A stationary boundary was stalled across the region. A very moist airmass was in place with high PWAT values.
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 LWX wrote it up.
A stationary boundary was stalled across the region. A very moist airmass was in place with high PWAT values. Showers and thunderstorms that did develop caused flash flooding.
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 Baltimore/Washington wrote its last area forecast discussion before the first event at Sep 2, 8:44 AM EST, 4 hours 56 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 944 AM EDT SUN SEP 2 2012 .SYNOPSIS... A WEAK FRONTAL BOUNDARY WILL REMAIN STATIONARY ACROSS CENTRAL VIRGINIA TODAY...BUT BEGIN SHIFTING NORTHWARD DURING THE DAY ON MONDAY. THE REMNANTS OF ISAAC WILL INTERACT WITH THE FRONTAL BOUNDARY TO PRODUCE UNSETTLED CONDITIONS THROUGH AT LEAST TUESDAY. A COLD FRONTAL PASSAGE SHOULD BRING DRIER CONDITIONS BY THE END OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... WEAK FRONTAL BOUNDARY WILL REMAIN STATIONARY ACROSS CENTRAL VIRGINIA THROUGH TONIGHT. SEVERAL PIECES OF MID LEVEL SHORTWAVE ENERGY WILL MOVE ALONG THE BOUNDARY...EACH ENHANCING THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS. 12Z SOUNDING ANALYSIS SHOWS A VERY MOIST AIRMASS IN PLACE WITH PWATS AROUND 2 INCHES. THIS IS SLIGHTLY UNDER TWO STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF YEAR...HOWEVER PWATS ARE FORECAST TO INCREASE OVERNIGHT AND MONDAY TO NEAR THE TWO STANDARD DEVIATION MARK. BOUNDARY LAYER WINDS ARE 15 KT OR LESS...SO WITH THE SLOW MOVEMENT AND TRAINING OF ANY STORMS...LOCALIZED FLASH FLOODING IS POSSIBLE TODAY. IN ADDITION...AREAS THAT RECEIVE HEATING WILL HAVE THE POTENTIAL FOR BETWEEN ONE AND TWO THOUSAND JULES OF CAPE THIS AFTERNOON. MID LEVEL LAPSE RATES AND 0-6KM SHEAR ARE NOT IMPRESSIVE...BUT A FEW STORMS COULD PRODUCE DAMAGING WIND GUSTS. WET BULB ZERO/FREEZING LEVEL HEIGHTS ARE A FEW THOUSAND FEET ABOVE YESTERDAY'S VALUES...SO WIND WILL BE MORE LIKELY THAN HAIL. CURRENTLY RAINFALL IS CONFINED TO THE SHENANDOAH VALLEY AND WESTWARD...ALONG THE WEAK BOUNDARY. DO EXPECT THE AREA OF RAINFALL TO CONTINUE SPREADING SLOWLY EASTWARD TODAY...AND ORIENTING JUST ALONG THE STALLED FRONT. WILL LIKELY HAVE TO ADJUST POPS ALONG THIS AXIS AS THE PRECIP FILLS IN TO THE EAST/SOUTHEAST. 06Z MODELS DO INDICATE A BREAK FOR A FEW HOURS OVERNIGHT IN THE PRECIP...AND WILL SEE IF THE 12Z MODELS AGREE. IF THEY ARE CONSISTENT...WILL HAVE TO ADJUST POPS DOWN FOR A FEW HOURS OVERNIGHT. && .SHORT TERM /MONDAY THROUGH TUESDAY/... DEEP MOISTURE IS FORECAST TO REMAIN OVER THE AREA MONDAY/TUESDAY AS THE REMNANTS OF ISAAC SHIFT TO THE EAST. MODELS CONTINUE TO SHOW A FRONTAL BOUNDARY STALLED OUT ACROSS CENTRAL VIRGINIA...AND ISENTROPIC LIFT TO THE NORTH OF THE BOUNDARY HELPING TO SUPPORT EPISODES OF SHOWERS AND THUNDERSTORMS