Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 250920 AFDCTP Area Forecast Discussion National Weather Service State College PA 520 AM EDT MON JUL 25 2016 .SYNOPSIS... A cold front will push southeast across Pennsylvania late today and tonight...accompanied by a likelihood of showers and scattered TSRA. High pressure will return for mid week with continued warm temperatures. Temperatures may trend back to near or slightly below normal over the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A hot and humid airmass will be in place across the region today...ahead of a cold front currently extending from southern lower Michigan...SSWD to the Chicago area. Significant breaks in the high based strato cu and alto cu cloud decks will allow instability/ml cape to ramp up significantly this afternoon bringing the threat for a few clusters of potent thunderstorms to move quickly east across the region. The southern two thirds of the CWA is under a SLGT Risk for svr tsra today with the primary triggering mechanisms being the aforementioned cold front...and well-defined entrance region of an 80 kt upper jet that will be sliding over southern New York state and NWRN PA. By 18z, 2 or 3 areas of quite high...0-1 km EHI of 2-3m2/s2 develops across the Alleghenies of nrn and wrn penn, then shifts SE to the Lower And Mid Susq Valley and increases even a little more to pockets of 2.5 to 3.5 m2/s2. A couple of short-lived HP supercells...transient mini bow echoes and a few compact MCV are possible across much of the region today with localizedstrong/damaging wind gusts, and some instances of large hail. Lagging upper trough and sfc cold front (briefly elongating to a more west/east direction this evening into the first half of the overnight hours) will combine with the very high...2+ inch PWAT values to bring the threat of some training TSRA with highly localized very heavy rainfall of 2 inches plus within just an hour. Headwater Flash Flood Guidance values are extremely high and 4 inches plus for the 1-3 hour period, so at this point there isn`t a big concern for flash flooding. However, PWATs are just about as they head around this part of the country. Timing for the larger scale - bkn line of significant shra/tsra will be across the nw mtns between 15-18Z...then bisecting the state from NE to SW around 19z...before impacting the Lower Susq Valley mainly after 20Z. Patchy fog will occur through about 13z in some of the valleys in central and southern PA where the more widespread light to moderate rainfall occurred Sunday evening. Temps to start the day will range from he u60s across the mtns of northern and western PA, to between 70 and 75 degrees across the ridge and valley region of Central PA. Ens mean 8h temps support max temps today from the u80s across the Allegheny Plateau, to the m90s across the Susq Valley. The combination of heat and humidity warrants continuation and slight northward expansion of the heat advisory across roughly the SE half of the fcst area. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... The relatively weak sfc cold front will slide SE across the SE half of the state late today and tonight, accompanied by scattered showers and perhaps a few tsra early tonight. Clearing skies lower PWAT air, and a rather light WNW breeze of 5 kts or less could lead to some patchy dense stream/river valley fog...esp north late tonight and early Tuesday morning. low temps early Tuesday will vary from the l60s across the north...to the lower 70s across the SE zones. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Big story in the extended fcst is the likelihood for modest cooling by Tue/Wed behind the weak cold front. However, temps still likely to remain somewhat abv normal within a generally zonal flow. Midweek weather looks dry again, with just low pops for isolated tstms. Fri looks to be the next higher chance for tstm impacts areawide as another cool front progged to move through. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Fog starting to form in the places it rained in the last 24 hours. However, the thickest fog and lowest cigs are up in BFD where it did not rain. Model soundings and llvl moisture progs for the NW mountains keep the low crud in there until 8 or 9 am - when showers will start to form/move in from the west. There is a short wave trough moving through TOL/DTX at this time and it will touch off most of the SH/TSRA today. Timing from most sources would take most of the storms to our south by 00z. There could be some stronger/gusty storms over the southern terminals this aftn/eve, as heating and the approach of a longer-wave upper trough slides in right behind the first trough. Dewpoints do not dip all that much tonight, so fog is almost likely with some clearing and residual llvl moisture from the rain earlier. However, if there is enough time to dry it up before nightfall/clearing, we may not fog up. Other than some lingering showers in the evening/early night, it dries up for later tonight and right through Thursday. Don`t even expect much fog in the mornings of the mid-week. OUTLOOK... TUE-WED...VFR. THU-FRI...Mainly VFR. SCT PM SHRA/TSRA. && .CLIMATE... Record high for Harrisburg today is 99 degrees set in 1940. Record high for Williamsport is 100 set in 1934. && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 3 PM this afternoon to 8 PM EDT this evening for PAZ027-028-035-036-049>053-056>059-063>066. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Gartner AVIATION...Martin CLIMATE...Lambert

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