Area Forecast Discussion
Issued by NWS State College, PA

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382 FXUS61 KCTP 281042 AFDCTP Area Forecast Discussion National Weather Service State College PA 642 AM EDT Sun May 28 2017 .SYNOPSIS... A warm front will approach from the south today as a cold front approaches from the west. The cold front will pass through later tonight and early Monday. Low pressure will become stalled over northern Ontario during mid-week and will create a slightly cooler than normal and unsettled stretch of weather. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Sunrise special fog obs with fog getting worse at many ob sites. Will issue Dense Fog Advy for the south for the next few hours. Otherwise, the showers to the south have not made it north of WV and may dissipate totally before reaching the CWA. Prev... Fog and some low stratus make it murky this morning, especially in the southern tier. Some fog has also creeped into the rest of the area. This was expected, but the more interesting aspect of the weather this morning is the development of a cluster of showers and thunderstorms over northern WV that are headed this way steadily. The instability there is more likely aloft and right over or NE of the warm front. The dewpoints are much higher there than central PA, and it is all moving this way. We do expect that the convection will wane some as it works NE and farther from the good sfc dewpoints. But, scattered showers are in the forecast for the Laurels this morning. The upper level feature associated with this cluster will doubtlessly linger and will likely be a force in popping additional showers later this morning on the high terrain of central PA. Destabilization is most likely to the west of the CWA first. The fog and stratus around locally will keep heating slow this morning. But, when we break out and in those spots which do not have lower clouds this morning, we`ll see showers spread out and cover much of the area by sunset. The guidance trend recently is for more showers more quickly/earlier in the day. Almost all models and members of the various ensembles make storms over the Alleghenies before noon. A likely scenario is that the mountain tops will destabilize first and convection will drift NE. Wind profile is not terrifying, WBZ about medium or perhaps a little lower, and heating will be questionable. This does not bode well for severe storms, but the storms moving into the CWA from the west out of the warm-er sector will have some punch. MRGL risk includes Warren to Chambersburg and all areas SW, and there is a slight risk for Somerset Co. While this delineation is rather specific, in reality, it may be an even sharper drop off (perhaps only 20 or 30 miles) from a location where storms will almost- certainly be severe to a place where storms will not be severe at all. Will mention the isold severe threat in the west and SC mtns in the HWO. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... PWAT goes up to about 35mm before noon in the west, and this maximum slides to the east during the late aftn and evening. Storm motion to the NE is fairly certain but slow. The low level flow is very light and out of the SE at first, so the cells may not move far and MBE vectors will be short during the evening. So, expect a few heavy rainers. Widespread showers and storms will occur this evening and through the night. The NAM had trended faster with the CFROPA, but has reversed with the 06Z run. Now, this puts it more in line with the other guidance, but it may be a temporary thing. If the slower models come to fruition, the front will be half way through the CWA at 12Z and little if any showers are expected after noon in the east. The front does not hurry along on Monday, though. It should turn out to be a really nice day with just a westerly breeze in the west, but the slowing front may keep it muggier in the east and isold storms would then be possible in the east early in the aftn. Temps may be a bit higher than currently advertised due to some earlier clearing and the downslope effect. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A secondary surge of cooler air moves across Monday night. This will ring showers in from the W/NW. However, timing is against these surviving too far to the east. POPs during this midweek period will be painted as chc - translating to scattered showers with preference for the majority of the QPF (albeit quite light at that)to be across the typical west-nwrly flow upslope prone areas of the Laurel highlands and NW mtns. The chance for any thunder will be very minimal Tuesday through Thursday. Generally dry NW flow occurs late in the week into next weekend as a 1020 sfc high over the upper midwest Friday evening builds SE twd the region. Pops Thur night through Fri night will be 30 percent or less. After our bout of coolish weather with temps several Deg F below normal Sunday and Monday, GEFS mean temps rebound back to near or slightly above normal (even under slightly cooling 850 mb temps) for Tuesday through at least Thursday. ECENS mean temps are several deg warmer than the GEFS and Nat`l Blend of Models temps. leaned closer to the cooler solutions based on the few-svrl deg C of cooling aloft with near to slightly below 850 mb temps. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Fog developing in earnest across much of the region at 07z. IFR to LIFR conditions exist across much of the region, but there are some notable exceptions, such as KBFD and KIPT where conditions are still VFR. While expecting fog development at KBFD soon given no T/Td depression, fog may hold off at KIPT as T/Td still showing 4 degrees of spread. Model guidance actually supports limited fog at KIPT. Did include some MVFR restrictions at KIPT at this issuance. Early low clouds/fog will begin to lift after 12Z, with VFR conditions expected in most locations by afternoon. However, there is at least some potential of a moist sse flow into the mountains creating a MVFR stratus deck along the east slopes of the Appalachians from BFD south through UNV,AOO and JST. The other area of concern will be isold tsra impacts across the western airfields associated with a warm front pushing into the region. .OUTLOOK... Mon...AM showers/low cigs possible. Tue...No sig wx expected. Wed...Slight chance of showers/reduced cigs. Thu...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...Lambert/Ceru AVIATION...Jung

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