A cold front crossed the Mid Atlantic from the west in the afternoon. An abundant amount of instability and wind shear led to the development of severe thunderstorms that produced damaging winds.
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 cold front crossed the Mid Atlantic from the west in the afternoon. An abundant amount of instability and wind shear led to the development of severe thunderstorms that produced damaging winds.
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 10, 2:12 PM EST, 58 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
312 PM EDT FRI AUG 10 2012
.SYNOPSIS...
A COLD FRONT WILL APPROACH THE MID ATLANTIC TODAY...THEN SLOWLY MOVE
EAST ACROSS THE REGION THROUGH SUNDAY MORNING. HIGH PRESSURE WILL
MOVE EAST ACROSS THE CENTRAL MID ATLANTIC SUNDAY THROUGH
MONDAY...BEFORE THE NEXT COLD FRONT CROSSES THE REGION ON TUESDAY.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
THE ATMOSPHERE HAS BEGUN TO DESTABILIZE AS A MID LEVEL DRY SLOT SEEN
ON WATER VAPOR CONTINUES TO PUNCH IN FROM THE WEST. THIS FEATURE
WILL HELP TO STEEPEN LAPSE RATES WHILE SKIES CONTINUE PARTLY CLOUDY
WITH RISING TEMPERATURES. ABUNDANT MOISTURE REMAINS IN PLACE WITH
PWATS RUNNING BETWEEN 1.5 AND 2 INCHES. SHEAR PROFILES ARE ALSO
ADEQUATE. WE EXPECT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS
TO DEVELOP AHEAD OF AN EASTWARD ADVANCING COLD FRONT THIS EVENING
AND TONIGHT. SOME OF THE STORMS WILL STILL BE CAPABLE OF PRODUCING
DAMAGING WIND GUSTS...SMALL HAIL AND HEAVY DOWNPOURS WHICH COULD
LEAD TO LOCALIZED FLASH FLOODING. A FEW LOCALES RECEIVED UPWARDS OF
5 TO 6 INCHES OF RAINFALL FROM LAST EVENINGS STORMS AND STILL
MANAGED TO ABSORB MUCH OF THAT RAINFALL. OPTED AGAINST A FLASH FLOOD
WATCH FOR THIS EVENT GIVEN THE ABNORMALLY DRY RECENT STRETCH.
SHOWER AND THUNDERSTORM CHANCES CONTINUE TONIGHT WITH COVERAGE
DECREASING AND SHIFTING EAST ON SATURDAY. HIGHEST POP CHANCES WILL
BE RELEGATED TO THE METRO AREAS AND EAST TO THE COASTAL WATERS.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
SATURDAY...COLD FRONT WILL BE STALLED OUT ROUGHLY ALONG THE I-95
CORRIDOR THROUGH MD/VA WITH ONGOING SHOWERS AND THUNDERSTORMS EAST
OF THERE. DEEP DRY SLOT AND PRESSURE RISES SHOULD KEEP AREAS WEST OF
THE CORRIDOR DRY. HOPEFULLY AREAS OF SRN MD EXPERIENCING DROUGHT
WILL ENJOY EXTENDED PRECIP ON SATURDAY. QPF ON THE ORDER OF A COUPLE
TENTHS. NAM12 TEMPS WERE BLENDED IN TO REDUCE MAX TEMPS FOR AREAS
EAST OF THE I-95 CORRIDOR WHERE DESPITE GUSTY SLY FLOW THE PRECIP
AND CLOUDS SHOULD LIMIT TEMPS. EXPECT MAX TEMPS LOW TO MID 80S
ACROSS THE AREA.
SATURDAY NIGHT...COLD FRONT BEGINS TO EASE EAST WITH WEST EDGE OF
PRECIP SLIDING TO THE EASTERN SHORE. MAYBE A FEW MORE HUNDREDTHS OF
RAINFALL FOR FAR SRN MD BEFORE TAPERING OFF AFTER MIDNIGHT. DRY
ELSEWHERE AS UPR TROUGH AXIS REACHES THE MID APPALACHIANS. MIN TEMPS
UPR 50S WEST OF THE BLUE RIDGE...LOW MID 60S EAST /AROUND 70F URBAN
AND NEAR SHORE/.
SFC HIGH PRESSURE SHIFTS EAST ACROSS THE CENTRAL MID ATLANTIC SUNDAY
INTO MONDAY...EXPECT DRY WEATHER WITH NEAR NORMAL MAX TEMPS OF MID
TO UPR 80S BOTH DAYS. AS THE HIGH PUSHES EAST MONDAY SOME SLY FLOW
UP THE CHESAPEAKE BAY /ALONG WITH BAY BREEZES/ MAY AID DEEP MOIST
CONVECTION...SO SLIGHT CHANCES FOR TSTMS WERE ADDED FOR SRN MD.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A SERIES OF SHORTWAVES LOOK TO CROSS THE MID ATLANTIC TUESDAY
THROUGH THE REST OF THE WORK WEEK. POSSIBLE SCATTERED THUNDERSTORMS
WITH EACH DISTURBANCE...TUESDAY AND FRIDAY HIGHLIGHTED AS OF THIS
TIME. SLY FLOW AHEAD OF THIS WAVE WILL BRING TEMPS BACK ABOVE
NORMAL...MAX TEMPS AROUND 90F TUESDAY...WITH CLOUDS AND PRECIP
LIMITING TEMPS TO AROUND NEAR NORMAL WEDNESDAY TO FRIDAY.
