Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 221008 AFDCTP Area Forecast Discussion National Weather Service State College PA 608 AM EDT FRI JUL 22 2016 .SYNOPSIS... Pennsylvania will be on the northern edge of a subtropical ridge into next week. An upper level disturbances and associated weak cold front across the great lakes will move southeast and cross Pennsylvania later this afternoon and tonight accompanied by isolated to scattered, mainly afternoon and evening showers and thunderstorms. Mostly sunny, very warm, and generally dry conditions will follow for the upcoming weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Very warm temps aloft (around 8C at 700 mb) resided over the state at 09Z, with even warmer mid-level temps noted further upstream across the Upper Great Lakes. Weak to moderate llvl positive theta-e advection will interact with the cfront, and a rather potent 300 mb speed max of 80-90 kts headed SE from the glakes to support a growing area of tsra over the next 3-4 hours. These storms will continue to move southeast across the very warm waters of Lake Erie and likely continue to strengthen as they move into a favorable low-level environment of llvl moisture and . After the early day activity fades across Northwest or Central Penn, we should see a 3 or 4 hour period of generally hot but dry weather. The fact that the storms will be moving steadily east (within a mean 30-40 kt low-mid level jet, there should be little threat of heavy rain/flooding problems. Ensembles point to an increase in the PWATs ahead of the shortwave and associated weakening cold front (that should make it to the the intersection with a developing lee trough somewhere across north-central PA or the Susq Valley). HRRR pushes the bulk of the activity (that was currently lighting up the north shore of Lake Erie) across the western southern tier of New York this afternoon, then drives it ESE into N. Central Pa and then the Poconos where SPC`s current day 1 outlook resides. This fcast track of the convection appears to be a little too far north...based on current regional WSR-88D Mosaic loop. Elsewhere across the fcst area, SPC painted in a very broad area of a MRGL Risk for severe weather from PA...west through the Ohio Valley and covering the central and southern Miss Valley. HRRR implies that much of the convection throughout the Central MTNS and southern PA will dissipate during the 13-16Z timeframe before firing up in a rather extensive line or lines from near KAVP...to KSEG and KLBE and KPBZ. 0-4 km bulk shear will only be about 15-20 kts...and EHIs are generally less that one inch. Therefore, the primary several weather threat should come in the form of multi-cell clusters. 8h temps rising to near 20C should translate to max temps this afternoon ranging from the m/US over the Alleghenies, to between 90 and 95F elsewhere. The heat, combined with rising dewpoints, should result in widespread heat indices in the 90s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
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After a few scattered showers and thunderstorms...mainly early tonight...cooler and noticeably drier air will filter southward into the region. Lingering areas of stratocu and alto cu and a light westerly breeze will keep min temps mainly in the 60s...to lower 70s in the south.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/... Big story in the extended fcst is expected heat wave lasting into early next week, as axis of subtropical ridge briefly shifts from the plains to the northeast conus. Anomalous upper lvl ridging building over PA should bring hot and mainly dry wx this weekend, as warm temps aloft suppress convection. Next chance of shra/tsra for most of the area comes Monday ahead of shortwave working across the Great Lakes. However, any rainfall Monday is likely to do little to stem the dry pattern we have been in. Latest GEFS mean qpf is up to a half an inch at most. 12Z ECENS/NAEFS mean 8h temps are near 22C Saturday through Monday, indicating the potential of several days in a row with highs in the 90s in the valleys. The hottest temps look to be on Saturday as latest GEFS gives high temperature anomalies in the +4 standard deviation and have slightly backed off on Sunday. Have adjusted Max temperatures accordingly. Heat indices around 100F appear possible by Mon across the Susq Valley, as higher dewpoints are advected into the area. Overnight lows are also a concern as the area doesn`t cool off at night through the weekend with Southern PA lows in the 70s with highest readings Monday morning. Some modest cooling appears likely by Tue/Wed of next week behind weak cold front. However, temps still likely to remain somewhat abv normal within a generally zonal flow. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... VFR conditions should prevail through the majority of the period. Area of showers/TS developing northwest of Lake Erie may reach the BFD terminal area 12-15Z. Isolated to widely scattered thunderstorms remain possible across the entire airspace this afternoon through the early evening. Limited coverage/low confidence will preclude TS mention for now and will reassess with the full suite of near term meso guidance by the 12z scheduled issuance. The greatest risk for strong to severe TS appears to be across the northeast airspace in ZNY sector. OUTLOOK... SAT-SUN...Early morning fog possible...otherwise no sig wx. MON-TUE...Restrictions possible with a chance of SHRA/TSRA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Ceru AVIATION...Steinbugl

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