The passage of a warm front during the morning of July 20th provided a moist and unstable air mass. A strong, progressive upper trough tracked southeastward from the Great Lakes, with an associated cold front crossing during the evening hours.
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 PBZ wrote it up.
The passage of a warm front during the morning of July 20th provided a moist and unstable air mass. A strong, progressive upper trough tracked southeastward from the Great Lakes, with an associated cold front crossing during the evening hours. Mixed-layer CAPE of up to 2500 J/kg, strong deep shear, and steep low and mid-level lapse rates were supportive of severe weather. Widespread reports of wind damage were received, mainly to trees. Some isolated urban flash flooding also occurred in Beaver and Allegheny 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 Pittsburgh, PA wrote its last area forecast discussion before the first event at Jul 20, 5:32 PM EST, 1 hour 1 minute earlier.
Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 632 PM EDT Thu Jul 20 2023 .SYNOPSIS... Strong to severe storms are likely in the I-80 corridor tonight with the primary threat being damaging winds. Secondary threats include large hail, isolated tornadoes, and flash flooding. Wind and flooding threats will remain elevated for the rest of the region overnight, though isolated tornadoes could not be ruled out. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Current observations indicated that a MCS with a history of damaging winds is diving south across Lake Erie and will impact the region beginning at 23Z in Mercer County. Pre-frontal initiation has been limited to the lakeshore with elevated capping over our area; the primary threat going forward will be coincident with the MCS. Damaging winds are likely, and isolated tornadoes and large hail remain secondary threats. Flash flooding is possible in training storms. Storm motion has been observed at 50mph as it crosses the lake, indicating the probability of severe weather is high in the I-80 corridor. Severe probabilities remain moderate to high elsewhere. Cold pool driven acceleration is likely to nudge arrival time up by as much as an hour or two. Arrival at PIT may now be closer to around 03Z. The SPC has issued a mesoscale discussion for our area highlighting the current threats and a watch has been issued to follow it up. ..Previous Discussion.. The atmosphere will destabilize this afternoon and moderate to strong shear is anticipated. Since the last update, most clouds have cleared out to just fair weather cumulus with a few towering cumulus. The warm front has passed through the entire region embedding the area in warm, moist southwest flow. Current updraft failures in northwestern PA and northern Ohio in a pre-frontal trough and along the lake boundary are acting to eat away at the morning cap and seed a more favorable, unstable environment in the I-80 corridor into this afternoon. Storm development along the pre-frontal trough is possible, but remains low probability due to observed mid-level water vapor on GOES-16 hinting at a less favorable environment for healthy, long track storms. The main question will be dependent on whether pre-frontal initiation affects our area. Any cells, particularly right moving, ahead of the cold front will effectively utilize environmental shear to for deep mesocyclones with favorable 0-1km SRH of around 75-100. This would bring larger hail and tornado threats, particularly north of I-80, should they formulate. At this point, this remains low confidence. Confidence will increase (decrease) in the coming hours if cells fire (dont fire) in the elevated mixed layer in Ohio. At this time, our best guess is storms do fire, but remain left moving and stick to the lake-shore, affecting counties just north of our area. This will need to be monitored closely. Secondly, and higher probability, a cold front affiliated with a Great Lakes low will enter our area under a similar environment around 22Z to 00Z. The southwest propagation of this line at 40- 50mph combined with around 900-1000 J/kg of DCAPE is particularly concerning for wind threats with isolated spin up tornadoes possible embedded in the line. Severe wind and isolated tornado probabilities are highest in the I-80 corridor with an earlier arrival time and lower probability of decoupling. Severe probabilities will decrease slightly as the line pulls south and decreases in propagation speed, but concerns remain notable. An elevated mixed layer seems to suggest that storms will be able to maintain themselves well into the night, with the only question being whether or not winds penetrate the shallow surface inversion. The most likely arrival time for Franklin /New Castle is 01Z-03Z, Pittsburgh /Zanesville /Indiana is 03Z-05Z, and Morgantown /Uniontown is 05Z-07Z. A severe thunderstorm watch has been issued just upstream for now, but may be expanded depending on how details play out over the next few hours. Current thinking related to threats is reflected in an SPC enhanced risk today north of Pittsburgh, with slight and marginal risks south of Pittsburgh related to the anticipated weakening trend into the night. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/... Northwest flow behind a cold front will keep this period seasonably cool. Friday will maintain a few shower chances with lingering low level moisture in a shallow mixed layer. Higher moisture and closer proximity to lift in cyclonic flow around an occluded low will mean a slight chances of isolated showers, greatest north and east of the Pittsburgh metro. Otherwise, morning fog/stratus will give way to fair weather cumulus, decreasing in coverage throughout the day. Clouds and precipitation will drop off overnight with a loss of mixing with patchy fog possible in mostly clear skies. Highs on Saturday will remain near to slightly above average. Conditions will likely remain dry with fair weather cumulus but shallow, capped instability mean a shower or two could not be ruled out. