A backdoor cold front stalled out over the region on the 12th while and upper-level disturbance passed through the area. A hot and humid air mass ahead of the cold front produced moderate amounts of instability.
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 backdoor cold front stalled out over the region on the 12th while and upper-level disturbance passed through the area. A hot and humid air mass ahead of the cold front produced moderate amounts of instability. Some thunderstorms that developed were able to produce damaging wind and large hail.
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 12, 10:28 AM EST, 3 hours 2 minutes earlier.
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1128 AM EDT THU AUG 12 2010
.SYNOPSIS...
A BACKDOOR COLD FRONT WILL CROSS THE REGION THROUGH TONIGHT...
BRINGING SHOWERS AND THUNDERSTORMS. ONSHORE FLOW WILL PERSIST
BEHIND THE BOUNDARY FRIDAY THROUGH THE WEEKEND. ANOTHER COLD
FRONT WILL APPROACH FROM THE WEST EARLY NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
ONGOING LULL AFTER EVENTFUL MRNG WX WILL PERSIST FOR A COUPLE OF
HOURS AS ATMOSPHERE RECOVERS AMID AMPLE HEATING THRU MUCH OF SRN
AND CNTRL PORTIONS OF FCST AREA. SHRTWV TROF OVER S-CNTRL PA WILL
CONT ITS SEWD MVMT AND WILL DRAW DRY AIR IN ALOFT. AT THE SAME
TIME...HOWEVER...WARM AIR ADVCTN WILL OCCUR ALOFT...SERVING TO
WEAKEN LAPSE RATES SOMEWHAT.
SPCLY SWRN SECTIONS...WHERE NO TSTMS HAVE YET OCCURRED...88F/70F
WILL YIELD MDT INSTBY. CU FIELD ALREADY BEING INVIGORATED...BUT
THESE ARE FLAT ATTM. WITH APRCH OF WAVE AND CONTD HEATING...XPC
TSTMS TO DVLP EARLY THIS AFTN. DRY AIR ALOFT WILL ENHANCE WIND
POTENTIAL AMID AMPLE SHEAR FOR UPDRAFT ORGANIZATION. CHGS TO FCST
WERE MINIMAL...PRIMARILY TO REFLECT SHORT TERM TRENDS IN PCPN.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
BNDRY WL RMN OVR THE AREA TNGT. M CLDY SKIES. CHCS OF EVE CNVCTN
SHOULD GIVE WAY TO A STABILIZATION AFTR MDNGT...LOSING CHC OF T. E
OF THE MTNS LO LVL ERLY FLOW WL PERSIST PROVIDING THAT STABILIZING
EFFECT. LOW TEMPS IN LM70S IN CITIES/ALONG BAY TO M60S IN THE
HIGHLANDS.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
A BACKDOOR COLD FRONT WILL STALL OUT TO OUR SOUTH AND WEST ON FRIDAY
WHILE SURFACE HIGH BUILDS OVER NEW ENGLAND. AN ONSHORE FLOW WILL
PUMP IN MOISTURE FROM THE ATLANTIC...RESULTING IN MORE CLOUDS ALONG
WITH COOLER CONDITIONS. HOWEVER...IT WILL REMAIN HUMID WITH MOISTURE
MOVING IN OFF THE OCEAN. SCATTERED SHOWERS ARE POSSIBLE DUE TO THE
ONSHORE FLOW. SCATTERED T-STORMS ARE ALSO POSSIBLE ACROSS CENTRAL
VIRGINIA AS WELL AS LOCATIONS WEST OF THE BLUE RIDGE MOUNTAINS WHERE
THERE WILL BE MORE INSTABILITY FURTHER AWAY FROM THE SURFACE HIGH.
HIGH PRESSURE OFF THE NEW ENGLAND COAST WILL CONTINUE TO PROVIDE AN
ONSHORE FLOW THROUGH THE WEEKEND. SCATTERED SHOWERS/T-STORMS ARE
POSSIBLE DURING THIS TIME...ESPECIALLY ACROSS CENTRAL VIRGINIA INTO
THE POTOMAC HIGHLANDS FURTHER AWAY FROM THE SURFACE HIGH.
THE SURFACE HIGH WILL SHIFT EAST EARLY NEXT WEEK AS A TROUGH OF LOW
PRESSURE OVER THE GREAT LAKES SHIFTS TOWARD NEW ENGLAND. THE COLD
FRONT ASSOCIATED WITH THE TROUGH WILL APPROACH THE REGION FROM THE
WEST...BUT IT WILL LIKELY STALL OUT OVER THE MID-ATLANTIC THROUGH
THE MIDDLE PORTION OF THE WEEK...BRINGING UNSETTLED CONDITIONS.
&&
.AVIATION /15Z THURSDAY THROUGH MONDAY/...
BRIEF IFR CIGS NEAR KBWI XPCD IN WAKE OF CNVCTN THIS MRNG.
