Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 160328 AFDCTP Area Forecast Discussion National Weather Service State College PA 1128 PM EDT Fri Sep 15 2017 .SYNOPSIS... A large 500 hPa ridge with dominate our weather over the next 8 days. The only fly in the ointment is the trough and low pressure associated with Jose. This circulation will come close to the Mid-Atlantic region Monday into Tuesday before it meanders to the East. Behind this trough a very strong 500 hPa ridge with a closed 5880 m ridge is forecast to develop Friday into Saturday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... The last of the diurnally-driven showers have dissipated as of 02Z and the rest of the night should be dry. A calm wind and clearing skies will promote valley fog late tonight. SREF and downscaled NAM target the northwest counties for the most extensive fog development with localized visibilities near zero possible. Relatively humid air mass over the region will keep temps from falling much. Blend of latest guidance support mins from the mid 50s northwest to the mid 60s southeast. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Surface ridge over northwest Pa will result in limiting mixing and may allow patchy valley fog to persist until late morning over the northwest counties. Model data continues to show anomalous 500mb ridge axis across the eastern Grt Lks Saturday, while a weak trough lingers over southeast Pa. This upper troughing and associated pocket of cooler air aloft should result in isolated diurnally-driven showers during the afternoon/early evening. Ensemble mean 925/850mb temps edge up slightly from Friday, so expect max temps generally in the upper 70s to low 80s. The warm temps and dewpoints in the 60s will make it fell almost like mid summer. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... For the most part a 500 hPa ridge will dominate our weather. Our heights will drop as Jose approaches from the southeast and there could be some showers on the northwestern side of the storm and upper-level low which could affect southeastern areas. A shift of the storm to the east will reduce our chance of showers. As Jose moves away heights will rise and this should further dry us out. The GEFS forecasts a closed 5880 m ridge over us with near +2 sigma above normal heights by Friday and Saturday next weekend. Some more detailed information: The weak high at the surface should produce some patchy fog over the region Saturday into Sunday. Some isolated shower possible Sunday probably more convective QPF than any real forcing mechanism. Monday the flow is still weak and the PW is still low. But clearly the NCEP and CMC guidance produces some isolated convective precipitation so show slight to chance QPF in northwest. Nothing to hang your rain drops on. Tuesday several NCEP GEFS members bring rain into PA so we show chance to slight chance POPS in southeast. This is consistent with GEFS and CME EFS and other forecast offices. We are not confident in this fringe rainfall on the edge of Jose. If only knew the way for Jose. Wednesday as GEFS and CMC EFS pull Jose off New England coast our POPS drop. As this happens the heights rise fast and this should lead to a period of dry and unseasonably warm weather to end the week and start the weekend. Not sure why guidance in blends showed 20-30 POPS under a ridge. I lowered them. Big ridge means no big QPF events and definitely dry of Jose finds his way....east. And very warm for late September. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
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Still quite a bit of clouds over portions of the area. Thus backed off some on the duration of fog later on for the 03Z TAF set. More detail below. Weak sfc and upper level low will depart slowly to the east through this evening...maintaining VFR cumulus cloud deck into this evening. Spotty light showers possible before 22z. Winds will be very light and mainly from the NW/N. Fairly widespread fog expected again west and central areas with lcl IFR restrictions returns tonight, yielding on Sat to variable VFR clouds - and poss an isolated shower mainly in the SE. .Outlook... Sun...Patchy A.M. fog. Mainly dry with VFR conditions. Perhaps an isolated afternoon shower. Mon-Wed...Mainly dry with VFR conditions.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Fitzgerald SHORT TERM...DeVoir/Fitzgerald LONG TERM...Grumm AVIATION...DeVoir/Martin

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