A line of pre-frontal convection developed well ahead of an approaching cold front in a moderate CAPE and moderate shear environment over central Pennsylvania during the afternoon of August 4, 2017. This line of storms produced numerous reports of wind damage, and a brief EF1 tornado formed with a cell on the southern portion of this line in Fulton County, PA.
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 line of pre-frontal convection developed well ahead of an approaching cold front in a moderate CAPE and moderate shear environment over central Pennsylvania during the afternoon of August 4, 2017. This line of storms produced numerous reports of wind damage, and a brief EF1 tornado formed with a cell on the southern portion of this line in Fulton County, PA. Heavy rainfall also accompanied the storms. Flash flooding occurred across Cumberland County on the evening of the 4th.
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 Aug 4, 10:05 AM EST, 2 hours 25 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 1105 AM EDT Fri Aug 4 2017 .SYNOPSIS... Warm and more humid conditions will prevail for the rest of today until a strong cold front pushes east through the region tonight, bringing cooler and drier conditions for the weekend. Unseasonably cool weather will continue into early next week. && .NEAR TERM /UNTIL 8 PM THIS EVENING/... Airmass becoming primed for the development of scattered to numerous showers and some strong to severe TSRA from 17Z through 02Z Sat along and in advance of a strong cold front...currently near the Indiana/Ohio border. SPC's Slight Risk for severe TSRA covers all but our far eastern zones where a marginal risk is in effect. Primary, initial concern for SVR TSRA should be across the Susq Valley and Northcentral Mountains where the best combination of high cape and moderately stg llvl shear will produce 0-1 km EHIs of 1-2 m2/s2. These values of EHI will support some isolated supercells with a chc for an isolated EF0/EF1 tornado. Little change made to pops and temps for this afternoon. && .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SATURDAY/... Storms may persist after dark (00-06z Sat) given degree of large-scale ascent with vigorous upper level system and seasonably strong surface cold front. A blend of WPC/NBM QPF depicts a zone of 0.50-1.00 inch rainfall amounts along/ahead of cold FROPA ending 06z Sat. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Models are in good agreement with an unseasonably strong cold front on the doorstep of western PA by late Friday afternoon. They also agree in generating impressive instability with the added ingredient of increasing deep layer shear later in the day. The area is outlooked for a SLIGHT risk of severe storms, and at first glance it looks like the main cold front will be entering the region after max heating with waning instability. But the guidance is hinting at a pre-frontal trough developing over west-central PA which is used to act as a focus for developing convection during the afternoon. Additionally, the GFS/ECMWF paint a relatively broad area of enhanced low level EHI's by afternoon and evening which should support scattered supercells and even an isolated tornado. So anticipate scattered convection to kick off in the early afternoon with the main show later in the day through the evening. Following the cold front, Saturday will turn significantly cooler with just the chance of a few showers/thunderstorms as the still strong mid summer sun and relatively cold air aloft combine to support steepening lapse rates with daytime heating. With the upper shortwave expected to begin shearing out to our north, models suggest the best chance for a shower will be over the higher elevations of the west and north. Sunday will be dry and unseasonably cool as high pressure slides over the state. The cooler than normal conditions look to continue for much of next week. A new shortwave is made to approach for Monday. The ECMWF shows a stronger trough and even a well developed surface low racing through the state during the day. The GEFS shows a weaker inverted surface trough and a much flatter wave aloft. The ECENS agrees with its deterministic counterpart showing a well organized surface low. A model blend for POPs yields a fairly wet day as the new surge of showers pushes through the area during the day. Drier air is slated to return for midweek as the frontal system is moved off to our east. From Wed-Thu there is some disagreement with rainfall potential. The GFS/GEFS are wetter under a flatter upper zonal flow regime while the ECMWF keeps us mainly dry until the end of the week. Too early to tease out the details at this time. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... Daytime heating should pop convection around the entire area in the aftn, but the more certain timing for TSRA will be late in the aftn and through the entire evening. This will be due to the passage of a cold front. The front will drag along and ts/shra will likely linger near/over the eastern terminals through much of the night. Will knock the mentions of thunder out after 04Z west and 09Z east. .OUTLOOK... Sat-Sun...No sig wx. Mon...Showers likely, chance of thunderstorms. Tue...Chance of showers. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && SYNOPSIS...Lambert/Gartner NEAR TERM...Lambert SHORT TERM...La Corte/Steinbugl LONG TERM...La Corte/Steinbugl AVIATION...Dangelo/Lambert
Hazardous Weather Outlook National Weather Service State College PA 434 AM EDT Fri Aug 4 2017 PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-049>053- 056>059-063>066-050845- 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- 434 AM EDT Fri Aug 4 2017 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and Tonight. Severe thunderstorms with damaging winds 60 mph or greater and large hail exceeding 1 inch in diameter are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. BG/MD
