A broken line of showers and isolated thunderstorms developed over central Pennsylvania during the afternoon of September 9, 2021, ahead of a secondary cold front crossing the region. One of these storms produced wind damage in western Franklin County.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS CTP wrote it up.
A broken line of showers and isolated thunderstorms developed over central Pennsylvania during the afternoon of September 9, 2021, ahead of a secondary cold front crossing the region. One of these storms produced wind damage in western Franklin County.
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 9, 1:34 PM EST, 1 hour 26 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 234 PM EDT Thu Sep 9 2021 .SYNOPSIS... Much cooler temperatures aloft, associated with an upper level trough, will move east across the region this afternoon through the midday hours Friday. This large scale weather feature aloft will create clouds and scattered to numerous showers this afternoon and early this evening across the mountains of the west. High pressure will then slowly build over the area through the weekend, with mainly dry weather and fairly seasonable temperatures. && .NEAR TERM /THROUGH TONIGHT/... Small, short-lived, but numerous SHRA and a few TSRA have popped over the wrn mtns and are moving ESE. Most cells living only 15-20 mins before passing on the baton. We did get a very decent downpour at the office with a gust to 39mph on the roof and 37mph at Beaver Stadium (We Are...windy). This first volley of forcing/short wave aloft will likely start dying down in 3-4 hrs as the sun gets lower. There is another spoke of vort in the axis of the trough, but it will arrive too late in the day to do much of anything past Warren/McKean Cos. Will keep PoPs in the nrn mtns for the first part of the night. Everyone else should clear out at first. The drier air and clouds and some light NW wind will try to keep fog from forming, but the cooler temps and partly cloudy sky overnight could allow the deeper valleys of the central mtns to fog up. However, the hill tops will likely not fog due to a bit of wind lasting most of the night. We have kept min temps close to blended guid there. Normally, we would undercut them a little on a night with better/more clearing and less wind expected. Mins will run from the u40s to the m50s. THV might get close to 50F if they calm down for more than an hour. && .SHORT TERM /FRIDAY/... The upper trough axis will have swung past our longitude by morning. Rising heights on Friday and breezy NW sfc wind will combine to decrease the morning clouds over the NW and lead to a mostly sunny and dry, but also slightly chilly, day. Maxes of m60s to l70s will be 1F to 10F below normals. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Heading into the weekend, a warming trend is expected as surface high pressure drifts just south of the Commonwealth and winds turn from northerly on Friday to westerly on Saturday and then southerly by Sunday. By Sunday afternoon, temperatures will top out at about 10 degrees above average, corresponding to sensible high temperatures in the upper 70s to mid 80s. The bulk of med range guidance tracks a dying cold front into the region late this weekend into early next week. Some disagreement is seen in med range guidance to the expected southern progress of the moisture-starved front. The front looks like it will stretch out W-E -- but at what latitude? The southward progression of this boundary will ultimately determine the chance for precipitation along and north of US-6 on Sunday and Monday afternoons, but have kept only slight chance PoPs in at this time. By Tuesday and Wednesday, considerable uncertainty remains in how progressive the upper level flow pattern will be, and whether there will be upper level troughiness or more ridging. At some point during the middle of next week, a surface cold front will traverse the region, but until then, have kept higher PoPs generally in the afternoons/early evenings, with the higher values north rather than south. The high heights (590+ dam 5H ridge) over the SE coast and western Atlantic Ocean will try to suppress storms ahead of the front, though increasingly unsettled weather will be the story through mid week. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... The SHRA around the area this aftn will be confined mainly to the wrn and nrn mtns, and could make a brief (<1hr) reduction to MVFR where they do form. Have added VCSH to almost all locations, but the most likely place to get vis/cig reduction from one would be JST/AOO/UNV. Just had one here at the office (close to UNV) with a G39mph right at 18Z. It appears that UNV didn't take the brunt of the cell. Shows just how localized these showers/storms are. No *widespread* restrictions to MVFR/IFR are expected until tonight over the mtns (BFD/JST) where MVFR cigs may return. The SHRA will dissipate this evening as the sun goes away. Fog could form if the cool air can settle into the deeper valleys of the nrn and central mtns. However, dewpoints in the u40s- l50s, lower clouds and some wind will help thwart a more widespread fog. The lower/MVFR clouds and any fog should dissipate early Fri AM and leave a mostly sunny and VFR day. It will be gusty with a 8-12KT NW wind and gusts close to 20KT on the hill tops. There is just a small (20pct) chc of a SHRA up close to LE generally N of BFD where the warmer lake water and cooler temps aloft could cause a taller cloud or two. Outlook... Sat-Sun...AM valley fog poss. Otherwise VFR. Mon-Tues...PM SHRA and associated restrictions possible north. Otherwise VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && SYNOPSIS...Jurewicz/Lambert NEAR TERM...Dangelo SHORT TERM...Jurewicz/Lambert/Fitzgerald LONG TERM...Dangelo/Banghoff AVIATION...Dangelo
Hazardous Weather Outlook National Weather Service State College PA 356 AM EDT Thu Sep 9 2021 PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-049>053- 056>059-063>066-100800- Warren-McKean-Potter-Elk-Cameron-Northern Clinton-Clearfield- Northern Centre-Southern Centre-Cambria-Blair-Huntingdon-Mifflin- Juniata-Somerset-Bedford-Fulton-Franklin-Tioga-Northern Lycoming- Sullivan-Southern Clinton-Southern Lycoming-Union-Snyder-Montour- Northumberland-Columbia-Perry-Dauphin-Schuylkill-Lebanon-Cumberland- Adams-York-Lancaster- 356 AM EDT Thu Sep 9 2021 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...Friday through Wednesday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Sterling radar (KLWX), 104 km away, was scanning. The volume nearest the first event began at 20:01 UTC.
1 thunderstorm wind. Local standard time, as filed.
A thunderstorm producing winds estimated near 50 mph pulled some metal sheathing off of a roof on an out-building in Lemasters.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2021Every state in 2021This day in weather historyWarnings in Pennsylvania, September 2021
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: 973236.