A pattern shift occurred July 27th as high pressure propagated eastward and |was replaced by a trough that went through cyclogenesis over the Great Lakes region. Warm and moist advection increased ahead of a cold frontal passage.
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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 PBZ wrote it up.
A pattern shift occurred July 27th as high pressure propagated eastward and |was replaced by a trough that went through cyclogenesis over the Great Lakes region. Warm and moist advection increased ahead of a cold frontal passage. Diurnal heating caused the development of showers and thunderstorms by mid-afternoon. Environmental parameters were marginal in supporting a few stronger storms with gusty winds.
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 Pittsburgh, PA wrote its last area forecast discussion before the first event at Jul 27, 1:48 PM EST, 2 hours 35 minutes earlier.
Area Forecast Discussion National Weather Service Pittsburgh PA 248 PM EDT Mon Jul 27 2020 .SYNOPSIS... Showers and thunderstorms have returned for tonight and early tomorrow with a passing cold front. Slightly cooler temperature and periodic rain chance can be expected for the rest of the week. && .NEAR TERM /THROUGH TONIGHT/... Warm and moist advection is occurring ahead of a cold frontal passage. This has aided CAPE values observed by satellite to exceed 1500 j/kg. Surface based instability will aid the development of showers and thunderstorms coincident with forcing from the approach of an initial shortwave. More widespread coverage of thunderstorms is expected later this afternoon and evening when upper frontogenesis and jet divergence accompany a cold frontal passage. Isolated stronger storms may generate damaging wind gusts before sunset. This, and any hail threat will be limited by very warm temperature in the mid levels. Overall flow is sufficient for storm progression to alleviate any flood threat outside of isolated training areas. && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As the cold front propagates to the SE, some diurnal enhancement of thunderstorms along the front is expected Tuesday afternoon in West Virginia and Maryland counties. Further movement of the front south accompanied by loss of insolation should move most convection out of the region by Tuesday night. Temperature on Tuesday will be much more comfortable after cold frontal passage. && .LONG TERM /FRIDAY THROUGH MONDAY/... Seasonable temperature is expected Wednesday through much of the work week as upper troughing generally persists and provides cooler and drier air. Shortwaves within the trough accompanied by diurnal heating will provide periodic rain chances. The best chances for precipitation will be over the eastern ridges where orographic lift will boost the chance for shower development. A more widespread precipitation event is expected next weekend as models indicate a more organized sfc low pressure will lift out of the lower Mississippi River Valley toward the upper Ohio River Valley. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... VFR cumulus is expected to continue degrading this evening as scattered to numerous shra/tsra move over the region with the advn of a cdfnt. IFR restrictions are possible in heavier convection, but this wl be brief. A few showers wl also be possible later overnight with the passage of the actual front and MVFR ceilings will likely ensue thereafter. Ceilings will then rise and break up tomorrow morning and afternoon behind the frontal passage. .Outlook... Restrictions will be possible with the passage of several shortwaves through the next week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. &&
Hazardous Weather Outlook National Weather Service Pittsburgh PA 1235 PM EDT Mon Jul 27 2020 MDZ001-OHZ059-068-069-PAZ016-021>023-029-031-073>076-WVZ002>004-012- 021-509>514-281645- Garrett-Belmont-Noble-Monroe-Jefferson PA-Allegheny-Armstrong- Indiana-Washington-Greene-Westmoreland-Westmoreland Ridges-Fayette- Fayette Ridges-Brooke-Ohio-Marshall-Wetzel-Marion-Monongalia- Ridges of Eastern Monongalia and Northwestern Preston-Preston- Eastern Preston-Western Tucker-Eastern Tucker- 1235 PM EDT Mon Jul 27 2020 This Hazardous Weather Outlook is for western Maryland, east central Ohio, northwest Pennsylvania, southwest Pennsylvania, western Pennsylvania, northern West Virginia and the northern panhandle of West Virginia. .DAY ONE...This afternoon and tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to Standard Operating Procedures. OHZ039>041-048>050-057-058-PAZ007>009-013>015-020-WVZ001-281645- Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH- Muskingum-Guernsey-Mercer-Venango-Forest-Lawrence-Butler-Clarion- Beaver-Hancock- 1235 PM EDT Mon Jul 27 2020 This Hazardous Weather Outlook is for east central Ohio, northwest Pennsylvania, western Pennsylvania and northern West Virginia. .DAY ONE...This afternoon and tonight. Thunderstorms may produce damaging winds this afternoon and evening. The SPC has this area outlined in a Marginal Risk of severe weather, meaning isolated severe storms are possible. The primary threat type for this afternoon and evening is damaging wind, with a low probability of hail. Flooding is not out of the question should one area get hit with repeated bouts of convective rainfall. The WPC has outlined this area in a Marginal Risk of excessive rainfall. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Hazardous weather is not expected at this time. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to Standard Operating Procedures.