ACROSS THE CWA. GFS SHOWS PRECIPITABLE WATER VALUES OF 2 TO 2.25 INCHES...INDICATING THE POTENTIAL FOR HEAVY RAINFALL AND THUS FLASH FLOODING. ITS DIFFICULT TO PINPOINT THE DETAILS OF CONVECTIVE BANDS BOTH IN TERMS OF LOCATION AND TIMING...SO THERE/S STILL SOME UNCERTAINTY AS TO WHERE/WHEN THE GREATEST FLASH FLOOD THREAT WOULD EXIST AND WILL NEED TO FINE TUNE THE DETAILS AS WE GET CLOSER. HWO WILL CONTINUE TO MENTION RISK DURING THIS TIME. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... TROPICAL MOISTURE MAY LINGER INTO WEDNESDAY AS WELL...AS A FRONT AND ASSOCIATED LOW PRESSURE ARE FORECAST TO MOVE ACROSS THE AREA FOR A CHANCE OF SHOWERS AND THUNDERSTORMS. A REINFORCING FRONT ON THE HEELS OF ITS PREDECESSOR ON THURSDAY LOOKS TO PUSH THE DEEP MOISTURE PLUME TO THE EAST AND BRING DRIER AIR ACROSS THE AREA BY FRIDAY AS HIGH PRESSURE BUILDS IN. HIGH PRESSURE MAY ONLY PAY A BRIEF VISIT HOWEVER AS GFS/ECMWF SHOW RETURN FLOW COMING BACK FOR SATURDAY AND ANOTHER COLD FRONT APPROACHING FOR SUNDAY. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... A STALLED FRONTAL BOUNDARY WILL REMAIN ACROSS CENTRAL VIRGINIA THROUGH TONIGHT. PRECIPITATION WILL FOCUS ALONG THIS BOUNDARY AS SEVERAL PIECES OF MID LEVEL SHORTWAVE ENERGY MOVE SE ALONG THE STALLED FRONT. PRECIP WILL BECOME MORE WIDESPREAD THIS AFTERNOON AND EVENING. MODELS ARE FORECASTING A BREAK FOR A FEW HOURS TONIGHT...AND THE NEWER DATA IS CONSISTENT...WILL END UP ADJUSTING POP VALUES DOWNWARD FOR A FEW HOURS TONIGHT. MAIN VSBY RESTRICTIONS DURING THE DAY WILL BE IN SHRA/TSRA. OVERNIGHT...AS EASTERLY FLOW CONTINUES CIGS MAY BEGIN TO LOWER...ESPECIALLY EAST OF THE BLUE RIDGE. IN ADDITION...VSBYS WILL BE REDUCED IN SHRA/TSRA. WITH EASTERLY FLOW...MONDAY MORNING MAY BEGIN WITH A PERIOD OF IFR CIGS ESPECIALLY AT CHO/MRB/IAD PER SREFS/MAV/MET GUIDANCE. EXPECT SOME IMPROVEMENT DURING THE DAYTIME...HOWEVER TROPICAL MOISTURE WILL LEAD TO SHOWERS AND A FEW THUNDERSTORMS FOR THE REST OF MONDAY INTO TUESDAY. HEAVY DOWNPOURS AFFECTING THE TERMINALS DURING THIS TIME COULD PRODUCE BRIEF LIFR/IFR VSBYS. UNSETTLED WEATHER MAY CONTINUE INTO WEDNESDAY AS A FRONT/LOW PRESSURE MOVES THROUGH...THEN A REINFORCING FRONT ON THURSDAY SHOULD USHER IN A WIND SHIFT/DRIER WEATHER TO END THE WEEK. && .MARINE... A WEAK FRONTAL BOUNDARY WILL REMAIN STALLED ACROSS THE BAY THROUGH TONIGHT...AND THEN PUSH NORTHWARD DURING THE DAY ON MONDAY. PRECIPITATION WILL FOCUS ALONG THIS BOUNDARY...WITH SHRA/TSRA LIKELY. NO HEADLINES ANTICIPATED THROUGHT TONIGHT...BUT STRONGER THUNDERSTORMS MAY NECESSITATE SPECIAL MARINE WARNINGS. REMNANTS OF ISAAC WILL BRING UNSETTLED CONDITIONS THROUGH WEDNESDAY. EAST/SOUTHEAST WINDS MONDAY MAY FLIRT WITH SCA CRITERIA ON THE LOWER BAY/TIDAL POTOMAC LATE MONDAY/MONDAY NIGHT...BUT SCA APPEARS MORE LIKELY WITH WINDS SHIFTING THE SOUTH TUESDAY AFTERNOON/EVENING. && .TIDES/COASTAL