Scattered showers and thunderstorms develop during the early afternoon hours of July 17, 2021 across western Pennsylvania and in the Lower Susquehanna Valley in an anomalously humid airmass ahead of an approaching cold front. The storms over the Lower Susquehanna Valley developed on a weak boundary in a high CAPE environment, and produced sporadic wind damage before moving to the east.
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.
Scattered showers and thunderstorms develop during the early afternoon hours of July 17, 2021 across western Pennsylvania and in the Lower Susquehanna Valley in an anomalously humid airmass ahead of an approaching cold front. The storms over the Lower Susquehanna Valley developed on a weak boundary in a high CAPE environment, and produced sporadic wind damage before moving to the east. The storms over western Pennsylvania eventually congealed into a broken line that progressed eastward across central Pennsylvania and had imbedded regions of damaging winds and very heavy rain. One hail report was received from beneath a particularly tall cell that developed over Blue Mountain just west of Marysville in Perry County. Flash flooding from these storms was reported across McKean, Dauphin and Tioga Counties.
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 Jul 17, 12:43 PM EST, 24 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 143 PM EDT Sat Jul 17 2021 .SYNOPSIS... Low pressure over northern Ohio will move east-northeast today along a nearly stationary frontal boundary, and bring widespread showers and thunderstorms, some of which will be capable of producing localized strong wind gusts and flash flooding. Drier air should push south into the northern part of the Commonwealth on Sunday, though scattered to numerous showers are likely to persist during the morning hours across the Lower Susquehanna Valley. A slow moving upper trough is likely to linger over the area into much of next week, bringing overall drier conditions and a reprieve from excessive humidity. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A nearly stationary frontal boundary stretching from the I-90 corridor in Central NY to Lake Erie and Northern Ohio will be the pathway for a few waves of low pressure to move northeast along. The most organized areas of low pressure will be located across NW PA and the Central Susq Valley early this evening. Numerous showers and thunderstorms, some containing torrential rain and gusty wind will expand across the northern half of PA cover a fairly large percentage of the CWA this afternoon. SPC has upgraded the prev TSTM risk to SLGT across much of the eastern half of PA while WPC paints a slight risk of ERO over most of the CWA (Except for the far West) with a MDT risk over the NE corner of the CWA. Precipitable water values around 2 inches will mean another day of potential flash flooding from training TSRA that could easily dump 2-3 inches within less than an hour (similar to Friday across portions of the Middle Susq Valley and North- Central Mtns. A Flash Flood Watch remains in effect across our Northern Mtns and portions of our eastern CWA, where low FFG values and the potential for locally very heavy rain remain the greatest. Apparent Temps will once again tickle the 100F mark in some locations for an hour or two this afternoon across primarily Lancaster and York counties. However, right around the time of the short peak in heat indices, we should see the cooling effects of TSRA begin, thanks to SREF Capes reaching around 2000 j/kg. Slow moving front across northern PA and sfc low consolidating near KBFD this evening will keep showers and scattered very heavy rain producing TSRA going with the threat for Flash Flooding until late evening (Per the Flash Flood Watch expiration time at 02Z Sunday). && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... After an evening maximum in intensity and coverage of showers/TSRA, the SFC low moves NE and pushes its trailing cold front southeast across the region and south of the Mason Dixon line by early Sunday. Showers linger into Sunday morning behind the frontal passage across the SE half of the state, but the heavy rain threat should be over by then. Low temps early Sunday will be more refreshing in the upper 50s to