Daytime heating during the afternoon and evening hours of September 23, 2025 allowed for convection to occur across portions of the Lower Susquehanna Valley in an environment with ample moisture and low steering flow aloft allowing for slow-moving thunderstorms. Thunderstorms produced a quick 3 to 4 inches of rainfall in Millersville, which prompted multiple instances of flash flooding in the…
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The episode as NWS CTP wrote it up.
Daytime heating during the afternoon and evening hours of September 23, 2025 allowed for convection to occur across portions of the Lower Susquehanna Valley in an environment with ample moisture and low steering flow aloft allowing for slow-moving thunderstorms. Thunderstorms produced a quick 3 to 4 inches of rainfall in Millersville, which prompted multiple instances of flash flooding in the vicinity of Millersville University.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS State College, PA wrote its last area forecast discussion before the first event at Sep 23, 1:57 PM EST, 3 hours 53 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 257 PM EDT Tue Sep 23 2025 .SYNOPSIS... * Muggy with above average temperatures to begin astronomical Fall * Periods of much needed rainfall expected through Thursday; rainfall signal is unclear for the weekend (leaning dry) * Dry pattern is likely to return by next week and could last into early October && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Downstream of a broad/weak mid level trough and embedded shortwave/vortmax crossing the WV/MD panhandle, low level clouds are blanketing areas along and to the NW of I-81 -- effectively keeping diurnal instability in-check across the western and central Alleghenies this afternoon. Expect sct showers to continue to track to the northeast across this part of the fcst area into the evening with temps holding in the 65-75F range. Meanwhile, plenty of sunshine has allowed for strong heating over the lower Susq Valley (80-82F at 17Z) which should erode remaining CIN by 18-19Z and allow for convective development into the early evening. Based on visible sat and CAPE trends, we would favor the extreme southeast zones/Lancaster Co vcnty with the best odds for a stronger storm/risk of locally damaging wind gust before activity weakens/shifts to the east later this evening after 8pm/00UTC. Hires models show a lull in the showers tonight, with the main focus shifting to areas of dense fog/low visibility into early Wednesday morning. Muggy/warm night by late September standards with lows 55-65F or +10-15 degrees above climo. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... Latest HREF/NBM shows very limited shower activity (not much if any rainfall) through Wed afternoon. Expect POPs to ramp from SW to NE later in the day into Wednesday night. Amplifying longwave trough stretching from the Great Lakes southward into the Lower MS Valley will send higher pwats into the area and promote rounds of showers and storms through Thursday night. On balance, the rain will be highly beneficial given the abnormal dryness (D0-D1 drought) and much below % normal precip departures over the past several weeks; however will need to monitor for locally heavy/repeat downpours that could lead to some minor/urban flooding concerns. && .LONG TERM /FRIDAY THROUGH TUESDAY/... There is still plenty of spread in the model data regarding the pattern evolution/configuration over the Eastern U.S. from late week through the weekend. Split flow to higher amplitude blocking solutions are possible outcomes to add to the high uncertainty/complexity along with 1 or 2 tropical systems off the Carolina/Southeast coast to factor into the mix. The precip signal is not particularly strong over CPA (highest in the southeast) -- but we are not ready to go all-in on a dry last weekend of September. Longer term trends do eventually favor the return of drier conditions/lower humidity by the start of next week into early October. This transition favors the return of warmer than climo max temps/daytime highs and cooler nights closer to the historical average. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... An upper level trough will move northeast today, enhancing large scale lift and impacting much of the region with a few more rounds of rain/showers and scattered thunderstorms. The greatest potential for brief strong wind gusts from the storms will be over the Lower Susq Valley and western Poconos this afternoon, where the prob of SFC based CAPE exceeding 1000 and 2000 J/KG is the greatest. Lowest CIGs and vsbys across the Lower Susq Valley will come in the 22Z Tue - 03Z Wed period as a cold front pushes through and will likely be accompanied by numerous showers and some embedded, moderately tall showers. Later tonight and Wednesday morning, a few breaks in the cloud cover will enhance radiational cooling and cause locally dense fog to form after 04Z Wed. Not much change with the pattern, weak systems will bring some showers and storms to central PA through Thursday and even some chance on Friday. Conditions trend drier by the weekend. Outlook... Wed-Sat...Multiple rounds of SHRA and PM TSRA (best chances Tue and Thu) with sub-VFR conditions expected. Sun...Low cigs/vsby in poss fog early. Improving to VFR later. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...Dangelo/Banghoff AVIATION...Lambert/Gartner
Hazardous Weather Outlook National Weather Service State College PA 915 AM EDT Tue Sep 23 2025 PAZ004>006-010>012-017>019-024>027-033-034-037-041-042-045-046-049- 241315- Warren-McKean-Potter-Elk-Cameron-Northern Clinton-Clearfield- Northern Centre-Southern Centre-Cambria-Blair-Huntingdon-Mifflin- Somerset-Bedford-Tioga-Northern Lycoming-Sullivan-Southern Clinton- Southern Lycoming-Union- 915 AM EDT Tue Sep 23 2025 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. PAZ028-035-036-050>053-056>059-063>066-241315- Juniata-Fulton-Franklin-Snyder-Montour-Northumberland-Columbia-Perry- Dauphin-Schuylkill-Lebanon-Cumberland-Adams-York-Lancaster- 915 AM EDT Tue Sep 23 2025 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and tonight. Scattered thunderstorms with a risk of locally damaging winds are possible this afternoon. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather.
The Dover AFB radar (KDOX), 154 km away, was scanning. The volume nearest the first event began at 22:47 UTC.
2 flash flood. Local standard time, as filed.
Water was reported to be across the roadway at Pleasure Road and East Walnut Street in the city of Lancaster.
Multiple reports of water across the roadway resulted in the closure of New Holland Avenue between Lancaster and Eden.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2025Every state in 2025This day in weather historyWarnings in Pennsylvania, September 2025
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1289344, 1289346.