Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 261730 AFDCTP Area Forecast Discussion National Weather Service State College PA 130 PM EDT Mon Sep 26 2016 .SYNOPSIS... A cold front will move through quickly later this afternoon and early tonight. After a dry day or two, the forecast becomes rather wet with a cut off upper low . && .NEAR TERM /THROUGH TONIGHT/... Considerably amount of clouds stuck in the ridge-valley system of central Pennsylvania this morning. Sunny to the west and sunny to the east and here I am, stuck in the clouds with you. A nice early season cold air damming (CAD) event. For the enthusiasts out there, the 1000 and 925 theta-e contour show this quite nicely this AM as does the HRRR/RAP dew point fields. All our clouds are in the gradient between the warmer air to our southwest and the cooler drier air to our northeast. I used the HRRR to texturize the clouds a bit and to better time the frontal rain headed our way. The coarse GFS/GEFS have too much light rain too fast. The real front and frontal clouds are well back in Ohio. Most of the eastern half of central PA should remain a rain free zone until later this evening. Showers will arrive in the west later this afternoon and the HRRR implies some enhanced echoes suggesting some modestly organized thunderstorms along the line of showers. But the weaken in central PA due to the CAD event. Pretty stable to the north and east. The HRRR has chance showers with a narrow cold frontal rainband by 18Z and central PA around 21Z reaching Harrisburg an hour to two either side of 00Z. The HRRR simulates what looks like a narrow cold frontal rainband which I timed above. The HRRR also shows the weak evolution of a wideband back in the cold air later this evening in central PA. This implies two shots of enhanced rainfall. The wide cold frontal band does not clear Harrisburg/York/Lancaster until after midnight as it grows in size and intensity. The GEFS too shows similar timing of maximum rainfall periods just to diffuse. It clears out our light rain by 0600 UTC tonight. The air behind the front should actual be quite dry and conditions will improve over night west to east. Precipitable water values drop about -1sigma below normal overnight behind the front. && .SHORT TERM /TUESDAY/... All the rain should be gone well before sunrise and our PW values should be well below normal. Some strong winds to mix down so should be a breezy day and on the cool side of normal along with very dry air. Thus it should be a pleasantly cool early autumn day. There is not real anticyclone behind this system. But the winds should diminish as we stabilize in the late afternoon and early evening. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Should be relatively quiet weather Tuesday night into Wednesday. But the cyclone and developing cut-off to our west and the boundary along the front to our southeast will impact our weather by Wednesday. PoPs should creep up in southeast Wednesday due to the frontal boundary. The deep cut-off low to our west will increase shower risk in western PA Wednesday afternoon. And by Thursday the big cut-off will likely bring us very cool and showery weather for a few days. Previous: The mid week period will bring the large upper level low through the Great Lakes and down into the Ohio Valley. The low will slowly progress eastward with model PWATS increasing through the latter half of the week. Couple this with the Southwesterly flow and will allow for an increase of POPS Through the second half of the week and into the weekend. This will make the forecast a little milder at night and slightly cooler in the day, but very nearly normal. Have kept up with the overall trend of increasing POPs for the latter half of the week and into the weekend. The upper low is currently progged to lift northeast, but probably not until then end of the long term period. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Updated the TAFS with the latest guidance and tweaked shower timing to the 16Z HRRR. VFR will dominate the rest of today. Someareas of MVFR in west as the front is entering westernmost PA this afternoon. There are considerable areas strong surface winds which could affect approaches. This front will bring a 1-3 hour shot at showers and isolated thunderstorms in the northwestern areas and mainly a 1-3 hour shot at showers in the central and east later this evening and early tonight. Tried to time this frontal passage over the next 12-15 hours. Expect 1 to 6 hours of MVFR and areas IFR with this line. Very dry air behind the front with only brief period of IFR/MVFR as the system moves to the east. Then conditions rapidly improve. VFR Tuesday though a breezy day. Wed should be the last good VFR day then more showery and cloudy conditions later in the week into the weekend suggest mix MVFR/VFR and locally VFR. Outlook... Tue...No sig wx expected. Wed...Showers/cig reductions possible late. Thu-Fri...Sct showers/cig reductions possible, esp w mountains. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Grumm SHORT TERM...Grumm LONG TERM...Dangelo/Ceru AVIATION...Grumm

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