Special Weather Statement
National Weather Service State College PA
851 AM EDT FRI AUG 4 2017
PAZ005-041400-
McKean PA-
851 AM EDT FRI AUG 4 2017
...A STRONG THUNDERSTORM WILL AFFECT PARTS OF MCKEAN COUNTY UNTIL
1000 AM EDT...
At 850 AM EDT, Doppler radar indicated a strong thunderstorm over
Westline, moving northeast at 20 mph.
Pea size hail and brief wind gusts in excess of 40 mph are possible.
This strong thunderstorm will be near...
Marshburg around 900 AM EDT.
Cyclone around 915 AM EDT.
Bradford and Rew around 935 AM EDT.
Other locations impacted by this storm include Eldred, Lewis Run,
University Of Pittsburgh - Bradford and Bradford Airport.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
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.
Persons in campgrounds should consider seeking sturdy shelter until
this storm passes.
&&
LAT...LON 4198 7828 4173 7876 4181 7888 4200 7869
4200 7831
TIME...MOT...LOC 1250Z 225DEG 16KT 4180 7877
LambertSpecial Weather Statement
National Weather Service State College PA
103 PM EDT FRI AUG 4 2017
PAZ056-063-064-041745-
Perry PA-Adams PA-Cumberland PA-
103 PM EDT FRI AUG 4 2017
...STRONG THUNDERSTORMS WILL AFFECT PARTS OF ADAMS...CUMBERLAND...AND
PERRY COUNTIES UNTIL 145 PM EDT...
At 102 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from near Schlusser to near Mount Holly Springs to
Cashtown. Movement was north at 15 mph.
Pea size hail and winds in excess of 40 mph are possible.
Locations impacted include...
Mechanicsburg, Carlisle, Enola, Gettysburg, Camp Hill, Plainfield,
Hogestown, Pine Grove Furnace, New Bloomfield, Mount Holly Springs,
Newville, Bloserville, Duncannon, Wertzville, Boiling Springs, Walnut
Bottom, New Kingstown, Marysville, Schlusser and Carlisle Springs.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3980 7743 3996 7747 3998 7746 4000 7748
4041 7730 4052 7698 4047 7695 4042 7702
4038 7703 4036 7700 4035 7693 4032 7691
4028 7692 4015 7700 4015 7703 4007 7714
4003 7707 3985 7718
TIME...MOT...LOC 1702Z 200DEG 13KT 4024 7713 4012 7728 3988 7736
RXRSpecial Weather Statement
National Weather Service State College PA
119 PM EDT FRI AUG 4 2017
PAZ025-034-041745-
Bedford PA-Blair PA-
119 PM EDT FRI AUG 4 2017
...A STRONG THUNDERSTORM WILL AFFECT PARTS OF BEDFORD AND BLAIR
COUNTIES UNTIL 145 PM EDT...
At 119 PM EDT, Doppler radar indicated a strong thunderstorm over
Blue Knob State Park, moving northeast at 10 mph.
Pea size hail and winds in excess of 40 mph are possible.
Locations impacted include...
Blue Knob State Park, Roaring Spring, Osterburg, Ski Gap, Queen,
Claysburg, East Freedom and Blue Knob Ski Resort.
