Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182221 AFDCTP Area Forecast Discussion National Weather Service State College PA 621 PM EDT Mon Jun 18 2018 .SYNOPSIS... Heat and humidity will be broken by a cold front dropping down from the north tonight. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... As of 6PM, the squall line that fired along the lake breeze and trekked SE across the region is a weakened remnant of its former self as it moves through the lower Susq Valley. The storms were mainly garden variety summer downpours as they valiantly fought the very warm air aloft. The next round of showers and thunderstorms preceding the cold front is just north of the NY border and will drop into the Northern Mountains over the next 1-3 hours. There may be little or no thunder left in the convection preceding the front by the time it reaches southern PA late tonight. SPC MRGL risk of severe is painted into the northern half of the area for storms this evening and tonight. Moist llvl air, and initially weak WNW flow behind the cold front will lead to some low stratus (and at least light fog) over the northern mountains between midnight and daybreak Tuesday with some lingering scattered showers possible. The expected large percentage of cloud cover later tonight, and the weak llvl advection of dry air will lead to another very warm/muggy night over most of the region (except for the far northern zones where temps will slide into the low 60s late). Elsewhere, mins will range from the upper 60s to mid 70s. High PWAT air of "1.5-2.0" and additional TSRA will bring the chc for locally excessive rain and at least minor flooding with some of the larger TSRA/Storm clusters...mainly across northern PA where the precip intensities are likely to be the greatest before the convection starts to weaken later tonight as it sags south of Interstate 80. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Deep dry air advection in the wake of the cold front will lead to a much more comfortable day with respect to temperature and humidity as sfc dewpoints slide through the 50s across at least across the northern half to two thirds of the CWA during the day (and perhaps below 50F by late in the day across the Northern Mtns). Most model and short range ensemble guidance paints a generally dry day across the south Tuesday. However, NBM guidance still holds onto scattered showers/poss TSRA over our SW zones, so we left in approx 50 percent pops in there.. The push of dry air continues and almost everywhere over South-central PA late Tues/Tues night (and the Laurel Highlands will be below 60 by Midnight Tues night). Most of the showers should be shunted off to our SW for Tuesday night. Max temps Tuesday will vary from the upper 70s over the north, to the mid-upper 80s in the SE or still near to several Deg F above normal. Mins early Wed morning will range from the low- mid 50s across the northern tier, to the mid 60s in the south. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Stalled frontal boundary stretched out to our south looks to edge back northward midweek, bringing mention of tstms back into central PA. Activity looks to be mainly scattered, though storms will be more numerous across the southern tier. By Thu, building high pressure over the northeastern U.S. should push any lingering showers south of the area. Drier air pushing in from the north will allow lows to fall into the upper 40s over the northern mountains both Thu and Fri morning. As the high pulls off the East Coast over the weekend, returning southerly flow and a filling upper low over the midwest will bring moisture and a renewed chance of unsettled weather - mainly scattered showers - back into the area from the SW. Temperatures will remain close to June normals through this period. Hugh pressure builds in across the Great Lakes for early next week, bringing dry weather and cooler mornings. && .AVIATION /22Z MONDAY THROUGH SATURDAY/... Regional radar at 2130Z showing isolated showers/thunderstorms over the I-80 corridor of central Pa. A brief vis reduction is possible in this area through early evening, then models indicate these showers/storms will dissipate. Main focus will shift toward another line of thunderstorms entering northwest Pa around 00Z in association with an approaching cold front. Models indicate a brief vis reduction is possible over roughly the northern half of the state between 00Z-04Z, with less chance across southern Pa, as storms weaken late tonight. A plume of higher low level moisture, combined with upslope flow ahead of cold front, appears likely to produce a period of low (IFR) cigs over the northwest mountains (KBFD) late tonight and over the the Laurel Highlands (KJST) later Tuesday morning. For areas east of the Appalachians, the drying effect of downsloping flow should yield no worse than MVFR cigs early Tuesday morning from KAOO northeast through KUNV/KIPT and VFR conditions over southeast Pa (KMDT/KLNS). Improving and mainly VFR conditions are expected later Tuesday morning and afternoon as drier air pushes into the region from the north. Lingering areas of MVFR CIGS and high end MVFR vsbys in HZ or showers is possible near and to the south of a KJST to KAOO line - especially if a few of the more northern model solutions with the stalling frontal boundary verifies. .Outlook... Wed...Showers/cig reductions possible southern Pa. Thu...No sig wx expected. Fri...PM showers/cig reductions possible central mountains. && .CLIMATE... Record max temperatures for June 18th: Harrisburg:97 in 1957 Williamsport: 97 in 1994 Altoona:92 in 1994 Bradford: 87 in 1994 State College:94 in 1923 && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for PAZ027-028-036- 049>053-056>059-063>066. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...La Corte/Lambert SHORT TERM...Lambert LONG TERM...Evanego AVIATION...Fitzgerald/Lambert CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.