FLOODING... TIDES THIS MORNING ARE AT NORMAL VALUES...BUT WITH AN EAST/SOUTHEAST FLOW DEVELOPING THROUGH MONDAY...EXPECT ANOMALIES TO BE ON THE INCREASE. WATER LEVELS SHOULD BE FINE THROUGH TONIGHT...BUT SENSITIVE LOCATIONS SUCH AS ANNAPOLIS AND ALEXANDRIA MAY START TO GET CLOSE TO MINOR TIDAL FLOODING THRESHOLDS STARTING WITH HIGH TIDE ON MONDAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && UPDATE...LISTEMAA
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 508 AM EDT SUN SEP 2 2012 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 031000- CHESAPEAKE BAY NORTH OF POOLES ISLAND MD- CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT MD- CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH MD- CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT MD- CHESAPEAKE BAY FROM DRUM POINT MD TO SMITH POINT VA- TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD MD- TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND MD- TIDAL POTOMAC FROM COBB ISLAND MD TO SMITH POINT VA- PATAPSCO RIVER INCLUDING BALTIMORE HARBOR- CHESTER RIVER TO QUEENSTOWN MD-EASTERN BAY- CHOPTANK RIVER TO CAMBRIDGE MD AND THE LITTLE CHOPTANK RIVER- PATUXENT RIVER TO BROOMES ISLAND MD- TANGIER SOUND AND THE INLAND WATERS SURROUNDING BLOODSWORTH ISLAND-DISTRICT OF COLUMBIA-NORTHERN BALTIMORE-HARFORD- SOUTHERN BALTIMORE-PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS- CALVERT-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX- ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA- KING GEORGE- 508 AM EDT SUN SEP 2 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MARYLAND PORTION OF THE CHESAPEAKE BAY...TIDAL POTOMAC RIVER...AND ADJACENT COUNTIES IN CENTRAL MARYLAND AND NORTHERN VIRGINIA AS WELL AS THE DISTRICT OF COLUMBIA. .DAY ONE...TODAY AND TONIGHT THERE IS THE POTENTIAL FOR LOCALLY HEAVY RAINFALL AND LOCALIZED FLASH FLOODING THIS AFTERNOON AND EVENING. ISOLATED THUNDERSTORMS COULD ALSO PRODUCE LOCALLY DAMAGING WIND GUSTS THIS AFTERNOON. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY MODERATE TO HEAVY RAINFALL COULD LEAD TO LOCALIZED FLASH FLOODING MONDAY THROUGH TUESDAY. A SMALL CRAFT ADVISORY MAY BE NEEDED OVER PORTIONS OF THE WATERS TUESDAY. MINOR COASTAL FLOODING ALONG THE WESTERN SHORE OF THE CHESAPEAKE BAY AND THE TIDAL POTOMAC RIVER IS POSSIBLE MONDAY INTO THE MIDDLE PART OF NEXT WEEK...PARTICULARLY FOR SENSITIVE LOCATIONS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY. MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504- WVZ050>053-055-501>506-031000- WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD- EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-AUGUSTA- ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-NELSON- ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-LOUDOUN-ORANGE-CULPEPER- NORTHERN FAUQUIER-SOUTHERN FAUQUIER-WESTERN