Forecast Discussion National Weather Service State College PA 1150 PM EDT Tue May 21 2019 .SYNOPSIS... A ridge of high pressure will build east across the Commonwealth tonight and slide off the Mid Atlantic Coast by Wednesday evening. Fair weather will prevail through Wednesday afternoon, but much higher humidity will surge into the state from the Ohio Valley Wednesday night and Thursday, bringing an increasing chance for showers and Thunderstorms. Pennsylvania will be on the northern periphery of a building subtropical ridge late this week and over the upcoming weekend. This will mean occasional bouts of mainly afternoon and evening showers and thunderstorms. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Fair weather and light wind expected overnight, as surface ridge builds over the region. Satellite loop shows some mid and high level cloudiness poised to overspread Pa from the west overnight. Therefore, believe earlier concern for patchy frost over the NW Mtns is diminishing. Min temps at sunrise Wed should generally vary from the upper 30s in the perennial cold spots of the north, to around 50F in the larger metro areas of the southeast. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... After a fair tranquil and cool start with high pressure overhead, southeasterly llvl flow will increase during the day as the high pressure ridge drifts off the NJ Coast. Several layers of clouds will also form/advect east into region as the nose of much higher PWAT air (30-35mm or +2-3 sigma) spreads into Western PA late in the day. A small chc for showers exists across the Alleghenies of west-central PA from mid afternoon into early evening, as low level jet pushes into the western part of the state. NBM/Superblend numbers support fairly uniform max temperatures across the forecast area, ranging from the upper 60s to low 70s. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... NAEFS indicates Pennsylvania will be on the northern periphery of a building subtropical ridge later this week into the weekend. The most significant weather during the extended looks like it will be on Thursday when the ingredients for a severe storm outbreak look most likely. Models show an advancing warm front late Wednesday night into Thursday morning. The deterministic models all show some remnant convection sliding through PA associated with the warm front and at least one weak shortwave aloft that will be racing over the top of the eastern ridge. Progged stability indices indicate the warm front will move through the CWA Thursday morning, with moderate instability developing over the region during the late morning into the afternoon hours. A robust shortwave is made to approach during the second half of the day pushing a potent mid level speed max down and through the area during the afternoon hours. Deep layer flow will be out of the WNW with the models developing impressive helicity on the order of 2-3(m^2/sec^2). The most likely scenario will be for storms to develop over the lower lakes and spread ESE across the region during the afternoon in short lines and bowing segments along with the possibility of isolated supercells. In the wake of the Thursday system a slightly cooler and drier day is in store for Friday. By Saturday the humidity will begin to return along with a chance of mainly diurnal showers/storms. as a weak shortwave once again races over the top of the eastern ridge. We look to get a break on Sunday as the 12Z models show a mainly dry day, but by the Monday-Tuesday timeframe more showers become possible as we stay in fast flow aloft near the top of the subtropical ridge. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/... A ridge of high pressure will build east across the Commonwealth today and slide off the Mid Atlantic Coast Wednesday evening. VFR expected over all routes today and tonight. Winds will light and variable overnight. VFR conds prevail overnight and Wednesday, with winds shifting to the southeast and increasing later Wednesday morning afternoon. .Outlook... Tue-Wed...Mainly VFR. Thu...VFR into the afternoon, then strong thunderstorms possible mid afternoon into Thu night. Fri...Ceiling restrictions poss NW early, then mainly VFR. Sat...scattered restrictions possible from potential showers and thunderstorms. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald/Lambert LONG TERM...La Corte AVIATION...DeVoir/Gartner is the U.S. government's official web portal to all federal, state and local government web resources and services.