Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182000 AFDCTP Area Forecast Discussion National Weather Service State College PA 400 PM EDT Fri Aug 18 2017 .SYNOPSIS... A cold front will move through late today. An upper trough will move across the area on Saturday. Temperatures will stay above normal but rise even higher each day through Tuesday as a ridge builds aloft. Another cold front should trigger showers around mid-week and the week should end on a cooler note. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Numerous SHRA and a few TSRA now cover much of the SE. All is on track with the fcst. New SVR watch just issued to cover severe threat of mainly wind damage, but some spinners/right-movers are already occurring and there is a risk for brief tornadoes with such low LCLs and shear sufficient to make mini-supercells. Not much ltg right now due to warm temps aloft. Much of the area will be either worked-over (stabilized) or just plain out of the threat area withing the next 2-3 hours. Secondary line of showers over the NW is likely the front, but some additional development along that line or between the current area of storms and that line is possible. These storms should not be as active/dangerous as the first area. A tertiary line of showers/storms is then possible over the nrn mtns this evening, but without much instability and CAPE left, these should not be severe. Clearing is Low clouds could form along the western highlands after sunset. Some fog is possible - mainly in places that are getting the heavy rain and have little time to dry out but also clear out well. That would be the SE counties. Dewpoints will dip into the m60s in the NW shortly and down to around 60F tonight. The m70 dewpoints in the SE will likely only dip to the u60s for the overnight. Can`t see temps going below those numbers.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... The high pressure moving in finally clears everyone out in the morning. Any low clouds in the NW will dissipate nicely with the sunshine. The trouble there is that the lingering moisture, the passage of the upper trough and enhancement from a potent short wave coming around the base will meet up at peak heating. These factors and the wind field will generate multiple showers in the NW half of the area in the aftn. Some of these will make some good gusts - and some could get severe. A little small hail is also possible with colder air aloft than today. SPC does have that area in a MRGL risk for severe wx. The showers/storms will struggle to get past the Allegheny Front (roughly IPT-UNV- AOO line). Max temps will be right near normals. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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The mid range models are all in good agreement on the timing and strength of the passing shortwave Saturday night. Once that passes, the heights will rise and become quasi-zonal. This will bring fair weather to the region Sunday through Tuesday. Dry westerly flow will also bring warm summertime temperatures with Tuesday continually trending warmer. A new shortwave moving through SRN Canada will an bring an increasing chance for rain, possibly as early as Tuesday afternoon over western sections of the forecast area. There are differences in timing of the rain with the ECMWF suggesting it holds off until Tuesday night. Blended MOS POPs show a small chance of showers moving into western sections Tuesday afternoon, but the highest POPs are reserved for the overnight. Cyclonic flow aloft will then dominate the flow pattern through Thursday. The cool air aloft will help trigger a few mainly diurnal showers Wednesday and Thursday. The showers will tend to favor northern and western higher elevations. Temperatures will be significantly cooler for the second half of the week.
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&& .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... Storms all over the radar scope at 19z SE of UNV-IPT-AOO. Just a spot of showers in the N east of BFD. That spot is probably along the real cold front as there are lower dewpoints immediately to the west of it. Additional storms are possible in the west and central counties late this aftn, but most locations will remain dry and VFR. A final push of drier air will move through this evening and early tonight. Thus, a few shra are possible in BFD between 23z and 02z - but the other terminals should stay dry this evening and tonight. Fog is possible for most of the area tonight, but more so in the SE where it has rained and had clearing, but little time to dry. Lower clouds should form over the NW mtns tonight, but these should stop around the old AOO-UNV-IPT line. An upper level trough and rather strong forcing passing directly overhead in the cooler air aloft could make sct shra/tsra across the northern third/half of PA on Sat aftn. Much drier air will make for a mainly-VFR Sun-Mon with only valley fog in the AM a potential issue. .OUTLOOK... Mon...No sig wx. Tue-Wed...SHRA/TSRA poss. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...Ceru/La Corte AVIATION...Dangelo

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