Scattered severe thunderstorms formed well ahead of a cold front moving east across the upper Ohio Valley, with wind damage reported across eastern Ohio, western Pennsylvania, and northern West Virginia.
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.
Scattered severe thunderstorms formed well ahead of a cold front moving east across the upper Ohio Valley, with wind damage reported across eastern Ohio, western Pennsylvania, and northern West Virginia.
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 Aug 20, 2:23 PM EST, 3 hours 47 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 323 PM EDT THU AUG 20 2009 .SYNOPSIS... SHOWERS AND THUNDERSTORMS ARE EXPECTED THROUGH FRIDAY AS A SERIES OF FRONTS MOVE EASTWARD THROUGH THE HUMID AIR MASS COVERING THE UPPER OHIO VALLEY. CONDITIONS WILL TURN COOLER THIS WEEKEND. && .NEAR TERM /THROUGH FRIDAY/... RISK FOR SEVERE THUNDERSTORMS WILL REMAIN THROUGH THE EVENING HOURS. MAIN THREAT IS FOR DAMAGING WINDS...AS HIGH FREEZING LEVELS SHOULD LIMIT THE POSSIBILITY OF SEVERE CRITERIA HAIL REACHING THE GROUND. PRECIPITATION SHOULD TAPER OFF BY MIDNIGHT AFTER PREFRONTAL TROUGH WITH SHOWERS AND THUNDERSTORMS PUSHES THROUGH THE REGION. WHILE CONDITIONS MAY BE DRY DURING THE LATE NIGHT HOURS...BOTH THE GFS AND NAM SHOW AN AXIS OF HIGHER PRECIPITATION ASSOCIATED WITH A COLD FRONT IN THE 09Z-15Z TIME RANGE. WITH THE HIGH DEWPOINTS AND PRECIPITABLE WATER VALUES ALREADY IN PLACE...WOULD NOT BE SURPRISED TO SEE A LINE OF HEAVY RAIN MOVE THROUGH DURING THE MORNING HOURS. BUFKIT PROFILES SHOW STRONG WIND SHEAR ALSO OCCURRING AT THIS TIME...BUT LIMITED INSTABILITY VALUES DUE TO LOW LAPSE RATES ALOFT AND THE TIME OF DAY MAY PREVENT ANY SEVERE WEATHER FROM OCCURRING WITH THE RAIN. AFTER THE MORNING RAIN...MODELS ARE IN GENERAL AGREEMENT THAT A DRY SLOT WILL THEN PASS OVER...DRYING OUT CONDITIONS. EXPECT A REDUCED DIURNAL RANGE IN TEMPERATURES DUE TO THE EXTENSIVE CLOUD COVER. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... ONCE SURFACE LOW AND COLD FRONT DEPART...UPPER LOW WILL REMAIN OVER THE GREAT LAKES INTO SATURDAY. NAM AND ECMWF PUT OUT SMALL AMOUNTS OF PRECIPITATION...WHILE THE GFS AND SREF KEEP CONDITIONS CLOUDY BUT DRY. WILL STAY CLOSE TO THE PREVIOUS FORECAST...WHICH INCLUDES A CHANCE OF SHOWERS ON SATURDAY BEFORE THE LOW BEGINS MOVING EAST. HIGH TEMPERATURES WILL BE AROUND 5 DEGREES BELOW NORMAL WITH THE NORTHERLY FLOW. && .LONG TERM /SUNDAY THROUGH THURSDAY/... BLEND OF RECENT GEFS AND ECMWF MODEL OUTPUT SHOW THAT THE COLD UPPER TROUGH MOVING THROUGH THE UPPER OHIO VALLEY THIS WEEKEND MAY STILL PRODUCE ISOLATED INSTABILITY SHOWERS SUNDAY. HIGH PRESSURE FROM THE MIDWEST SHOULD THEN PROVIDE THE UPPER OHIO VALLEY WITH DRY COMFORTABLE CONDITIONS MONDAY AND TUESDAY. MODEL OUTPUTS THEN DIVERGE ON TIMING OF SHOWERS WITH A LOW PRESSURE SYSTEM MOVING THROUGH THE GREAT LAKES MID WEEK. DEFERRED TO HPC THINKING THAT THERE COULD BE A CHANCE OF SHOWERS AND THUNDERSTORMS WEDNESDAY AND THURSDAY. FORECASTED TEMPERATURES TO START OUT COOLER THAN NORMAL SUNDAY BUT THEN REACH SEASONABLE LEVELS THE REST OF THE PERIOD...AS INDICATED BY CONSENSUS OF HPC AND GFS MOS GUIDANCE. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... BASED ON BLEND OF RECENT RADAR DATA AND SREF...WRF- NMM...HRRR...AND GFS LAMP...CONTINUED TO FORECAST A BAND OF MORE NUMEROUS MVFR THUNDERSTORMS TO CROSS THE UPPER OHIO VALLEY BETWEEN 20Z AND 03Z. THERE CAN BE BRIEF IFR IN HEAVY THUNDERSTORM RAIN. SPC HAS CONCERNS THE STORMS HAVE SEVERE POTENTIAL DUE TO INCREASED EFFECTIVE BULK VERTICAL WIND SHEAR TO 35 KTS. HIGH WIND GUSTS THE PRIME HAZARD. SREF MODEL OUTPUT ALSO SHOWS ANOTHER BAND OF MVFR SHOWERS AND IFR THUNDERSTORMS CROSSING THE UPPER OHIO VALLEY FRIDAY MORNING. CONCUR WITH SPC THAT DUE TO TIMING OF EPISODE...THERE MAY NOT BE ENOUGH SURFACE HEATING FOR INSTABILITY TO TAP THE VERTICAL SHEAR NEEDED FOR STORMS TO REACH SEVERE THRESHOLDS. BLEND OF RECENT SREF GEFS AND ECMWF MODEL OUTPUT SHOWS SURFACE LAYER DRYING ACROSS THE UPPER OHIO VALLEY IN WAKE OF FRIDAYS COLD FRONT. SO EXPECT PREVALENT VFR SATURDAY THROUGH TUESDAY. ONLY POSSIBLE INTERRUPTIONS CAN BE ISOLATED AFTERNOON MVFR SHOWERS SATURDAY AND SUNDAY DUE TO ENSUING SLOW EASTWARD MOVING COLD UPPER TROUGH AND ISOLATED IFR FOG PATCHES EACH MORNING AS IS COMMON THIS TIME OF YEAR. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE PITTSBURGH PA 708 PM EDT THU AUG 20 2009 MDZ001-PAZ008-009-014>016-021>023-029>032-WVZ021>023-041-212315- GARRETT-VENANGO-FOREST-BUTLER-CLARION-JEFFERSON PA-ALLEGHENY- ARMSTRONG-INDIANA-WASHINGTON-WESTMORELAND-GREENE-FAYETTE-MARION- MONONGALIA-PRESTON-TUCKER- 708 PM EDT THU AUG 20 2009 ...SEVERE THUNDERSTORM WATCH 723 IN EFFECT UNTIL MIDNIGHT EDT TONIGHT... THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MARYLAND...NORTHWEST PENNSYLVANIA...SOUTHWEST PENNSYLVANIA...WEST CENTRAL PENNSYLVANIA AND NORTHERN WEST VIRGINIA. .DAY ONE...TONIGHT. PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS. SEVERE THUNDERSTORM WATCH. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY. 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>059-068-069-PAZ007-013-020-WVZ001>004-012- 212315- TUSCARAWAS-CARROLL-COLUMBIANA-COSHOCTON-HARRISON-JEFFERSON OH- MUSKINGUM-GUERNSEY-BELMONT-NOBLE-MONROE-MERCER-LAWRENCE-BEAVER- HANCOCK-BROOKE-OHIO-MARSHALL-WETZEL- 708 PM EDT THU AUG 20 2009 ...SEVERE THUNDERSTORM WATCH 721 IN EFFECT UNTIL 10 PM EDT THIS EVENING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL OHIO...NORTHWEST PENNSYLVANIA...SOUTHWEST PENNSYLVANIA...WEST CENTRAL PENNSYLVANIA...NORTHERN WEST VIRGINIA AND NORTHERN PANHANDLE OF WEST VIRGINIA. .DAY ONE...TONIGHT. PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO WEATHER.GOV ON THE INTERNET FOR MORE INFORMATION ABOUT THE FOLLOWING HAZARDS. SEVERE THUNDERSTORM WATCH. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY. 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.
