Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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307 FXUS61 KCTP 231856 AFDCTP Area Forecast Discussion National Weather Service State College PA 256 PM EDT Sun Jun 23 2024 .SYNOPSIS... A cold front over the Great Lakes will sweep eastward across Central Pennsylvania this evening. A second cold front will push across the region late Wednesday, then a building upper level ridge is likely over the Mid Atlantic toward next weekend. && .NEAR TERM /THROUGH TONIGHT/... Increasing bulk shear and SRH is evident in radar signatures the last 45 minutes with cells gaining the propensity to rotate, and mature cells able to bow out over northern Tioga County and produce (warned) thunderstorm wind damage.The aforementioned parameters only increase through late afternoon as LCLs from roughly the I-80 corridor northward range from 550m to 900m. SPC evaluating for potential Watch, but we`re waiting to see where storms will be most likely to more consistently organize, so perhaps it`ll be beyond 19/20z but it`s even possible that severe threat remains isolated enough to preclude Watch issuance. Elsewhere, broken mid clouds have limited sfc heating, but still plenty of warmth and humidity farther south and east as a slow moving front sags into the region late this afternoon and evening. As we mentioned earlier, we`ve been focused on shear parameters as they increase through late afternoon, with latest HRRR runs indicating favorable 0-3km SRH exceeding 300m2s-2 in pockets, and low LCLs supporting warm RFDs and the potential for an isolated tornado or 2 over mainly north central PA. Trailing cold front crosses northwest PA this afternoon and reaches the central mountains this evening. Wide range of solutions from the CAMs, but NAM3km is handling things reasonably well and continues to indicate increasing coverage and intensity across western and central areas by late afternoon. Lee trough may finally support convection initiation shortly over the Susq Valley. Strong large scale forcing ahead of the upper trough, combined with +2-3SD pwats ahead of the cold front, supports fairly high POPs into the evening in the 60-90pct range. The increasing 0-6km bulk shear in the 30-40kt range, combined with progged CAPES in the 1000-1500 J/kg range, supports organized multicell clusters, a few supercells and perhaps even an isolated tornado. The best chance of a tornado appears focused over the N Mtns, where model 850mb winds and 0-1km shear is strongest. The HREF also projects STP values >1 across this area. Locally heavy downpours will also occur, but progressive storm motions should preclude significant flooding concerns in most areas. Dwindling showers/tsra should work east across the area this evening with the passing cold front, then much drier air is slated to arrive overnight. Breaking clouds are expected downwind of the mountains, but upsloping flow and low level moisture trapped beneath a subsidence inversion is likely to yield lingering stratocu across the Alleghenies. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... Relief from the heat comes Monday behind the upper trough with sfc dewpoints dropping into the 50s. A tight pressure gradient and steep lower tropospheric lapse rates should result in a very breezy Monday by late June standards. Bukfit soundings support afternoon wind gusts in the 25-30kt range over much of the region, which is significantly higher than NBM guidance. Fair and seasonable weather with diminishing winds are anticipated Monday night, as high pressure builds into the state. Latest NAMNest and SREF prob charts target the Alleghenies for late night valley fog. A warming trend emerges on Tuesday as surface high pressure builds across the Mid-Atlantic. Despite the warm-up into Tuesday, MaxTs in the lower 90s across portions of the Lower Susquehanna Valley will be the ceiling in this forecast cycle, where 10-20% of ENS members outline temperatures exceeding 90F during peak warming hours with less than 10% of GEFS members outlining temperatures exceeding 90F. Surging PWATs ahead of a sfc cold front begin to enter central Pennsylvania late Tuesday evening into Wednesday morning, where chances of precipitation return to the area. Deterministic model guidance has notably shown less coverage in precipitation Tuesday evening, and have limited PoPs towards the northern tier where the best moisture and forcing will be available. PoPs will begin to expand areawide through Wednesday, especially during the afternoon/evening hours where the best daytime heating will be available ahead of the cold front. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Showers and storms will gradually exit to the the southeast on Wednesday night as high pressure builds in. The midweek cold front will reset the cycle similar to what today`s cold front will do and usher in a similar stretch as Monday & Tuesday. Thursday and Friday will consist of about 48 hours of lower dewpoints, temperatures closer to average for this time of year, and plenty of sunshine. Afternoon highs in the 70s and 80s, overnight lows in the 50s and 60s (perhaps even upper 40s in the northern mountains Friday morning), and dewpoints below 60F will feel especially good with the persistent stretch of heat. As high pressure shifts to the east on Friday, southerly flow will support increasing temperatures and moisture into the weekend. The chance for showers and storms will also ramp up Saturday and Sunday as a warm front lifts across the region. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Multiple rounds/lines of storms are expected today across the region. The first round of showers is across northwest PA at 11AM and has struggled to produce lightnign at this point. That line of showers will begin to intensify during the early afternoon hours ahead of a cold frontal passage. There is higher confidence in SHRA/TSRA impacts at airfields across central PA after 18Z with continued daytime heating ahead of the front. While the bulk of the thunderstorm activity will be focused along the cold front this afteroon, a few storms may develop in the Lower Susquehanna Valley ahead of the main line and bring restrictions to MDT/LNS between 18 and 20Z. While ceilings will likely remain VFR across the east through the entire TAF period, most guidance suggests that MVFR ceilings will develop west of UNV as the storms move in. Brief periods of IFR will be possible in any thunderstorms. The HREF suggests around a 50% chance that these low ceilings stick around through most of the night at BFD and JST as winds shift to the west behind the front. Outlook... Mon...Predominantly VFR, with brief restrictions possible in scattered SHRA/TSRA as a cold front crosses the area. Tue...VFR, no sig wx expected. Wed...Restrictions possible in TSRA. Thu...AM SHRA/TSRA with restrictions possible, drying out late. && .CLIMATE... A heat wave will continue through the weekend with near-record temperatures forecast in some locations on Sunday. Daily record highs for Sunday June 23: 6/23 State College 91 (1966) Harrisburg 97 (1965) Williamsport94 (1923) Altoona 90 (1994) Bradford 86 (2013) The following records have been set during this stretch of heat: MDT: * A record high temperature of 99 degrees was set at Harrisburg, PA on Saturday, Jun 22, breaking the old record of 97 degrees set in 1988. IPT: * A record high temperature of 98 degrees was set at Williamsport on Friday June 21st, breaking the old record of 97 degrees set in 1923 and tied in 1933. BFD: * A record high temperature of 89 degrees was tied at Bradford on Friday June 21st, tying the record set in 2022. * A record high temperature of 90 degrees was set at Bradford on Thursday June 20th breaking the old record of 88 degrees set in 2012. * A record high temperature of 88 degrees was set at Bradford on Wednesday June 19, breaking the old record of 87 degrees set in 1987. AOO: * A record high temperature of 96 degrees was set on Saturday, Jun 22, breaking the old record of 91 degrees set in 1988. Highest Max Temperatures for Central Pennsylvania Observing sites for June (date of occurrence is in parentheses: State College 96 in 1952 (26th) and 1933 (29th) Harrisburg 100 in 1966 (27th), 1952 (26th), and 1934 (29th) Williamsport 104 in 1925 (5th) Altoona 97 in 1971 (28th) and 1953 (21st) Bradford 93 in 2022 (22nd) Longest run of consecutive days with max temp >=90 in June: State College 6 (24-29th 1966) /current streak=1/ Harrisburg 10* (19-28th 1943) /current streak=6/ Williamsport 9 (18-26th 1923) /current streak=6/ Altoona 8 (13-20th 1994) /current streak=6/ Bradford 1 (23rd 2024) /current streak=1/ *Harrisburg had a run of 11 days with temperatures greater than 90 degrees that started on 26th and ended on July 6th in 1901. && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT this evening for PAZ028-036- 049>053-056>059-063>066. && $$ SYNOPSIS...DeVoir/Fitzgerald NEAR TERM...DeVoir/Fitzgerald SHORT TERM...DeVoir/Fitzgerald LONG TERM...Dangelo/Banghoff AVIATION...Banghoff/Bauco CLIMATE...Evans/Steinbugl/Colbert