On July 28th, a weak surface boundary sagged south across western Pennsylvania. Despite a fair amount of instability, weak upper support, weak shear, and the downmixing of dry air helped to inhibit overall convective coverage.
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The episode as NWS PBZ wrote it up.
On July 28th, a weak surface boundary sagged south across western Pennsylvania. Despite a fair amount of instability, weak upper support, weak shear, and the downmixing of dry air helped to inhibit overall convective coverage. Nevertheless, a couple of stronger storms were able to develop during the afternoon, creating a few instances of wind damage.
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 28, 12:56 PM EST, 1 hour 22 minutes earlier.
Area Forecast Discussion National Weather Service Pittsburgh PA 156 PM EDT Wed Jul 28 2021 .SYNOPSIS... Showers and thunderstorms are likely Thursday with the passage of a cold front. High pressure returns dry and seasonably cool conditions for the first half of the weekend. && .NEAR TERM /THROUGH TONIGHT/... Surface boundary will continue to sag south through the afternoon. Weak upper support, weak shear and the potential mixing of dry air will all be detrimental to stout updrafts. In addition, temperatures are warming aloft. All factors to that should limit widespread convection through the evening. This is noted in the HRRR with a bit more development in the other CAMs. Will maintain the low chance PoPs in the forecast with the boundary - mainly south of I-80 through the evening - but generally not expecting much beyond a storm or two with strong wind gusts. Conditions should generally remain dry with diurnal cu diminishing with the loss of heating tonight. Temperatures will run above seasonal averages. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Convective Complex that is progged to develop well upstream in WI/MN this evening will dive across the Great Lakes and approach Ohio toward morning. Most of the models indicate that this complex will weaken before reaching the forecast area but will likely bring some rain to at least a portion of the region. Lingering cloud cover from the weakening MCS may delay destabilization and convective development in advance of the approaching cold front. How quickly the upper Ohio Valley can recover will ultimately be the determining factor to the extent of a severe threat as sufficient shear will be present. Storms that do develop will bring a primary threat of damaging wind but hail and an isolated tornado will also be possible, especially given the increase in 0-3km shear/helicity through Thurs afternoon. The severe threat is highlighted by the SPC Slight Risk across the entire forecast area and is noted locally in the HWO. High PWAT values will support efficient rainfall and may pose a localized/poor drainage flooding threat. High pressure will slowly build in from the northwest on Friday with dry conditions expected through Saturday. Temperatures will run below seasonal averages under cold advection. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... Ridging will remain in place over the Rockies and the southern Plains into early next week. The main band of westerlies will generally remain just north of the CWA in this pattern, with any rain chances through the period confined to areas north of I-80. Overall, a dry pattern is anticipated. In the general troughing pattern, temperatures will remain just a bit below normal. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Generally VFR conditions are forecast through the TAF period, although there will be a few opportunities for brief, isolated restrictions. A broken cumulus has developed across the region in daytime heating. Isolated showers/storms may fire near a weak surface boundary which will slowly sink southward across the region, although warming temperatures aloft and the mixing down of dry air should limit coverage greatly. VCTS was used to handle the possible impact at terminals outside of FKL/DUJ, but confidence is not high. Any convection should end by early evening as temperatures fall below convective thresholds. A mostly quiet night is then forecast. Patchy valley fog is possible once again late, but any restrictions will be brief and isolated. A decaying convective complex is expected to approach sometime after 12Z. Its intensity and path remain somewhat in question, but rain chances will be increasing after sunrise. Used VCSH for now, pending increased confidence in future TAF issuances. VCTS was reintroduced at the end for possible convection, although again, confidence is low this far out. .Outlook... More widespread restrictions are possible later Thursday afternoon and evening, as convection associated with a cold front could become strong. More quiet VFR weather is forecast for Friday and into the weekend. Restrictions and shra/tstms are likely with a Thursday cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. &&
Hazardous Weather Outlook National Weather Service Pittsburgh PA 1012 AM EDT Wed Jul 28 2021 OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-029- 031-073>076-WVZ001>004-012-021-509>514-291415- Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH- Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Forest- Lawrence-Butler-Clarion-Jefferson PA-Beaver-Allegheny-Armstrong- Indiana-Washington-Greene-Westmoreland- Higher Elevations of Westmoreland-Fayette- Higher Elevations of Fayette-Hancock-Brooke-Ohio-Marshall-Wetzel- Marion-Monongalia- Ridges of Eastern Monongalia and Northwestern Preston-Preston- Eastern Preston-Western Tucker-Eastern Tucker- 1012 AM EDT Wed Jul 28 2021 This Hazardous Weather Outlook is for east central Ohio, western Pennsylvania, and northern West Virginia. .DAY ONE...Today and tonight. Isolated severe thunderstorms, containing damaging wind gusts, are possible this afternoon and evening. .DAYS TWO THROUGH SEVEN...Thursday through Tuesday. Scattered severe thunderstorms are possible Thursday afternoon and evening. Damaging wind gusts would be the primary threat, but large hail and a tornado or two cannot be ruled out. A fair amount of uncertainty in the severe threat exists, and depends on the evolution of upstream convection tonight and Thursday morning. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
Special Weather Statement
National Weather Service Pittsburgh PA
259 PM EDT Wed Jul 28 2021
PAZ013-014-020-281930-
Butler-Lawrence-Beaver-
259 PM EDT Wed Jul 28 2021
...A STRONG THUNDERSTORM CAPABLE OF PRODUCING GUSTY WIND WILL AFFECT
NORTHEASTERN BEAVER...SOUTHWESTERN LAWRENCE AND WEST CENTRAL BUTLER
COUNTIES...
At 259 PM EDT, a strong thunderstorm was located near Oakwood, or
near New Castle, moving southeast at 20 mph.
Wind gusts up to 45 mph are possible with this storm.
Locations impacted include...
New Castle... Beaver Falls...
Ellwood City... New Brighton...
Zelienople... Oakwood...
New Castle Northwest... Patterson Township...
Big Beaver... New Beaver...
West Mayfield... Ellport...
This includes the following highways...
Pennsylvania Turnpike between mile markers 5 and 20.
Interstate 79 in Pennsylvania between mile markers 86 and 89, and
between mile markers 92 and 97.
Interstate 376 in Pennsylvania between mile markers 11 and 14.
This storm may intensify, so monitor local radio or television
stations for additional information and possible warnings from the
National Weather Service.
LAT...LON 4090 8009 4077 8012 4074 8032 4098 8052
4100 8052 4107 8041
TIME...MOT...LOC 1859Z 313DEG 19KT 4098 8043The Pittsburgh radar (KPBZ), 44 km away, was scanning. The volume nearest the first event began at 19:16 UTC.
5 thunderstorm wind. Local standard time, as filed.
At the intersection of State Route 18 and Halltown Road, the roof of a building was partially torn off, trees were blown down, and large branches were tossed around.
Multiple trees were reported down across North Beaver Township.
State Route 18 was closed due to utility lines and poles blown down across the roadway.
Power lines were blown down along Strong Road in Black Lick Township.
Utility lines were blown down along Ping Ridge Road in Burrell Township.
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: 973042, 973043, 973044, 973045, 973046.