Special Weather Statement
National Weather Service Pittsburgh PA
307 PM EDT Mon Jul 27 2020
PAZ007-013-271930-
Lawrence-Mercer-
307 PM EDT Mon Jul 27 2020
...A STRONG THUNDERSTORM CAPABLE OF PRODUCING GUSTY WIND AND HEAVY
RAIN WILL AFFECT SOUTHERN MERCER AND NORTHEASTERN LAWRENCE
COUNTIES...
At 307 PM EDT, a strong thunderstorm was located near Hermitage,
moving southeast at 15 mph.
Wind gusts up to 45 mph are possible with this storm.
Locations impacted include...
Hermitage... Grove City...
New Wilmington... Mercer...
West Middlesex... Plain Grove Township...
Fredonia... Harlansburg...
Jackson Center... Volant...
Rose Point Park...
This includes the following highways...
Interstate 79 in Pennsylvania between mile markers 106 and 123.
Interstate 80 in Pennsylvania between mile markers 4 and 27.
Torrential rainfall also is occurring with this storm and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.
LAT...LON 4122 8000 4117 8000 4100 8016 4097 8017
4118 8045 4134 8031
TIME...MOT...LOC 1907Z 303DEG 13KT 4123 8035Special Weather Statement National Weather Service Pittsburgh PA 449 PM EDT Mon Jul 27 2020 PAZ007-008-013-014-272115- Butler-Venango-Lawrence-Mercer- 449 PM EDT Mon Jul 27 2020 ...AN AREA OF STRONG THUNDERSTORMS CAPABLE OF PRODUCING GUSTY WIND AND HEAVY RAIN WILL AFFECT SOUTHEASTERN MERCER...SOUTHWESTERN VENANGO...NORTHEASTERN LAWRENCE AND NORTH CENTRAL BUTLER COUNTIES... At 448 PM EDT, strong thunderstorms were clustered 8 miles northwest of Grove City, moving east at 25 mph. Wind gusts up to 45 mph are possible with this storm. Locations impacted include... Grove City... New Wilmington... Mercer... Stoneboro... Harrisville... Polk... Plain Grove Township... Sandy Lake... Clintonville... Fredonia... Jackson Center... Barkeyville... This includes the following highways... Interstate 79 in Pennsylvania between mile markers 110 and 128. Interstate 80 in Pennsylvania between mile markers 10 and 34. Torrential rainfall also is occurring with this storm and may cause localized flooding. Do not drive your vehicle through flooded roadways. LAT...LON 4111 8033 4133 8034 4140 7989 4107 7986 TIME...MOT...LOC 2048Z 266DEG 20KT 4125 8020
The Pittsburgh radar (KPBZ), 77 km away, was scanning. The volume nearest the first event began at 21:23 UTC.
3 thunderstorm wind. Local standard time, as filed.
A local 911 Call Center reported a tree down on Sharon-Mercer Road.
A local 911 Call Center reported a few trees and power lines down in southeast New Castle, PA.
A local 911 Call Center reported a tree down.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2020Every state in 2020This day in weather historyWarnings in Pennsylvania, July 2020
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: 904063, 904064, 904065.