A mesoscale convective vortex (MCV) traversed central Pennsylvania during the late afternoon of July 13, 2017, generating showers and thunderstorms. One of these storms developed into a long-lived supercell that eventually produced wind damage in southwestern Snyder County.
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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 mesoscale convective vortex (MCV) traversed central Pennsylvania during the late afternoon of July 13, 2017, generating showers and thunderstorms. One of these storms developed into a long-lived supercell that eventually produced wind damage in southwestern Snyder 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 Jul 13, 6:58 AM EST, 6 hours 48 minutes earlier.
Area Forecast Discussion National Weather Service State College PA 758 AM EDT Thu Jul 13 2017 .SYNOPSIS... Another few in a series of generally weak disturbances aloft will interact with the very warm and humid airmass in place across Pennsylvania to bring some afternoon showers and scattered thunderstorms today and Friday. The greatest chance for seeing a thunderstorm today will be across the Northern half of the state, while the threat for the most numerous showers and scattered strong to severe thunderstorms will shift to the southeast half of Pennsylvania Friday afternoon, as low pressure moving across Southern New York state pushes a cold front southeast through Pennsylvania. Following this passage of this low pressure center, mainly dry and slightly cooler weather will arrive for the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Tranquil, but rather muggy conditions were noted across all of Central Pennsylvania, the Alleghenies, and Susq Valley early today with a few showers and isolated TSRA sliding east across scent New York in the vicinity of a stalled out frontal boundary. To our west, and similar to the last few mornings, one or more MCSs area heading east toward our region, but should greatly weaken by late this morning as they lose the stronger relative inflow of moist air that's common with the decoupled blyr at this early hour of the day. Consensus of model guidance favors convection overspreading (and staying focused across) roughly the northwest half of the state late this morning through this afternoon, while mid-level temps several deg warmer (and AOA 9C) across southern PA should cap off most of the stronger, and more numerous areas convection. The convective activity breaks up/moves east of the region early this evening and becomes quite isolated in the form of mainly showers before midnight tonight. Patchy fog and isolated showers will occur late tonight. SPC continues the Marginal Risk for a few svr TSRA for the entire CWA today, as the moderately high cape combines with an area of 30-40 kt westerly winds (present from around 4kft agl up), to bring the chance for some stg to svr multicell storms and mini bow echoes - with a few instances of isolated wind damage possible. The other forecast issue today (and possibly Friday as well) is the potential for locally heavy rainfall within a quasi, east/west ribbon of high PWAT air across mainly northern and western PA this afternoon and evening. Even though WPC's Day 1 excessive rainfall is in the Slight Risk category over roughly the western half of our CWA, our forecast NDFD QPF is still well below 1-6 hourly FFG, and the convection location will be widely varying/and likely staying transient without the presence of a good mesoscale/synoptic frontal boundary over our region. Again the NW mtns (and perhaps Wcent PA) should see the greatest threat for Flash Flooding and training TSRA given the cooler temps aloft and closer proximity to the boundary across southern/central New York State. Temps will start out in the U60s to L70s this morning, and reach highs in the lower 80s across the nrn and wrn mtns, and mid 80s to lower 90s respectively acrs the central and SE part of the CWA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... The initial pair of short waves that supported the Ohio Valley and Central/Western Great Lakes MCSs early Thursday will drift east of the Susq Valley shortly before dusk this evening...likely followed by another mainly dry night with partly to mostly cloudy skies, light wind and patchy 1/2-1SM fog in places that receive rain today and see some periods partial clearing tonight. low temps tonight will vary from the 60s across the mountains of the north and west, to between 70-75F throughout the central and southern valleys of our CWA. Main sfc-850 mb quasi-stnry frontal boundary will stay to the the north of our area through the morning hours Friday, before sinking slowly south as a wave of low pressure moves east across southern New York. A period of heat indices in the low to mid 90s will occur Friday across our SE zones, but I don't expect that they'll be quite high enough to post and Excessive Heat Watch (today) or Heat Advisory (either tonight or Friday). Model and ensemble guidance remains in good agreement this period with gradual/modest amplification of the Eastern U.S. trough in response to strengthening upper level ridge centered over the Four Corners states. Well organized and moderately strong shortwave energy traversing the area, in conjunction with attendant low pressure wave/front will support maximum large scale lift (beneath the RE region of a 75KT upper level jet) and pcpn potential Friday-early Friday night. Widespread mid-upr level debris cloudiness tomorrow could limit the daytime heating. The main area of concern for Severe TSRA Friday afternoon/evening will be near and to the SE of Interstate 81, where SPC has a Day 2 Slight Risk area painted. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... High pressure is forecast to dominate the region on Saturday with an expected break from pcpn and hier humidities of this week. However, a trailing front progressing from southern Canada may generate some convection on Sunday before moving off the coast early next week. High pressure should bring dry wx and less humid air again Monday. However, returning moisture behind the stalling front will bring an increasing chance for showers on Tuesday and Wednesday. Temperatures should be within a few degrees of mid- July climate normals. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... VFR will be the primary category this morning. An approaching complex will bring isolated showers and storms impacting portions of the area mainly between Route 6 and I-80 with the only current storms will be in the vicinity of BFD by 14Z. Otherwise scattered showers will track to the western TAF sites late this morning, early this afternoon. Have adjusted and or removed the TEMPO groups based on timing confidence and concerns of near term models. Restrictions spread in from the NW late tonight/early Friday along with development of a line of showers/thunderstorms that will bring about a 3hr window for storms as they work southeastward. Convection will become more scattered as it approaches the Lower Susq Valley later in the day. .OUTLOOK... Fri...Mainly VFR with localized sub-VFR in thunderstorms. Sat...Improving conditions. Sun...No sig wx. Mon...Sct TSRA. Local restrictions. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Gartner AVIATION...Ceru/RXR
Hazardous Weather Outlook National Weather Service State College PA 445 AM EDT Thu Jul 13 2017 PAZ005-006-010>012-017>019-024-037-041-042-045-046-049>053-140845- McKean-Potter-Elk-Cameron-Northern Clinton-Clearfield- Northern Centre-Southern Centre-Cambria-Tioga-Northern Lycoming- Sullivan-Southern Clinton-Southern Lycoming-Union-Snyder-Montour- Northumberland-Columbia- 445 AM EDT Thu Jul 13 2017 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and Tonight. Isolated strong to severe thunderstorms with gusty winds and hail are possible during the afternoon and evening hours today. Locally heavy rain of over one inch in just 30 minutes is possible from training showers and thunderstorms. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Scattered strong to severe thunderstorms with gusty winds and hail are possible once again Friday afternoon and evening. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ025>028-033>036-056>059-063>066-140845- Blair-Huntingdon-Mifflin-Juniata-Somerset-Bedford-Fulton-Franklin- Perry-Dauphin-Schuylkill-Lebanon-Cumberland-Adams-York-Lancaster- 445 AM EDT Thu Jul 13 2017 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and Tonight. Isolated strong to severe thunderstorms with gusty winds and hail are possible during the afternoon and evening. In addition, dangerous heat conditions are possible this afternoon across the Lower Susquehanna Valley where maximum heat index values near 100 degrees. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Severe thunderstorms with damaging winds 60 mph or greater and large hail exceeding 1 inch in diameter are possible Friday afternoon and evening. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather. PAZ004-140845- Warren- 445 AM EDT Thu Jul 13 2017 This Hazardous Weather Outlook is for central Pennsylvania. .DAY ONE...Today and Tonight. Isolated strong to severe thunderstorms with gusty winds and hail are possible during the afternoon and evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Scattered strong to severe thunderstorms with gusty winds and hail are possible Friday afternoon. .SPOTTER INFORMATION STATEMENT... Spotters are encouraged to report significant hazardous weather.
Special Weather Statement
National Weather Service State College PA
203 PM EDT THU JUL 13 2017
PAZ019-027-131830-
Mifflin PA-Southern Centre PA-
203 PM EDT THU JUL 13 2017
...A STRONG THUNDERSTORM WILL AFFECT PARTS OF MIFFLIN AND SOUTHERN
CENTRE COUNTIES UNTIL 230 PM EDT...
At 202 PM EDT, Doppler radar indicated a strong thunderstorm over
Boalsburg, moving east at 30 mph.
Wind gusts of 40 to 50 mph are possible.
Locations impacted include...
Potters Mills, Milroy, Seven Mountains, Poe Valley State Park, Reeds
Gap State Park, Centre Hall, and Reedsville.
LAT...LON 4067 7769 4068 7768 4069 7771 4072 7768
4073 7768 4079 7781 4084 7778 4084 7736
4074 7736 4067 7754
TIME...MOT...LOC 1802Z 289DEG 25KT 4080 7773
DangeloThe State College radar (KCCX), 65 km away, was scanning. The volume nearest the first event began at 18:46 UTC.
1 thunderstorm wind. Local standard time, as filed.
A severe thunderstorm producing winds estimated near 60 mph knocked down and snapped trees along Ridge Road between McClure and Beaver Springs.
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, July 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: 700050.