lower 60s across the Northern Mtns. However, readings will stay rather muggy, only dipping into the mid 60s and lower 70s in the Central and SE zones. After a rather extensive and thick layer of post cold frontal strato cu, cloud base swill gradually lift and break up a bit in the afternoon with sfc dewpoints becoming more comfortable in the upper 50s (North and West) to low and mid 60s (Susq Valley). && .LONG TERM /MONDAY THROUGH SATURDAY/... Persistent upper level troughing with a mean west-northwest flow aloft will bring a series of cold fronts through central PA next week. Timing of these fronts is uncertain with max POPs weighted toward the afternoon and evening hours. Each front will be accompanied by scattered showers and t-storms, confined more to the NW half of CWA, but with much lower PWATs (available deep moisture) we expect the probability of heavy rainfall to remain low. CPC outlooks tilt the odds toward below average rainfall and below normal temperatures beyond midweek. SPC has noted that the overall speed of the flow aloft associated with the broad upper troughing is fcst to remain rather weak. The weak flow combined with lack of well- defined shortwave troughs and differences with frontal timing favors a low predictability for severe weather. Lastly, we were keen to utilize a 50/50 weighting of NBM with the consensus multi-model blend which trends daytime temps closer to or just below seasonal averages through midweek. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Low vis and cigs likely overnight with FG and BR at IPT and BFD, with patchy fog possible elsewhere. More showers and storms expected tomorrow with restrictions in +TSRA. Outlook... Sat...Restrictions in SHRA/TSRA Sun...Showers gradually sag southeast, reductions possible. Mon-WED...Isolated to scattered P.M. showers/t-storms. && .CTP WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch until 10 PM EDT this evening for PAZ004>006- 010>012-037-041-042-045-046-051>053-058. && SYNOPSIS...Guseman/Lambert NEAR TERM...Guseman/Lambert SHORT TERM...Guseman/Lambert LONG TERM...Guseman/Steinbugl/RXR AVIATION...Gartner/Wagner
Hazardous Weather Outlook National Weather Service State College PA 118 PM EDT Sat Jul 17 2021 PAZ004-005-010-181730- Warren-McKean-Elk- 118 PM EDT Sat Jul 17 2021 ...FLASH FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This afternoon and tonight. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Flash Flood Watch. .DAYS TWO THROUGH SEVEN...Sunday through Friday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ017>019-024>028-033>036-049-050-056-057-059-063>066-181730- Clearfield-Northern Centre-Southern Centre-Cambria-Blair-Huntingdon- Mifflin-Juniata-Somerset-Bedford-Fulton-Franklin-Union-Snyder-Perry- Dauphin-Lebanon-Cumberland-Adams-York-Lancaster- 118 PM EDT Sat Jul 17 2021 ...SEVERE THUNDERSTORM WATCH 382 IN EFFECT UNTIL 11 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This afternoon and tonight. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Severe Thunderstorm Watch. .DAYS TWO THROUGH SEVEN...Sunday through Friday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ006-011-012-037-041-042-045-046-051>053-058-181730- Potter-Cameron-Northern Clinton-Tioga-Northern Lycoming-Sullivan- Southern Clinton-Southern Lycoming-Montour-Northumberland-Columbia- Schuylkill- 118 PM EDT Sat Jul 17 2021 ...FLASH FLOOD WATCH IN EFFECT UNTIL 10 PM EDT THIS EVENING... ...SEVERE THUNDERSTORM WATCH 382 IN EFFECT UNTIL 11 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...This afternoon and tonight. Please listen to NOAA Weather Radio or go to weather.gov/StateCollege on the internet for more information about the following hazards. Flash Flood Watch. Severe Thunderstorm Watch. .DAYS TWO THROUGH SEVEN...Sunday through Friday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather.
Special Weather Statement
National Weather Service State College PA
1023 AM EDT Sat Jul 17 2021
PAZ004-005-171500-
McKean PA-Warren PA-
1023 AM EDT Sat Jul 17 2021
...A STRONG THUNDERSTORM WILL AFFECT PARTS OF MCKEAN AND WARREN
COUNTIES UNTIL 1100 AM EDT...
At 1022 AM EDT, Doppler radar indicated a strong thunderstorm near
Sheffield, moving northeast at 55 mph.
Wind gusts up to 50 mph are possible.
Locations impacted include...