HIGHLAND- EASTERN HIGHLAND-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-HARDY- WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL- WESTERN PENDLETON-EASTERN PENDLETON- 508 AM EDT SUN SEP 2 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN WEST VIRGINIA... NORTHERN AND CENTRAL VIRGINIA...AND CENTRAL AND WESTERN MARYLAND WITH THE EXCEPTION OF GARRETT COUNTY. .DAY ONE...TODAY AND TONIGHT THERE IS THE POTENTIAL FOR LOCALLY HEAVY RAINFALL AND LOCALIZED FLASH FLOODING THIS AFTERNOON AND EVENING. ISOLATED THUNDERSTORMS COULD ALSO PRODUCE LOCALLY DAMAGING WIND GUSTS THIS AFTERNOON. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY MODERATE TO HEAVY RAINFALL COULD LEAD TO LOCALIZED FLASH FLOODING MONDAY THROUGH TUESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
907 AM EDT SUN SEP 02 2012
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0434 PM TSTM WND DMG SMITH CROSSROADS 39.57N 78.23W
09/01/2012 MORGAN WV 911 CALL CENTER
TREE DOWN ON AUTUMN ACRES RD NEAR WINCHESTER GRADE RD.
&&
EVENT NUMBER LWX1201146
JACKSONPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
934 AM EDT SUN SEP 02 2012
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0451 PM TSTM WND DMG 1 WSW BERKELEY SPGS 39.62N 78.25W
09/01/2012 MORGAN WV 911 CALL CENTER
TREE DOWN ON QUAINT ACRES LN NEAR CACAPON RD.
&&
EVENT NUMBER LWX1201147
JACKSONSPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
233 PM EDT SUN SEP 2 2012
MDZ017-018-021915-
ST. MARYS MD-CALVERT MD-
233 PM EDT SUN SEP 2 2012
...STRONG THUNDERSTORM TO AFFECT ST. MARYS AND CALVERT COUNTIES...
AT 231 PM EDT...A STRONG THUNDERSTORM WAS LOCATED IN CENTRAL SAINT
MARYS COUNTY...ABOUT 2 MILES NORTH OF GREAT MILLS...DRIFTING SLOWLY
EAST.
LOCATIONS IMPACTED INCLUDE LEXINGTON PARK...PATUXENT RIVER NAS AND
SAINT MARYS CITY.
THIS STORM IS PRODUCING FREQUENT CLOUD TO GROUND LIGHTNING. MOVE
INDOORS IMMEDIATELY FOR YOUR SAFETY. IF YOU CAN HEAR THUNDER...YOU
ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING.
HEAVY RAIN...UPWARDS OF ONE AND ONE HALF INCH TOTAL...WITH THIS
STORM WILL REDUCE VISIBILITIES TO BELOW ONE MILE AND MAY CAUSE
PONDING OF WATER ON ROADWAYS AND LOW LYING AREAS. AVOID DRIVING
THROUGH FLOODED ROADWAYS.
A FEW WIND GUSTS OF 25 TO 35 MPH CAN BE EXPECTED WITH THIS STORM.
&&
LAT...LON 3812 7635 3824 7658 3835 7653 3834 7640
3832 7641 3832 7639 3830 7636 3828 7638
3824 7638 3817 7634
TIME...MOT...LOC 1831Z 287DEG 4KT 3826 7649
SMZThe Dover AFB radar (KDOX), 108 km away, was scanning. The volume nearest the first event began at 18:37 UTC.
1 flash flood. Local standard time, as filed.
Great Mills Road was closed due to high water in Lexington Park.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2012Every state in 2012This day in weather historyWarnings in Maryland, September 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: 413670.