Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 251151 AFDCTP Area Forecast Discussion National Weather Service State College PA 751 AM EDT Thu May 25 2017 .SYNOPSIS... Soaking rain this morning will become more showery later today with a few strong thunderstorms possible mainly across south- central PA. Scattered showers will linger into Friday followed by a period of mainly dry conditions Friday night into Saturday. Showers and thunderstorms will likely impact the area Sunday into Memorial Day. Today will be the coolest day this week with temperatures rebounding through the holiday weekend. && .NEAR TERM /THROUGH TONIGHT/... 10Z: Band of heavier rain focusing over the western 1/2 of the CWA early this morning. Highest rainfall totals in the past 12 hours are concentrated over this area with max rainfall amounts around 1 inch over parts of the Laurel Highlands. Previous: All near term HIRES guidance shows steady light to moderate rain overspreading Central PA through 12z. Peak rainfall intensity between 09 and 15z still looks good coincident with max H85 mflux anoms and strong SE LLJ. Multi- model derived QPF amounts between 0.50 and 1 inches expected through midday with areas of 1"+ amounts in the southern Alleghenies aided by orographics and robust dynamics. Negligible instability will inhibit short-term rain rates resulting in a soaking rain with no runoff issues anticipated. The steadier rain should lift over the northern 1/2 of the area later this morning with overall mode of precipitation becoming more showery this afternoon with partial sunshine/cloud breaks expected in- and- out of shower spells. Occluded front pushes north of the Mason-Dixon line this afternoon which should allow for at least modest destablization with cloud breaks most likely across south-central PA. SPC has expanded MRGL risk northward into this area with thinking that thunderstorm development will concentrate near the frontal boundary over south-central PA. Instability is not that great but shear profiles are supportive of at least low risk severe probs. There is also plenty of large scale forcing to work with given strong height falls/negative tilt trough and favorable left-exit region jet dynamics. Will include risk for isolated strong/severe storms in HWO. Anticipate a gradual decrease in shower activity tonight into early Friday morning with consensus max POPs focused over the far NE and SW portions of the CWA. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Broad cyclonic/west-northwest flow on southern end of exiting upper trough will support terrain-enhanced showers on Friday before precip winds down Friday night/AM Saturday. A lower- amplitude but moderately strong westerly (zonal) mid level flow will set up in the wake of the departing upper trough with modest height rises/weak will ridging aloft into the weekend. A warm front is progged to extend east from surface low in the western Ohio Valley to the mid-Atlantic coast on Saturday. Central PA should reside on the north/east fringe of high instability convective corridor/MCS type pattern expected to evolve from the central and southern Plains to the southern mid- Atlantic coast into Saturday night. The greatest risk for scattered thunderstorms remains over the SW 1/4 to 1/3 of the CWA which is consistent with previous fcsts. SPC has introduced a MRGL risk into this area for D3. The remainder of the area should see a mainly dry start to the holiday weekend but will maintain slight chance POPs. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... The large scale pattern will evolve into a broadly cyclonic flow regime by Monday with upper trough parked over the Great Lakes and southeast Canada into midweek. The aforementioned warm front will lift north across the area on Sunday followed by a series of weaker cold front associated with shortwave trough rotating around parent upper low centered to the south of Hudson Bay. Ensemble blend still supports max POPs on Sunday/Sunday night into Monday with some additional shower opportunities into midweek as series of shortwaves rotate around mean upper trough. Temps should average pretty close to normal/seasonal to close out the month of May. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... Low pressure located over Ohio will bring a steady rain with widespread IFR/low MVFR cigs to central Pa this morning. The rain will taper off from south to north during the late morning hours as a warm front works into the region. Rapidly improving cigs and a wind shift from east to south are likely as the warm front arrives during early to mid afternoon in the south and late afternoon in the north. A few evening tsra could form in the unstable air mass south of the warm front, so isold tsra impacts are possible across the southern half of Pa. Winds will shift to the west this evening, as the low pressure system passes north of Pa. Residual low level moisture ascending the Allegheny Mtns is likely to result in IFR cigs at BFD/JST by late this evening, while downsloping flow results in more favorable cigs further east. Across eastern Pa, light wind, wet ground and light winds could result in areas of fog late tonight. .OUTLOOK... Fri...AM low cigs/showers likely BFD/JST. Sat...AM fog possible BFD. Sun...Showers/reduced cigs possible, esp Sun night. Mon...AM low cigs poss west. Sct PM tsra impacts poss east. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...Steinbugl AVIATION...Fitzgerald

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