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... The long term will be defied with a persistent upper trough gradually weakening in amplitude. All clusters agree in this; there is high confidence that near average temperature will gradually and steadily trend above average. Positioning on the southeast side of the axis will lend to occasional precipitation chances, but no sizable QPF in widespread rainfall is likely. By late next week, clusters diverge into three camps. First, one solution resolves to a building eastern ridge which would mean well above average temperatures. Second, zonal flow is possible with temperatures a few ticks above average. Third, a central/western CONUS ridge would keep temperatures more near to slightly above average locally. Any way you cut the cake, the take-home message is increased probability of above average temperatures. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... A broken line of thunderstorms, ahead of an approaching cold front, is expected to track southeast across the region this evening. Along with tempo IFR conditions, large hail and damaging wind gusts are possible with these storms. Will and tafs as needed as they approach specific airports. For now, included strong wind gusts and IFR at all sites. After the storms end later this evening, deterioration to IFR stratus is expected with low level moisture pooling along the advancing front. These ceilings should lift to MVFR as mixing begins in the morning, with a return to VFR cigs expected by the afternoon. .OUTLOOK... Other than early morning patchy river valley fog, VFR is expected through Sunday night under high pressure. Restrictions are possible again Monday through early Tuesday with a crossing cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && SYNOPSIS...Milcarek NEAR TERM...Milcarek SHORT TERM...Milcarek LONG TERM...Milcarek AVIATION...WM
Hazardous Weather Outlook National Weather Service Pittsburgh PA 1258 PM EDT Thu Jul 20 2023 OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>022-029- 031-073>075-077-078-WVZ001>004-012-211700- Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson OH- Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Forest- Lawrence-Butler-Clarion-Jefferson PA-Beaver-Allegheny-Armstrong- Washington-Greene-Westmoreland-Higher Elevations of Westmoreland- Fayette-Indiana-Higher Elevations of Indiana-Hancock-Brooke-Ohio- Marshall-Wetzel- 1258 PM EDT Thu Jul 20 2023 This Hazardous Weather Outlook is for east central Ohio, western Pennsylvania, and northern West Virginia. .DAY ONE...This afternoon and tonight. Severe storms are possible this afternoon and evening with the primary threat being damaging winds. Large hail or an isolated tornado could not be ruled out. Flash flooding remains a possibility into the evening and overnight. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. 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. PAZ076-WVZ021-509>514-211700- Higher Elevations of Fayette-Marion-Monongalia- Ridges of Eastern Monongalia and Northwestern Preston-Preston- Eastern Preston-Western Tucker-Eastern Tucker- 1258 PM EDT Thu Jul 20 2023 This Hazardous Weather Outlook is for southwest Pennsylvania and northern West Virginia. .DAY ONE...This afternoon and tonight. Severe storms are possible this afternoon and evening with the primary threat being damaging winds. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. 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. Milcarek
The Pittsburgh radar (KPBZ), 92 km away, was scanning. The volume nearest the first event began at 23:31 UTC.
31 thunderstorm wind, 10 flash flood, 1 hail. Local standard time, as filed.
Trees were reported to be down in and around Sandy Lake.
Trees were blown down in and around West Salem Township.
Trees were reported to be downed in and around Sharon.
Trees and wires were blown down.
A tree was reported to be down.
Trees were reported down on Route 322.
In Jenks Township, a tree was reported down on Job Corps Road.
Numerous trees and power lines were reported to be blown down around Grove City.
A tree was blown down, blocking the westbound lane near Country Farm Supply.
Numerous trees and power lines were downed in Pine Township.
On Greenwood Road, a tree was downed.
A tree was downed on to Route 68.
A tree reportedly fell onto a vehicle, with the occupant suffering a minor injury.
Multiple trees and power lines were reported down in the area.
Trees were blown down near Knox.
Trees were reported to be blown down in the area.
A tree was reported down near Route 322.
Multiple trees and power lines were reported down in the area.
Trees and power lines were reported down in the area.
Trees were reported down in the area.
Several trees on Main Street were blown down.
Trees and power lines were reported to be down in the area.
In Brockway, trees and power lines were reported to be down.
On the southbound lane of Route 8, a tree was reported to be down.
Trees were reported to be down in Franklin Township.
Water was reported to have entered a basement in Greenville.
A few trees were reported to be down near Aliquippa.
Multiple trees were downed on Clay Plant Road.
Multiple trees were reported to be downed on Clay Plant Road, just outside the town of Brockway.
Trees were reported to be down in the area of Ambridge.
State Route 51 in South Heights was closed due to flooding.
Multiple trees were reported down along State Route 933 between Trafford and North Huntingdon Township.
The Washington Boulevard/Butler Street area near the Pittsburgh Zoo was reported to be flooded.
Power lines were reported to be down in the area.
A foot and a half of water was reported to be on northbound State Route 51, just before Monaca Road.
A road closure due to flooding occurred at the intersection of Grove Road and Village Lane.
A flooded roadway in the area was reported to have several disabled vehicles on it, but no water rescues occurred.
The eastbound Mansfield Bridge ramp was closed due to flooding.
A vehicle was reported to be stuck in flood waters.
The intersection of Clairton Boulevard and North Lewis Run Road was flooded.
Five vehicles were reported to be stuck in flood water on the ramp to the McKeesport-Duquesne Bridge, necessitating the activation of a swift water rescue team.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2023Every state in 2023This day in weather historyWarnings in Pennsylvania, July 2023
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: 1124835, 1124836, 1124885, 1124886, 1124887, 1124888, 1124890, 1124891, 1124898, 1124899, 1124900, 1124902, 1124923, 1124924, 1124925, 1124926, 1124927, 1124929, 1124946, 1124947, 1124948, 1125314, 1125316, 1125317, 1125318, 1125319, 1125330, 1125331, 1124834, 1125334, 1125337, 1125339, 1125340, 1125342, 1125344, 1125376, 1125377, 1125379, 1125380, 1125381, and more.