Sheffield, Wetmore, Ludlow, Marshburg, Westline, Kinzua Dam and
Bradford Airport.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4178 7860 4162 7901 4163 7919 4168 7922
4199 7880
TIME...MOT...LOC 1422Z 231DEG 48KT 4170 7910
EvanegoSpecial Weather Statement National Weather Service State College PA 1235 PM EDT Sat Jul 17 2021 PAZ005-006-171715- McKean PA-Potter PA- 1235 PM EDT Sat Jul 17 2021 ...A STRONG THUNDERSTORM WILL AFFECT PARTS OF MCKEAN AND POTTER COUNTIES UNTIL 115 PM EDT... At 1235 PM EDT, Doppler radar indicated a strong thunderstorm over Crosby, moving northeast at 30 mph. Pea size hail and wind gusts up to 50 mph are possible. Locations impacted include... Coudersport, Port Allegany, Smethport, Roulette, Crosby and Oswayo. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. This storm may intensify, so be certain to monitor local radio stations and available television stations for additional information and possible warnings from the National Weather Service. && LAT...LON 4178 7786 4169 7842 4180 7848 4199 7809 TIME...MOT...LOC 1635Z 239DEG 28KT 4174 7839 Evanego
Special Weather Statement National Weather Service State College PA 123 PM EDT Sat Jul 17 2021 PAZ012-171800- Northern Clinton PA- 123 PM EDT Sat Jul 17 2021 ...A STRONG THUNDERSTORM WILL AFFECT PARTS OF NORTHERN CLINTON COUNTY UNTIL 200 PM EDT... At 123 PM EDT, Doppler radar indicated a strong thunderstorm over Westport, moving northeast at 25 mph. Pea size hail and wind gusts up to 50 mph are possible. Locations impacted include... Renovo, South Renovo, Westport and Hyner. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 4133 7755 4122 7787 4130 7792 4148 7768 TIME...MOT...LOC 1723Z 229DEG 24KT 4128 7785 Evanego
Special Weather Statement National Weather Service State College PA 133 PM EDT Sat Jul 17 2021 PAZ065-066-171800- Lancaster PA-York PA- 133 PM EDT Sat Jul 17 2021 ...A STRONG THUNDERSTORM WILL AFFECT PARTS OF LANCASTER AND YORK COUNTIES UNTIL 200 PM EDT... At 133 PM EDT, Doppler radar indicated a strong thunderstorm over Marietta, moving northeast at 15 mph. Penny size hail and wind gusts up to 50 mph are possible. Locations impacted include... Lancaster, Columbia, Millersville, Mount Joy, Manheim, East Petersburg, Stonybrook-Wilshire, Salunga-Landisville, Maytown, Mountville, Hallam, Marietta, Wrightsville, Yorklyn, Rheems, Washington Boro and Franklin And Marshall College. PRECAUTIONARY/PREPAREDNESS ACTIONS... Torrential rainfall is also occurring with this storm, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 4005 7666 4023 7641 4001 7624 3999 7664 TIME...MOT...LOC 1733Z 242DEG 13KT 4005 7656 Evanego
The Sterling radar (KLWX), 145 km away, was scanning. The volume nearest the first event began at 18:06 UTC.
23 thunderstorm wind, 4 flash flood, 2 hail. Local standard time, as filed.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires in Manor Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near Millersville.
A severe thunderstorm produced quarter-sized hail in Bird-in-Hand.
Flash flooding of several roads in the Port Allegheny area. A building collapse was also reported from a wash out.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees on wires in Jackson Township north of Myerstown.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees on Moyers Station Road near Friedensburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees across Lumber City Road, blocking both lanes.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees near Grampian.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in Paradise.
Flash flooding brought water over several roadways. In Roseville, Roseville Avenue to Dewalt Road was closed.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in multiple locations west of Lewistown.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees onto wires east of Burnham.
A severe thunderstorm producing winds estimated near 60 mph damaged trees near Shumans.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees onto Monument-Orviston Road in Liberty Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees onto Bellefonte Avenue in Lock Haven.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees onto Brewery Hollow Road west of Dunnstown.
A severe thunderstorm producing winds estimated near 60 mph knocked down a tree onto a home in Milton.
A severe thunderstorm producing winds estimated near 60 mph blew a portion of a barn roof off on North Ridge Road east of Milton.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees along Watts Drive to the south of Duncannon.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires in Kulpmont.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in multiple locations between Carroll Valley and Fairfield.
A severe thunderstorm produced half dollar sized hail northwest of Marysville.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees near the intersection of Route 42 and Wintersteen School Road.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees onto Route 118.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires and uprooted some trees east of Milton.
A severe thunderstorm producing winds estimated near 60 mph knocked down a large tree onto the right lane of Route 11 near Cherry Road.
Flash flooding resulted in water over multiple roads in Millersburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees onto Devonshire Heights Road in West Hanover Township.
Flash flooding brought water and trees across the intersection of State Route 249 and Hollenbaugh Road.
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, July 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: 966317, 966318, 965888, 971594, 966322, 966327, 966320, 966321, 966323, 971595, 966326, 966325, 966341, 966330, 966331, 966329, 966352, 966350, 967135, 966334, 966337, 965890, 966345, 966343, 966332, 966339, 971597, 966349, 971598.