LAT...LON 4018 7869 4021 7868 4026 7864 4028 7865
4028 7864 4031 7864 4035 7861 4037 7856
4041 7856 4033 7836 4013 7856
TIME...MOT...LOC 1719Z 214DEG 8KT 4022 7858
RXRThe State College radar (KCCX), 108 km away, was scanning. The volume nearest the first event began at 17:29 UTC.
37 thunderstorm wind, 1 flash flood. Local standard time, as filed.
A severe thunderstorm producing winds estimated near 60 mph knocked down several large trees across the 2600 block of Route 11 east of Carlisle. Trees down elsewhere in Cumberland County as well.
A severe thunderstorm producing winds estimated near 60 mph knocked down a large tree across the road near the Route 11/Route 15 split in Camp Hill.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires along Mead Run Road near Youngsville.
A severe thunderstorm producing winds estimated near 60 mph knocked down a tree and wires along Bush Hollow Road near Pennsdale.
A severe thunderstorm producing winds estimated near 60 mph knocked down a tree and wires along Jack's Hollow Road in Armstrong Township.
A severe thunderstorm producing winds estimated near 60 mph blew off a portion of a roof on a structure on West Arlington Street in Shenandoah.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in multiple locations in Colley Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees along Sugar Run Road in Allegheny Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down numerous trees and wires along Route 26 in northern Huntindgon County.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near Ogletown.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees near Bellwood.
A severe thunderstorm producing winds estimated near 60 mph knocked down wires onto Decker Hollow Road north of Tyrone.
A severe thunderstorm producing winds estimated near 60 mph knocked down several trees west of Andover.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near the intersection of Route 915 and Pleasant Valley Road near the Crystal Spring exit on I-70.
A severe thunderstorm producing winds estimated near 60 mph damaged multiple trees just east of Cowans Gap.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near McConnellsburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down a tree and wires near Upper Strasburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down multiple trees along Route 362 between Airport Road and the Wellsboro Country Club.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires near the intersection of Dantz Run Road and Route 6 west of Wellsboro.
A severe thunderstorm producing winds estimated near 60 mph snapped trees along Lake Road near Hills Creek State Park.
A severe thunderstorm producing winds estimated near 60 mph knocked down multiple trees near Dunnstown.
A severe thunderstorm producing winds estimated near 70 mph knocked down numerous trees along Route 287 near Larrysville.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees near Blain.
A severe thunderstorm producing winds estimated near 60 mph knocked down near Ickesburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees between New Bloomfield and Newport.
A severe thunderstorm produced very strong straight-line winds estimated near 90 mph, damaging a garage, a couple of barns, some trees and a cornfield north of Port Treverton in Snyder County.
A severe thunderstorm producing winds estimated near 60 mph damaged a roof on a house near Camp Hill.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees near Danville.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees along Central Road near Bloomsburg.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in Menallen Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in Huntington Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in Latimore Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires in northern Franklin County.
Numerous roads were flooded across the western portion of Cumberland County. A water rescue occurred at Clay and Hanover Streets in Carlisle.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees in Springfield Township.
A severe thunderstorm producing winds estimated near 60 mph knocked down numerous large trees near Red Lion.
A severe thunderstorm producing winds estimated near 60 mph knocked down trees and wires along New Danville Pike south of Lancaster.
A severe thunderstorm producing winds estimated near 60 mph knocked down numerous trees and wires along Ebersole Road and Ridge Avenue.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2017Every state in 2017This day in weather historyWarnings in Pennsylvania, August 2017
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: 709466, 709467, 709468, 709469, 709470, 709471, 709472, 709473, 709474, 709475, 709476, 709477, 709478, 709479, 710698, 710699, 710700, 710701, 710702, 710703, 710704, 710705, 710706, 710707, 710708, 706144, 710709, 710710, 710711, 710712, 710713, 710714, 710715, 713988, 710716, 710717, 710718, 710719.