Slow moving thunderstorms produced flash flooding mainly across Pittsburgh and Allegheny county.
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.
Slow moving thunderstorms produced flash flooding mainly across Pittsburgh and Allegheny 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 Pittsburgh, PA wrote its last area forecast discussion before the first event at Jul 20, 12:59 PM EST, 6 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
159 PM EDT FRI JUL 20 2012
.SYNOPSIS...
A SLOW MOVING UPPER LOW PRESSURE SYSTEM WILL PROVIDE SHOWERS AND
POSSIBLY A THUNDERSTORM THROUGH TONIGHT. SOME RAIN WILL BE HEAVY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
THE FRONT CONTINUES TO TRUDGE ACROSS THE FORECAST AREA EARLY THIS
AFTERNOON...NOW RUNNING BASICALLY FROM INDIANA...THROUGH THE
PITTSBURGH AREA...TO JUST SOUTH OF ZANESVILLE. CONVECTION IS
FIRING ALONG AND AHEAD OF THIS FRONT AS OF 1230...AND IT WOULD
SEEM THIS TREND SHOULD INCREASE IN THE NEXT COUPLE OF HOURS. GIVEN
THE WEAK SHEAR AND SLOW-MOVING NATURE OF THE FRONT...AND OF THESE
CELLS IS CAPABLE OF PRODUCING LOCALLY HEAVY RAINFALL. A FLASH
FLOOD WATCH HAS BEEN ISSUED UNTIL 8 PM TONIGHT TO COVER THE
LOCALLY HEAVY RAINFALL THREAT.
OUTSIDE OF RAINFALL...DENSE CLOUD COVER CONTINUES TO COVER THE
AREA. DIURNAL TEMPERATURE RISES HAVE BEEN BASICALLY NIL THROUGH
THE MORNING HOURS...AND GIVEN LITTLE/NO TREND TOWARD ANY BREAKUP
OF THE LOW CLOUD COVER...HIGH TEMPERATURES WERE CUT BACK AGAIN.
TEMPERATURES FOR MOST AREA SHOULD STAY NEARLY STEADY THROUGH THE
AFTERNOON BEFORE FALLING BACK TONIGHT. FRIES
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
THE ENTIRE UL SYSTEM SLOWLY MOVES EASTWARD TONIGHT, WHICH WILL
ALSO PUSH THE SFC FRONT FURTHER SOUTH. SHOWERS WILL WIND DOWN OVER
THE EASTERN HALF AND SHOULD END IN THE RIDGES EARLY SAT MORNING.
MODELS ARE INDICATING THAT THERE WILL STILL BE PLENTY OF CLOUDS
LEFT OVER ON SAT, AT LEAST THROUGH THE FIRST HALF OF THE DAY, AS
THE MID AND LL FLOW IS EASTERLY. THERE WILL BE A BIG DIFFERENCE IN
TEMPS FROM WEST TO EAST AS THE WEST WILL GET RID OF THE CLOUD
COVER SOONER. HUMIDITY LEVELS WILL START TO CREEP BACK UP ON SAT.
ANOTHER SW TROUGH WILL MOVE THROUGH SUNDAY NIGHT. AT THIS POINT IT
DOES NOT APPEAR THERE WILL BE ANY PRECIP WITH THE SYSTEM, AS THE
MAIN WAVE STAYS TO THE WEST. HOWEVER THIS WILL BRING CLOUDS BACK
INTO THE AREA SAT NIGHT.
DIFFERING MODEL SOLUTIONS ON SUNDAY AS THE NAM WANTS TO KEEP THE
TROUGH OVER THE AREA WHILE THE GFS LIFTS IT TO THE EAST. THE 12Z
ECMWF IS IN PRETTY GOOD AGREEMENT WITH THE 00Z GFS, SO WILL KEEP
THE FORECAST DRY.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A COLD FRONT IS PROJECTED TO PUSH ACROSS THE UPPER OHIO REGION ON
MONDAY INTO TUESDAY BRINGING SHOWERS AND SCATTERED THUNDERSTORMS.
HIGH PRESSURE SHOULD THEN BRING DRY WEATHER FOR WEDNESDAY INTO
THURSDAY. SOME SHOWERS ARE POSSIBLE LATE THURSDAY AHEAD OF THE
NEXT COLD FRONT.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
RECENT SURFACE AND SATELLITE DATA SHOW AREAS OF IFR STRATUS AND
PATCHY MVFR FOG ACROSS THE UPPER OHIO VALLEY, AS A SURFACE LOW
PRESSURE CENTER MOVES SLOWLY SOUTHEASTWARD THROUGH THE REGION.
