Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 290842 AFDCTP Area Forecast Discussion National Weather Service State College PA 442 AM EDT Mon May 29 2017 .SYNOPSIS... A cold front will stall out over central and eastern PA today. Low pressure stalled over northern Ontario during mid-week will lead to a period of slightly cooler than normal temperatures and a series of fronts passing through which will make many chances for showers through the week. && .NEAR TERM /UNTIL 5 PM THIS AFTERNOON/... Widespread SHRA rolling across the area now. This should be the last huurah for the heavy rain, as a strong short wave trough/MCV is easily seen in the radar loops zipping northeast through northern PA. The surface front(s) are just about washed into one general trough with it`s axis over far western PA at 08Z. This trough should push eastward another 150 miles, but looks like it stalls out right over the Susq River. Showers should become more scattered shortly in the west with little additional rainfall after 5 or 6 am. This will be welcome news for there is some minor flooding on-going in Clearfield Co. RAP now has a decent handle on where the precip is and the movement of the cells/elements. IR sat pics show that the convection moving into the Laurels has cooling tops, and will continue to produce some heavier rain rates. We do have a high confidence in the RAP forecast of rain placement & rates for the next few hours. Not much lightning left in the showers - and most of it is confined to just the Laurels. Expect that the showers will be done across the western 1/2 to 2/3rds of the CWA by 10 or 11 am. But the stalling of the sfc trough means there will be a focusing mechanism in place. If the sun breaks through and there can be some good heating in the Susq Valley, there could be a line of showers (maybe thunder) develop later today. Across the west, the air will dry out a little with a west wind of 10-12 MPH and a higher gust possible this aftn. Maxes will be highly dependent of the amount of clearing that can develop. RAP and NAM llvl RH plots yield a less-than-sunny forecast for the eastern third and over the Alleghenies. However, the late May should combine with the wind/mixing to make it pretty sunny in the western half of the area this aftn. The clearing would come late in the day for the east, and have nudged temps down a little there. && .SHORT TERM /5 PM THIS AFTERNOON THROUGH 6 PM TUESDAY/... Brief ridging will allow the skies to clear over most of the area this evening, and residual moisture may lead to areas of fog, especially in the eastern valleys. Mins will dip into the 50s for most, as the dewpoints will be the bottom limit. A weak sfc trough will be pushed into the area from the northwest tonight. 8H temps fall a bit over the NW. Heights fall just a little, too, so some precip is possible before sunrise Tuesday over the northwestern third of the area, but it should be light. The trough begins to catch the stalled trough over the eastern counties. The southerly or southeasterly wind will yield good convergence and will crank up some showers and thunderstorms. Have painted high POPs for the area, but the amount/severity of destabilization is in question with the clouds in the NE early in the day. NAM cranks out 1500joules of CAPE and LI drops to -2 or so in the mid-day and aftn on Tues. SPC marginal Risk of svr wx for Day 2 (Tues) is painted across our eastern half, focused on the peak heating time. Will continue to mention this in the HWO. && .LONG TERM /TUESDAY 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. 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 Wed and 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 /08Z MONDAY THROUGH FRIDAY/... Adjusted thunder for 03Z TAF 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... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...Lambert/Ceru/Martin AVIATION...Martin

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