Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 282327 AFDCTP Area Forecast Discussion National Weather Service State College PA 727 PM EDT Sun May 28 2017 .SYNOPSIS... A warm front over western Pennsylvania will drift slowly northeast across the state tonight and early Monday. A cold front will push east from the Ohio Valley and cross the state during the day Monday. Low pressure will become stalled over northern Ontario during mid-week and will lead to a period of slightly cooler than normal temperatures and occasionally unsettled weather during the upcoming week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Meso anal shows a stark contrast between the warm-humid air streaming into western PA and the cold dome of cool-air damming stuck over central PA. Convection is and has been firing where the 2 airmasses are clashing giving a real life lesson in mesoscale meteorology. A gust front worked west out of the Laurels and helped fire new storms between PIT and Somerset county. Another gust front worked south through NWRN pa and has helped fire off an even more impressive line of storms that currently extends from NW Clearfield county westward to Franklin and Youngstown. It`s this area of convection that the HRRR consolidates and marches slowly ESE into the Central Mountains later this evening. The threat for severe storms seems to be diminishing in favor of locally heavy rain. We have already had some flooding in and around Somerset, and the iff the HRRR is to be believed, a large area of 1-2 inches of rain will be the end result over a large chuck of our central and western CWA by the wee hours of Memorial Day. From earlier... Increasingly strong llvl theta-E convergence within the favorable upslope serly llvl flow regime across the Laurel Highlands and south-central mtns will concentrate the most numerous and heaviest showers and thunderstorms there through dusk. ML cape will also continue to slowly increase along the southern and western perimeter of our CWA late this afternoon and early this evening, within an area of nearly 1.5 inch PWAT air. FFG values are quite low, and the slow moving (and anticipated training/terrain anchored) convection will bring a distinct Flash Flood threat across our SW CWA through early this evening (with a lesser threat across portions of Scent PA that will be deeper into the cool llvl airmass0. Coordinated earlier with KLWX and KPBZ to post a Flash Flood Watch, and that runs until 02Z Monday for Somerset and Bedford counties. Again FFG values are lowest there with the 1-hr amounts needed being in the 1-1.5 inch range, and 3-hour guidance between 1.5 and 2.0 inches. Increasing and moderately strong/veering low to mid-level profile indicates that showers and isolated to scattered TSRA will spread northeast across the entire CWA this evening and overnight. locally moderate to heavy (0.75-1.00 amounts) appear likely, though the steady SW-NE progression of the rain tonight across the Central and NE zones should preclude any appreciable flood threat, other than some ponding and moderate rises on small streams/creeks. The warm front and upper shortwave embedded in the WSW flow aloft will translate to nearly 100 POPs for most of the CWA tonight (though portions of the far SE will see slightly lower POPs after sunset). High temps in the mid 60s to L70s will slide to only the u50s to l60s for overnight lows. Will mention the isold severe threat in the west and SC mtns in the HWO. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... Cold Front will be slicing through Central PA during the mid to late morning hours, crossing the Susq Valley during the early- mid afternoon hours. It should turn out to be a really nice day with just a westerly breeze in the west, but the slowing front may keep it muggier in the east and isold storms would then be possible in the east early in the aftn. Temps may be a bit higher than currently advertised due to some earlier clearing and the downslope effect (especially near the I-99/Route 220 Corridor. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... The long term period will be dominated by a large upper level low the will slowly moving through the upper Great Lakes and southern Canada. As that quasi stationary low slowly moves to the northeast, it will bring surges of cool moist air across the region. The first surge of cooler air moves across Monday night. This will bring showers in from the W/NW. However, any precipitation will cease as the night continues due to lack of diurnal heating. A reinvigorated boundary should bring a chance of precipitation through the northern half of PA. Several successive shortwave will move through mid to late week which will bring the possibility of 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. Late in the week the models begin to diverge on the location and timing of the upper level low so there is less confidence on precipitation late in the week. However depending where the boundary sets up there could be periods of showers Friday through Saturday, though currently should be mainly along the Southern border. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Not a lot of change for 00Z package. Poor night for aviation, given low CIGS in spots, showers and still some thunderstorms. Conditions should improve from west to east on Monday, as weak cold front moves across the area. .OUTLOOK... Tue...Chance of showers and thunderstorms. Wed...Chance of showers. Thu...No sig wx expected. Fri...Chance of showers and thunderstorms. && .CTP WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch until 10 PM EDT this evening for PAZ033-034. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...La Corte/Lambert SHORT TERM...Dangelo LONG TERM...Lambert/Ceru/Martin AVIATION...Martin is the U.S. government's official web portal to all federal, state and local government web resources and services.