HAVE ADDED SHOWERS AND A SHORT-PERIOD OF THUNDERSTORMS FOR KPIT
KAGC AND KLBE. AS AN EAST-WEST BAND OF SHOWERS AND ISOLATED
THUNDERSTORMS MOVES EASTWARD PAST THESE TAF SITES THROUGH 13Z.
CONCUR WITH RECENT GFS LAMP AND NAM MOS THAT IFR CEILING
RESTRICTIONS WILL REMAIN UNTIL ABOUT 15Z, DUE TO RECENT RAIN AND
LIKELY CONTINUED LOW LEVEL TEMPERATURE INVERSION THAT WILL CAP
SHALLOW SURFACE LAYER AND PREVENT STRATUS FROM VERTICALLY MIXING
OUT UNTIL LATE MORNING.
NORTH WINDS NEAR 10 KTS, IN THE WAKE OF THE LOW PRESSURE CENTER
PASSAGE, WILL MAINTAIN STABLE CONDITIONS THIS AFTERNOON AND TONIGHT.
SO EXPECT CEILINGS TO LIFT NO HIGHER THAN MVFR LEVELS THIS
AFTERNOON, BEFORE LOWERING BACK TO IFR LATE TONIGHT. FOG MAY THEN
ADD VISIBILITY RESTRICTIONS.
OUTLOOK...SATURDAY THROUGH TUESDAY...
AREAS OF STRATUS AND PATCHY FOG MAY RESULT IN LINGERING RESTRICTIONS
INTO SATURDAY MIDDAY. THEN EXPECT MAINLY VFR LATE SATURDAY INTO
EARLY MONDAY. SCATTERED PREFRONTAL THUNDERSTORMS MAY PROVIDE
RESTRICTIONS MONDAY INTO TUESDAY.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR MDZ001.
OH...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR OHZ059-068-
069.
PA...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR PAZ021-023-
029-031-073>076.
WV...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR WVZ002>004-
012-021>023-041.
&&HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE PITTSBURGH PA 359 AM EDT FRI JUL 20 2012 MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023- 029-031-073>076-WVZ001>004-012-021>023-041-210800- GARRETT-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-WESTMORELAND RIDGES- FAYETTE-FAYETTE RIDGES-HANCOCK-BROOKE-OHIO-MARSHALL-WETZEL-MARION- MONONGALIA-PRESTON-TUCKER- 359 AM EDT FRI JUL 20 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MARYLAND...EAST CENTRAL OHIO...NORTHWEST PENNSYLVANIA...SOUTHWEST PENNSYLVANIA...WEST CENTRAL PENNSYLVANIA...NORTHERN WEST VIRGINIA AND NORTHERN PANHANDLE OF WEST VIRGINIA. .DAY ONE...TODAY AND TONIGHT. NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY. NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
The Pittsburgh radar (KPBZ), 27 km away, was scanning. The volume nearest the first event began at 18:03 UTC.
17 flash flood. Local standard time, as filed.
Emergency management reported SR 51 near Whitehall was flooded with a vehicle floating.
Emergency management reported SR 51 at East Bruceton Road closed due to flash flooding.
Law enforcement reported Oakdale Road closed due to flash flooding.
Law enforcement reported Cliff Mine Road and Mahoney Road closed due to flash flooding.
The public reported flash flooding on roadways.
The public reported creeks out of their banks flooding roadways.
Emergency management reported creeks out of their banks and flooding streets.
Emergency management reported Coal Valley Road at Clairton Road closed due to flash flooding.
Emergency management reported flash flooding on E 5th Street.
Emergency management reported SR 51 and Brownsville Road is completely shut down by flooding.
Emergency management reported flash flooding in Dravosburg on SR 837.
Emergency management reported Worthington Ave clsoed due to flash flooding.
Emergency management reported flash flooding on Oakdale Road.
The public reported flash flooding on Campbells Run Road.
An off duty NWS employee reported a creek flooding roads with water approaching a few homes.
Law enforcement reproted flash flooding on Blind Lane Road.
An off duty NWS employee reproted water into homes and bridges flooded on McClaren Raod.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2012Every state in 2012This day in weather historyWarnings in Pennsylvania, July 2012
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: 401956, 401962, 402484, 402486, 401983, 401985, 401990, 401993, 401996, 401997, 401999, 402001, 402004, 402010, 402012, 402014, 402016.