OTHERWISE...VFR CONDS XPCD THRU THIS AFTN AND EVE. MVFR-IFR CONDS
ARE LKLY IN ANY TSTMS THAT DVLP THIS AFTN AND EVE ALONG SFC BNDRY
AND ON HIGHER TERRAIN. TSTMS WILL MOVE S OR SE.
A BACKDOOR BOUNDARY WILL STALL OUT TO OUR SOUTH AND WEST FRIDAY. AN
ONSHORE FLOW WILL BRING SUBVFR CIGS ALONG WITH THE CHANCE FOR
SHOWERS AND THUNDERSTORMS.
AN ONSHORE FLOW WILL PERSIST THROUGH THE WEEKEND. THE BEST CHANCE
FOR CONVECTION WILL BE ACROSS THE WESTERN TERMINALS. A COLD FRONT
WILL APPROACH THE TERMINALS EARLY NEXT WEEK...BRINGING A BETTER
CHANCE FOR CONVECTION.
&&
.MARINE...
ELY WINDS WILL CONT ACRS WATERS TDA TO E OF SFC BNDRY. TSTMS MAY
DVLP AGAIN THIS AFTN AND EVE AND LKLY WILL IMPACT THE WATERS.
SPECIAL MARINE WRNGS LKLY WILL BE NEEDED.
SMALL CRAFT ADZY WAS RETAINED FRI AFTN AND EVE AS INHERITED. INCRG
GUSTS PSBL AS SFC BNDRY MOVES SWWD AND HIPRES BUILDS FROM THE NE.
SCATTERED SHOWERS ARE POSSIBLE FRIDAY WITH PLENTY OF MOISTURE
MOVING IN FROM THE ATLANTIC.
A COLD FRONT WILL APPROACH THE WATERS EARLY NEXT WEEK...BRINGING A
BETTER CHANCE FOR SHOWERS AND T-STORMS.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 2 PM FRIDAY TO MIDNIGHT EDT FRIDAY
NIGHT FOR ANZ530>534-537>543.
&&
UPDATE...KRAMAR
PREV DISCUSSION...WOODY!/LASORSAHAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 113 PM EDT THU AUG 12 2010 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 131315- 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- 113 PM EDT THU AUG 12 2010 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 THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR THE WESTERN AND SOUTHERN SUBURBS OF WASHINGTON DC AND THE NORTHERN PIEDMONT REGION. THE COMBINATION OF INCREASING LOW- LEVEL MOISTURE...MODERATE INSTABILITY AND AN APPROACHING UPPER-LEVEL DISTURBANCE WILL RESULT IN THE REDEVELOPMENT OF THUNDERSTORMS THIS AFTERNOON. SOME OF THE STORMS COULD BECOME SEVERE AND WILL BE CAPABLE OF PRODUCING DAMAGING WIND GUSTS...LARGE HAIL AND TORRENTIAL RAIN. SPECIAL MARINE WARNINGS MAY BE NEEDED. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MARYLAND PORTION OF THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER FRIDAY AND FRIDAY EVENING. PERSISTENT ONSHORE FLOW IS EXPECTED BEHIND A BACKDOOR COLD FRONT FRIDAY THROUGH THE WEEKEND. THE ONSHORE FLOW WILL LEAD TO INCREASED TIDAL ANOMALIES WHICH MAY CAUSE MINOR COASTAL FLOODING NEAR TIMES OF HIGH TIDE ACROSS THE TIDAL POTOMAC RIVER AND THE WESTERN SHORE OF THE CHESAPEAKE BAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION LIKELY WILL BE NEEDED THIS AFTERNOON. MDZ003>005-009-010-501-502-VAZ021-025>031-036>040-042-050-051-501- 502-WVZ050>055-501>504-131315- WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD- EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-HIGHLAND- AUGUSTA-ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE- NELSON-ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-LOUDOUN-ORANGE- CULPEPER-NORTHERN FAUQUIER-SOUTHERN FAUQUIER-HAMPSHIRE-MORGAN- BERKELEY-JEFFERSON-PENDLETON-HARDY-WESTERN GRANT-EASTERN GRANT- WESTERN MINERAL-EASTERN MINERAL- 113 PM EDT THU AUG 12 2010 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 THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR THE NORTHERN PIEDMONT...THE CENTRAL FOOTHILLS...THE CENTRAL AND NORTHERN SHENANDOAH VALLEY...NORTHERN VIRGINIA AND PORTIONS OF THE EASTERN WEST VIRGINIA PANHANDLE. THE COMBINATION OF INCREASING LOW-LEVEL MOISTURE...MODERATE INSTABILITY AND AN APPROACHING UPPER-LEVEL DISTURBANCE WILL RESULT IN THUNDERSTORMS THIS AFTERNOON AND EVENING. SOME OF THE STORMS COULD BECOME SEVERE AND WILL BE CAPABLE OF PRODUCING DAMAGING WIND GUSTS...LARGE HAIL AND TORRENTIAL RAIN. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION LIKELY WILL BE NEEDED THIS AFTERNOON. KRAMAR
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1121 AM EDT THU AUG 12 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0655 AM TSTM WND DMG GAITHERSBURG 39.14N 77.22W
08/12/2010 MONTGOMERY MD BROADCAST MEDIA
