textproduct: State College

WHAT HAS CHANGED

* Increased rain chances across the northern tier tonight into Thursday morning. * Elevated frost risk beginning Monday night continuing through Tuesday night with cooler temperatures and light wind.

KEY MESSAGES

1) Showers across the northern tier overnight into Thursday, trending closer to climatological averages to begin October.

2) Frost/freeze concerns across portions of central Pennsylvania early next week, beginning on Monday night and continuing through Tuesday night.

DISCUSSION

KEY MESSAGE 1: Showers across the northern tier overnight into Thursday, trending closer to climatological averages to begin October.

An upper-level trough will bring some light rain across the northern tier overnight into Thursday morning. At this time, best odds based on a combination of NBM/HREF guidance hones in on areas north of Interstate 80 as the most likely to experience rainfall overnight. Some members of hi-res model guidance do indicate that rainfall could reach as far south as a JST/RVL/ZER line; however, forecast continues to outline areas north of I-80 as the most plausible to receive measurable rainfall. In terms of rainfall amounts, generally light rainfall is expected with maximum rainfall amounts overnight topping out near 0.10".

More widespread rainfall is projected by all model guidance along a cold frontal passage. Timing remains fairly consistent between model guidance, with rainfall beginning closer to sunrise on Friday. Based on more recent model guidance, areas west of US-219 could experience first raindrops just ahead of sunrise, thus have sped up mentions of rainfall in the most current forecast package. Guidance remains fairly consistent on the cold front diving southeast throughout the day on Friday with rain chances beginning to exit the forecast area Friday evening. Instability associated with this frontal passage appear to be minimal; therefore, no thunderstorm mentions in the forecast package.

Outside of a wave tracking south of the region on Sunday, tranquil weather conditions are expected for the region this weekend. With regards to the wave, best chances for precipitation will be south of the Pennsylvania-Maryland border but cannot completely rule out a shower south of the Turnpike on Sunday, especially late Sunday morning into the early evening hours. Any additional rainfall will be light, before dry conditions prevail Sunday night and continue through the end of the forecast period.

------------------------------------------------------------- KEY MESSAGE 2: Frost/freeze concerns across portions of central Pennsylvania early next week, beginning on Monday night and continuing through Tuesday night.

Early next week, Canadian high pressure begins to build into the region, bringing much cooler air and dry weather to the region. LREF ensemble guidance outlines 850mb temperatures trending close to 0F across portions of northern Pennsylvania as early as Monday night, outlining the cooler temperatures that are expected for the beginning of the week. This high pressure will lead to very light wind and mainly clear skies across much of central Pennsylvania, so the biggest question mark with respect to frost will be how low temperatures get and if this is sufficient for frost formation. At this time, current forecast outlines MinTs closer to freezing north/west of the Allegheny Front confidence is higher in some frost/freeze concerns. Further south/east, there is a larger spread in guidance with respect to temperatures, so confidence remains lower; however, generally would urge those with agricultural interests to continue to monitor the forecast closely this weekend into the beginning of next week.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Mid/high-level clouds (VFR ceilings) will continue to overspread the Commonwealth this evening as moisture flows around a ridge centered across the southeastern US. Scattered showers will move across the Northern Tier (mainly KBFD, with spottier showers at KIPT) through Thursday morning as a shortwave moves along the northern periphery of the ridge, while subsidence will keep rain-free conditions in place elsewhere. These showers may be capable of brief visibility restrictions, mainly to around 4SM, as PWATs climb to around 1.5-1.75" over the Northern Tier. However, relatively dry air in the low levels (925 mb RH to 50-75%) will help to mitigate against rain- related visibility drops. In addition, overnight visibility restrictions due to river/valley mist/fog may occur east of the Alleghenies (KLNS/KMDT/KIPT/KUNV), especially downwind of the Chesapeake Bay (KLNS/KMDT) where light southerly flow at the surface may draw in moisture overnight.

Showers across N PA will taper off through Thursday morning as the shortwave exits the region, with building heights helping to keep additional disturbances northwest of our area during the day. Moreover, any morning mist/fog will dissipate by around 14-15Z Thursday. Otherwise, prevailing VFR is expected during the daytime Thursday with S/SW winds of around 5-10 kts. Winds may occasionally gust to around 15-20 kts across the western terminals (KBFD/KJST), where the pressure gradient will be tighter on the periphery of high pressure over the Western Atlantic.

Outlook...

Thu Night-Fri...Cold FROPA with showers along the front. LLWS possible, especially northern and western TAF sites.

Sat...VFR favored behind the FROPA. AM fog possible.

Sun...Restrictions possible as a weak low pressure system develops along the residual frontal boundary over the Mid- Atlantic. -RA possible, more so across southern and eastern PA.

Mon...Dry conditions with VFR prevailing.

CLIMATE

Soggy September Soaker... September 2026 (MDT) precipitation rankings IPT: 11th wettest (6.84") MDT: 26th wettest (4.72") AOO: 9th wettest (5.58") BFD: 10th wettest (4.85") JST: 3rd wettest (7.31") *since 2000 STC: 6th wettest (7.90")

CTP WATCHES/WARNINGS/ADVISORIES

None.