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE PITTSBURGH PA 122 PM EDT THU AUG 20 2009 PAZ014-020-021-201745- ALLEGHENY PA-BEAVER PA-BUTLER PA- 122 PM EDT THU AUG 20 2009 ...THUNDERSTORMS... THUNDERSTORMS TO MOVE THROUGH THE FOLLOWING COUNTIES... ALLEGHENY...BEAVER AND BUTLER... AT 118 PM EDT NATIONAL WEATHER SERVICE DOPPLER RADAR IN PITTSBURGH INDICATED THUNDERSTORMS WITH HEAVY RAIN AND GUSTY WINDS OVER SEWICKLEY...MOVING NORTHEAST AT 25 MPH. SOME LOCATIONS THAT WILL BE IMPACTED BY THESE STORMS INCLUDE... SEWICKLEY... FRANKLIN PARK... WEXFORD... GIBSONIA... MARS... WITH THE STORM...WINDS CAN GUST OVER 30 MPH. RAIN AMOUNTS CAN GO OVER AN INCH IN LESS THAN 30 MINUTES WHICH COULD CAUSE PONDING OF WATER ON ROADS AND IN LOW LYING URBAN AREAS. AVOID THESE AREAS UNTIL AN HOUR AFTER THE RAIN SUBSIDES. WATER LEVELS OF SMALL STREAMS AND CREEKS MAY ALSO RISE. SO AVOID THESE ALSO. STAY ON HIGHER GROUND. KEEP AN EYE TO THE SKY AND MOVE TO A SAFE PLACE IF THUNDERSTORMS APPROACH. PLEASE REPORT HAIL...STRONG WINDS OR WIND DAMAGE TO THE NATIONAL WEATHER SERVICE BY CALLING TOLL FREE...1-877-633-6772. &&
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE PITTSBURGH PA 539 PM EDT THU AUG 20 2009 OHZ041-PAZ007-008-013-014-020-202245- BEAVER PA-BUTLER PA-COLUMBIANA OH-LAWRENCE PA-MERCER PA-VENANGO PA- 539 PM EDT THU AUG 20 2009 ...THUNDERSTORMS TO MOVE THROUGH THE FOLLOWING COUNTIES... COLUMBIANA...BEAVER...BUTLER...VENANGO...MERCER AND LAWRENCE... AT 538 PM EDT NATIONAL WEATHER SERVICE DOPPLER RADAR IN PITTSBURGH INDICATED STRONG THUNDERSTORMS 6 MILES SOUTHWEST OF NEW CASTLE...MOVING NORTHEAST AT 25 MPH. THESE STORMS CONTAIN VERY HEAVY DOWNPOURS AND MAY PRODUCE ONE HALF INCH HAIL AND WIND GUSTS TO 35 MPH. SOME LOCATIONS THAT WILL BE IMPACTED BY THESE STORMS INCLUDE... NEW CASTLE... NEW WILMINGTON... HARLANSBURG... SLIPPERY ROCK... GROVE CITY... KEEP AN EYE TO THE SKY AND MOVE TO A SAFE PLACE IF THUNDERSTORMS APPROACH. PLEASE REPORT HAIL...STRONG WINDS OR WIND DAMAGE TO THE NATIONAL WEATHER SERVICE BY CALLING TOLL FREE...1-877-633-6772. PRECAUTIONARY/PREPAREDNESS ACTIONS... A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 1000 PM EDT THURSDAY EVENING FOR EAST CENTRAL OHIO AND NORTHWESTERN PENNSYLVANIA AND NORTHERN WEST VIRGINIA. &&
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PITTSBURGH PA
646 PM EDT THU AUG 20 2009
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0636 PM TSTM WND DMG GROVE CITY 41.16N 80.09W
08/20/2009 MERCER PA EMERGENCY MNGR
TREES DOWN ON DIAMOND ST.
&&
ASMITHThe Pittsburgh radar (KPBZ), 121 km away, was scanning. The volume nearest the first event began at 23:10 UTC.
1 thunderstorm wind. Local standard time, as filed.
The local fire department reported power lines down in Graysville.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Ohio in 2009Every state in 2009This day in weather historyWarnings in Ohio, August 2009
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: 191677.