A upper level trough moved over the region. An area of low pressure and southerly flow helped develop isolated showers and thunderstorms with strong winds and heavy rain.
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 upper level trough moved over the region. An area of low pressure and southerly flow helped develop isolated showers and thunderstorms with strong winds and heavy rain.
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 Aug 22, 2:00 AM EST, 3 hours 45 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 300 AM EDT WED AUG 22 2012 .SYNOPSIS... A LOW PRESSURE TROUGH WILL REMAIN OVER THE REGION THROUGH FRIDAY. HIGH PRESSURE WILL BUILD ACROSS THE MID ATLANTIC THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... DISCRETE VORT MAX...EVIDENT ON WV LOOP ACRS OH/WV/PA...AHEAD OF BROAD ULVL TROF IS INDUCING ENUF LIFT FOR ROGUE CLUSTER OF SHWRS/TSTMS TO MOVE WWD ACRS PORTIONS OF CWA. THIS ACTIVITY CONTS TO BE PROGGED TO DISSIPATE...BUT AS OF 7Z...HAS CROSSED BLUE RIDGE AND IS IMPACTING LOUDOUN COUNTY AND EXTREME WRN DC SUBURBS. ADDITIONAL ISOLATED SHWRS ARE NEAR SWRN CWA BORDER AND ACRS DELMARVA. STILL EXPECT PCPN TO WANE EARLY THIS MRNG...WITH DRY CONDS FCST THRU WED MRNG. CLOUD COVER IN ASSOCIATION WITH CNVCTN HAS LIMITED FOG DEVELOPMENT SOMEWHAT...BUT PATCHY FOG STILL ANTICIPATED ACRS WRN 2/3RD OF CWA AS NEARLY SATURATED BOUNDARY LYR RADIATIONALLY COOLS. SEASONABLY WARM TEMPS ERY THIS MRNG WILL CONT TDA AND TNGT...WITH MINIMA AND MAXIMA A FEW DEGS BELOW NRML FOR LATE AUG. WEAK SFC HIPRES WILL RESIDE IN THE VICINITY...BUT H5 TROF AXIS WILL REST W OF CWA TDA. WITH DIURNAL HEATING...ISOLATED/SCATTERED SHWRS AND SOME TSTMS SHUD DVLP BY AFTN...ESPECIALLY WRN ZONES. THIS ACTIVITY SHUD DIMINISH AFTN SUNSET TNGT...WITH POTENTIAL FOR PATCHY FOG AGAIN THU MRNG. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... 500MB TROUGH STILL OVERHEAD ON THURSDAY. AT THE SURFACE...A WEAK TROUGH IS SITUATED ALONG THE BLUE RIDGE MOUNTAINS. SLIGHT/LOW END CHANCE POPS ARE POSSIBLE ALONG AND WEST OF THE BLUE RIDGE MOUNTAINS...CLOSEST TO THE ENERGY FROM THE UPPER TROUGH. && .LONG TERM /FRIDAY THROUGH TUESDAY/... THE WEAK TROUGHING ALOFT REMAINS ACROSS THE CWFA THROUGH THE WEEKEND...BUT BEGINS TO BREAK DOWN BY EARLY NEXT WEEK. HOWEVER...ANOTHER 500MB TROUGH LOOKS TO COME THROUGH BY THE MIDDLE OF THE WEEK. AT THE SURFACE...HIGH PRESSURE REMAINS ACROSS THE MID ATLANTIC THROUGH THE MIDDLE OF NEXT WEEK. NO CHANGES MADE PAST DAY 4. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... TAFS GENERALLY PCPN-FREE...BUT AMENDMENT NECESSARY FOR KIAD...WHERE CLUSTER OF SHWRS WILL IMPACT BTWN 7-8Z. ADDITIONAL ISOLATED/SCT CNVCTN MAINLY W OF BALT AIRPORTS THIS ACTIVITY...BUT CONFIDENCE IN TIMING AND CVRG TOO LOW TO INTRODUCE IN TAFS ATTM. NO CIG RESTRICTIONS THRU TNGT...BUT OVNGT/ERY MRNG FOG IS OCCURRING AT KCHO AND MAY SPREAD TO MRB/IAD BEFORE SUNRISE. SIMILAR SCENARIO LIKELY TMW...WITH IFR CONDS MOSTLY LIKELY AT KIAD. WITH WEAK SFC HIPRES IN PLACE...WINDS WILL BE QUITE LIGHT INTO THU. PATCHY GROUND FOG IS POSSIBLE AT KCHO AND KIAD THROUGH THE END OF THE WEEK TOWARDS SUNRISE...BUT NO/CIG VSBY RESTRICTIONS ANTICIPATED DURING THE DAY. && .MARINE... LGT WINDS AND GENERALLY DRY CONDS INTO THU...WITH SFC HIPRES IN VICINITY. && .TIDES/COASTAL FLOODING... TIDAL ANOMALIES ARE AROUND 1/2 FOOT ABV NRML ERY THIS MRNG. EXPECTING LITTLE CHG IN THESE VALUES THRU TDA...WHICH WOULD PRECLUDE MINOR COASTAL FLOODING. STILL CANT RULE OUT INUNDATION WITH AFTN HIGH TIDE AT SENSITIVE LOCATIONS...BUT THREAT ATTM APPEARS MINIMAL. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && SYNOPSIS...NWL NEAR TERM...SBK SHORT TERM...NWL LONG TERM...NWL AVIATION...SBK/NWL MARINE...SBK/NWL TIDES/COASTAL FLOODING...SBK
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 501 AM EDT WED AUG 22 2012 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 231000- 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- 501 AM EDT WED AUG 22 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 NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504- WVZ050>053-055-501>506-231000- 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- 501 AM EDT WED AUG 22 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 NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
The Sterling radar (KLWX), 34 km away, was scanning. The volume nearest the first event began at 10:46 UTC.
1 flash flood. Local standard time, as filed.
Norbeck Road was under water near Avery Road and Rock Creek.
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, August 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: 409485.