Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 180946 AFDCTP Area Forecast Discussion National Weather Service State College PA 546 AM EDT Tue Jul 18 2017 .SYNOPSIS... A stalled front will remain hung up over the northwest part of the state today and tonight. Pennsylvania will be on the northeast periphery of a building subtropical high over the Plains state the rest of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Satellite imagery at 09Z is showing widespread valley fog across much of central Pa, while stratus covers the Lower Susq Valley. Weak pressure gradient and resulting lack of mixing should allow patchy low clouds/fog to persist until late morning over parts of the Susq Valley. Scattered diurnally-driven thunderstorms should develop this afternoon along and south of stalled front, which remains hung up across the northwest mountains. Model soundings showing weak shear, indicating any storms will be of the pulse variety with little threat of organized severe weather. FFG values are running quite low across portions of the Susq Valley from recent rain, but PWATS not particularly high and convection-allowing models not producing excessive rain amounts, so feel threat of flash flooding is fairly low. Have bumped max temps upward slightly based on GEFS mean 850 temps, which support highs from the low 80s across the high terrain of the Alleghenies, to near 90F in southern valleys. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Scattered evening convection across the southeast half of the state should diminish after sunset, then patchy fog will again become the concern. SREF and downscaled NAM both indicating the possibility of fairly extensive valley fog late tonight. Model data showing subtropical ridge expanding eastward from the plains states by Wednesday, likely suppressing convection across most if not all of the forecast area. Will maintain just a slight chance of a late day pulse-type storm across the Laurel Highlands and the extreme southeast portion of the forecast area. GEFS 850 temps nudge up a bit Wednesday, likely supporting max temps from the mid 80s over the highest terrain, to the low 90s over the Lower Susq Valley. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... 18/00z medium range models depict a general east-southeast shift of the upper level ridge initially centered over the Central U.S. Fast west-northwest flow aloft on the northern periphery of the upper ridge will reside over the area into the weekend. The evolution of convection-producing waves within this belt of westerlies is depicted differently within various models and specifics such as timing and location will depend on details not well resolved until the very short term time frame. That said, the later periods will show a broadbrushed, redundant 20-50 percent POP with refinements expected at closer ranges. The other concern is for a period of hot/humid conditions across the Lower Susquehanna Valley with blended guidance showing at least 2 days of 90+F max temps with max heat index potential approaching 100F. The heat risk was added to the HWO. The hot temperatures should be eroded from the NW with time as the frontal boundary gradually sinks to the south in response to mean troughing developing late in the period. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... A stalled out weak frontal boundary extended from near KIPT southwest to KAOO early this morning. High amounts of moisture and wet ground from yesterdays numerous showers and scattered thunderstorms, near and to the east of this boundary, was leading to areas of low clouds MVFR to IFR cigs and 1 1/2-3SM vsbys in fog (especially at KIPT...and perhaps at KAOO as well where LIFR CIGs are likely through 13Z). Isolated to scattered restrictions in SHRA/TSRA will occur across much of the region during the midday and afternoon hours as convection fires up near and to the east of the aforementioned, slowly meandering frontal boundary. .OUTLOOK... Wed...No sig wx. Thu...Sct TSRA impacts, mainly NW half. Fri-Sat...No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Fitzgerald/Steinbugl AVIATION...Lambert/RXR is the U.S. government's official web portal to all federal, state and local government web resources and services.