&&
.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
VFR TO MVFR CONDITIONS EXPECTED INTO THE LATE AFTERNOON OR EARLY
EVENING. SHOWERS AND THUNDERSTORMS WILL DEVELOP AND SPREAD ACROSS
THE REGION. EACH TERMINAL WILL HAVE A MEDIUM CONFIDENCE OF RECEIVING
DIRECT IMPACT FROM THUNDERSTORMS. STRONG GUSTY WINDS AND HEAVY
DOWNPOURS WILL BE THE MAIN THREATS WITH PEAK IMPACT TIMES BETWEEN
22-03Z. FOG AND LOW CLOUDS WILL BECOME A CONCERN AFTER MIDNIGHT WITH
REDUCED VSBYS. SHOWER AND STORM CHANCES SHIFT TO THE EASTERN
SECTIONS SATURDAY AFTERNOON AND EVENING.
STALLED FRONT ALONG BALT-WASH CORRIDOR SATURDAY WITH MVFR CIGS/VSBYS
POSSIBLE IN SHOWERS AND THUNDERSTORMS ALONG AND EAST OF THERE...VFR
WEST. HIGH PRESSURE/VFR OUTSIDE OF ANY MORNING FOG SUNDAY AND MONDAY
WITH AN ACTIVE WEATHER PERIOD STARTING AGAIN ON TUESDAY.
&&
.MARINE...
SMALL CRAFT CONDITIONS STARTING TO TAKE SHAPE OVER PORTIONS OF THE
WATERS AND THIS TREND WILL CONTINUE OVERNIGHT. ADDITIONAL GUSTY
SOUTHERLY FLOW AND CHANNELING WILL TAKE SHAPE SATURDAY INTO SUNDAY.
SMALL CRAFT ADVISORY HAS BEEN POSTED.
STALLED COLD FRONT JUST EAST OF THE CHESAPEAKE BAY SATURDAY BRINGING
SLY FLOW. STARTED A NEW SMALL CRAFT ADVISORY NOON SATURDAY FOR SLY
CHANNELING THAT WILL CONTINUE INTO LATE SATURDAY NIGHT BEFORE THE
FRONT PUSHES THROUGH. HIGH PRESSURE/LIGHT FLOW EXPECTED SUNDAY INTO
MONDAY. SLY FLOW LATER MONDAY THROUGH MIDWEEK. WILL HAVE TO WATCH
FOR EVENING CHANNELING FOR POTENTIAL SCAS.
&&
.TIDES/COASTAL FLOODING...
SOUTHERLY FLOW 15-20KT BROUGHT POSITIVE ANOMALIES BETWEEN 0.7-1
FT ACROSS THE WATERS. HOWEVER...NEAP TIDES AT HALF MOON WILL KEEP
THE COASTAL FLOODING RISK LOW. SLY FLOW WILL REMAIN HIGH THROUGH
TONIGHT... SO MINOR FLOODING MAY BE POSSIBLE STARTING ON SATURDAY.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR
ANZ530>533-535>542.
SMALL CRAFT ADVISORY FROM 6 PM SATURDAY TO 6 AM EDT SUNDAY FOR
ANZ531-539.
SMALL CRAFT ADVISORY UNTIL 8 AM EDT SATURDAY FOR ANZ534-543.
SMALL CRAFT ADVISORY FROM NOON SATURDAY TO 6 AM EDT SUNDAY FOR
ANZ532>534-537-540-541-543.
&&
SYNOPSIS...BAJ/KRW
NEAR TERM...KRW
SHORT TERM...BAJ
LONG TERM...BAJ
AVIATION...BAJ/KRW
MARINE...BAJ/KRW
TIDES/COASTAL FLOODING...BAJHAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 328 PM EDT FRI AUG 10 2012 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 111145- 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- 328 PM EDT FRI AUG 10 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...THIS AFTERNOON AND TONIGHT A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL THE WATERS...THEN ONLY THE LOWEST MARYLAND CHESAPEAKE BAY OVERNIGHT. SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS EVENING INTO THE OVERNIGHT. SOME OF THE STORMS COULD BE SEVERE AND CAPABLE OF PRODUCING DAMAGING WIND GUSTS...HAIL AND LOCALIZED FLASH FLOODING. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY A SMALL CRAFT ADVISORY IS IN EFFECT FOR PORTIONS OF THE WATERS SATURDAY AFTERNOON THROUGH SATURDAY NIGHT. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING. MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504- WVZ050>053-055-501>506-111145- 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- 328 PM EDT FRI AUG 10 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...THIS AFTERNOON AND TONIGHT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CONTINUE WEST OF THE BLUE RIDGE LATE THIS AFTERNOON AND SPREAD EAST THIS EVENING INTO THE OVERNIGHT. SOME OF THE STORMS COULD BE SEVERE AND CAPABLE OF PRODUCING DAMAGING WIND GUSTS...HAIL AND LOCALIZED FLASH FLOODING. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED LATER THIS AFTERNOON AND EVENING. JACKSON
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
152 PM EDT FRI AUG 10 2012
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0655 PM TSTM WND DMG 1 WNW CLEAR BROOK 39.26N 78.12W
08/09/2012 FREDERICK VA PUBLIC
TREES DOWN ALONG PUNKIN RIDGE RD
&&
EVENT NUMBER LWX1201066
JACKSONThe Sterling radar (KLWX), 82 km away, was scanning. The volume nearest the first event began at 20:09 UTC.
2 thunderstorm wind. Local standard time, as filed.
Large trees knocked down wires.
Multiple trees down in Hagerstown and large trees down on East North Avereport.
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: 407876, 407877.