Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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028 FXUS61 KCTP 290308 AFDCTP Area Forecast Discussion National Weather Service State College PA 1108 PM EDT Fri Jun 28 2024 .SYNOPSIS... Low pressure will track north of Pennsylvania this weekend, with the attendant warm front lifting through the state Saturday and the trailing cold front coming through Sunday. A large high pressure system will build into the region early next week, then a dying cold front will likely push in from the Great Lakes and stall out over the area late next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A building low amplitude upper ridge over the Mid Atlantic region should provide most of Central PA with dry and mild conditions overnight. However, a weak shortwave approaching from the Upper Midwest will bring the chance of late night showers across the northwest part of the forecast area. A developing southwesterly low level jet and surging pwats ahead of the shortwave will overrun a slow-moving warm front over Western PA, bringing the best chance of showers and a slight chance of tsra to the N Mtns between 06Z-10Z. High pressure passing off of the New England coast will result in an increasingly moist low level southeast flow across the region overnight, likely resulting in developing stratus, especially where the flow is forced to ascend the higher terrain of Central PA. The increasing cloud cover/low level moisture, combined with an active south-southeast breeze, will result in much warmer conditions than last night with min temps in the 60s. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... A low amplitude upper trough will approach from the Grt Lks this weekend, with the associated surface low passing well north of PA through Southern Ontario/Quebec. The attendant warm front is progged to lift through Central PA Sat PM and the trailing cold front should slice southeast across the forecast area during the daylight hours of Sunday. GEFS pwats surge to +3SD above climo Saturday, as the warm front works into the region. Diurnal heating of the moist and increasingly unstable airmass along and west of the advancing warm front, combined with a belt of 50kt mid level flow across Northern PA, should set the stage for the potential of strong to severe thunderstorms during the afternoon and evening hours. Convection-allowing model guidance indicates the focus of the showers/tsra will be across the NW Mtns during the morning and early afternoon, then expand into the southeast part of the forecast area during the PM hours, as the upper trough and plume of highest pwats shifts east. Model soundings indicate there will be a good deal of cloudiness Saturday, especially over the north-central mountains, where model RH profiles indicate stratus could linger into the early afternoon ahead of the approaching warm front. However, even modest diurnal heating should yield capes in the neighborhood of 1000 J/kg Sat afternoon per latest ensemble output. The moderate instability, combined with progged 0-6km shear of 40-50kts, is more than sufficient to support organized strong/severe convection Sat PM with a few supercells and an isolated tornado possible, especially across the northwest half of the forecast area, where HREF UHEL values are highest and STP values peak near 2. The unstable environment,paired with anomalous pwats, suggests locally excessive rainfall/flash flooding is also possible Sat PM. The area of most concern is across the N Mtns, where FFG values are lowest and where latest HREF supports localized amounts of 3-4 inches. If 00Z guidance remains bullish over Northern PA, a short fused FF watch may be needed. Much higher FFGs will be a limiting factor to reduce the flood risk farther to the south and east across the CWA (where D0 and D1 drought conditions exist). Latest model guidance indicates the bulk of the convection will shift east of the region late Sat night, as the lead shortwave and plume of highest pwats exit the state. However, passage of the surface cold front will bring the chance for another round of convection Sunday. Locations most likely to see potential strong/svr t-storms are over the southeastern part of the CWA due to a fropa coinciding with peak heating of the late afternoon. Once the cold front clears, the door will be open for another seasonably cool/dry airmass to invade the Commonwealth. This will result in a less humid and comfortably dry start to July on Monday. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... A fair and cool Monday night looks likely as high pressure and associated dry airmass build directly over PA, resulting in efficient radiational cooling and min temps several degrees below normal. Fair and warmer weather is expected Tuesday into at least the first half of Wednesday, as upper level ridging builds over the state and surface high drifts offshore. All medium range guidance tracks a weakening shortwave well north of PA late Wednesday into Thursday. The dying cold front is likely to sag into the state Thursday and stall out in the vicinity of PA through Friday. Falling heights/surging low level moisture ahead of the front could support scattered convection as early as Wednesday afternoon over the northwest half of PA. However, a better chance of showers/tsra areawide will come with the arrival of the front Thu into Friday. Early best guess of late week rainfall based on ensemble plumes ranges from 0.25 to 0.75 inches, with the highest amounts over the N Mtns and least in the south. Heat and humidity should peak ahead of the front Wed-Thu. Ensemble mean 850mb temps surging to near 20C indicate max temps could reach the low to perhaps mid 90s in the Lower Susq Valley Thursday, with high humidity pushing heat indices into the mid and upper 90s. Ensemble plumes suggest slightly cooler daytime temps late week, due to more clouds/showers. However, high pwats in the vicinity of the stalling front should result in muggy nights and above normal min temps the entire second half of next week. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Wind will stay up overnight out of the S/Se for most terminals. The LLJet of 40-45KTs rolls up from S to N over the Alleghenies. 40+KT of LLWS is certain for BFD and JST. The ceilings will lower to IFR over the east (80pct chc) as the SE flow brings in very high Atlantic moisture. Over the west, a warm front should be on the doorstep at 12Z and a few -SHRA or just plain -RA will start to fall over the NW third/half of the Central PA airspace after midnight and make the nrn tier damp/wet by sunrise. Cigs look like they should be a little higher over the W than E overnight according to MOS and HREF vsby potential progs. The low stratus is expected to lift and become broken to scattered in the morning over the S, and gradually work northward a bit in the mid-day and aftn. Numerous TS/SHRA will be popping up over the NWrn third of PA in the and thunderstorms develop later on Saturday. High moisture will make the potential for very heavy rain and very low vsbys in the TSRA. TSRA will continue pressing SE thru the evening and first half of the night Sat night. The chance for showers and storms will linger across the southeast Sunday as a cold front drags it`s feet moving through the area. There could be fog Sat night in the NW (BFD), but that will depend on the amt of clearing. IFR from overnight/AM fog (Sun morning) at BFD is only a 40pct chc at this point, and lower elsewhere as not much clearing is expected elsewhere. Outlook... Mon-Tue...Dry weather with VFR conditions except perhaps some AM valley fog N. Wed...PM TSRA moving across from W-E. && .CLIMATE... Through 6/27, June ranks as the second warmest on record at Harrisburg with an average monthly temperature of 76 degrees or +3.8 degrees above normal. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald/Steinbugl LONG TERM...Fitzgerald AVIATION...Dangelo CLIMATE...Steinbugl