*** 14 INJ *** TREE INTO GARDEN APTS
&&
EVENT NUMBER LWX1000853
STRONGPRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1131 AM EDT THU AUG 12 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0604 AM TSTM WND DMG 3 WNW IJAMSVILLE 39.38N 77.36W
08/12/2010 FREDERICK MD 911 CENTER
TREE DOWN REICHS FORD RD
&&
CORRECTED EVENT TIME
EVENT NUMBER LWX1000829
KRAMARPRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1135 AM EDT THU AUG 12 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0624 AM TSTM WND DMG 4 NNW CLARKSBURG 39.29N 77.31W
08/12/2010 FREDERICK MD 911 CENTER
TREES DOWN ON ROUTE 75 NEAR URBANA
&&
CORRECTED EVENT TIME...LOCATION...REMARKS
EVENT NUMBER LWX1000830
KRAMARPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1243 PM EDT THU AUG 12 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0915 AM WATER SPOUT 14 ESE COVE POINT 38.28N 76.16W
08/12/2010 ANZ543 MD PUBLIC
WATERSPOUTS IN THE HONGA RIVER NEAR BENTLEY POINT
DAMAGED SOME BOAT CANOPIES. RELAYED BY WFO AKQ. TIME
ESTIMATED FROM TDWR
&&
EVENT NUMBER LWX1000854
KRAMARPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
153 PM EDT THU AUG 12 2010
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0655 AM TSTM WND DMG GAITHERSBURG 39.14N 77.22W
08/12/2010 MONTGOMERY MD BROADCAST MEDIA
LARGE TREE ON HOUSE.
&&
EVENT NUMBER LWX1000855
STRONGSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 212 PM EDT THU AUG 12 2010 VAZ031-042-WVZ053-121845- CLARKE VA-LOUDOUN VA-JEFFERSON WV- 212 PM EDT THU AUG 12 2010 ...STRONG THUNDERSTORMS TO AFFECT CLARKE...LOUDOUN AND JEFFERSON COUNTIES... AT 211 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER SUMMIT POINT...MOVING SOUTHEAST AT 25 MPH. HEAVY RAIN WITH THIS STORM MAY REDUCE VISIBILITIES TO BELOW ONE MILE AND MAY CAUSE PONDING OF WATER ON ROADWAYS. WIND GUSTS OF 40 TO 50 MPH CAN BE EXPECTED WITH THIS STORM. && LAT...LON 3916 7756 3898 7775 3921 7805 3933 7794 TIME...MOT...LOC 1811Z 306DEG 20KT 3922 7791 PELOQUIN
The Sterling radar (KLWX), 37 km away, was scanning. The volume nearest the first event began at 18:28 UTC.
20 thunderstorm wind, 4 hail. Local standard time, as filed.
A large tree was down along Route 7 near Mountain Ridge Lane.
A large tree was down along Route 7 between Williams Gap Road and Snickersville Turnpike.
Large branches and power lines were down on US 50 west of Middleburg.
Tree limbs were down near Middleburg.
Trees and wires were down about two miles northwest of Halfway.
Several trees and wires were blown down near Halfway.
Several trees were down along highway 50 between Middleburg and Aldie.
Several trees were down near The Plains.
Several trees were blown near Turnbull.
A tree fell down onto a fence. the tree was twelve inches diameter.
A large tree was down in the Haymarket area.
A tree fell into a home at Remington.
A few branches of two inches in diameter were down near Elkwood.
Tree limbs about four inches in diameter were blown down near Sumerduck.
Ping pong ball sized hail was reported near Sumerduck.
Trees were down on Rexburg Court near Rhode Island Drive.
Hail up to quarters in size was reported along Dishpan Lane near Brooke.
Hail two inches in diameter was reported on Halls Road near Richardsville.
Numerous large limbs were blown off in very strong winds along Halls Road.
A large tree was down near the intersection of Brock Road and Orange Plank Road.
A track of patchy damage was noted from near the Stafford County Landfill to Deshazo Lane. Trees were snapped and a cluster of shingles was removed from the roof of a house.
Numerous trees were down near the intersection of Robert E Lee Drive and Gibson Lane.
Quarter sized hail was reported on Millwood Lane near Alsop.
Trees were blocking the roadway along Courthouse Road.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Virginia in 2010Every state in 2010This day in weather historyWarnings in Virginia, August 2010
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: 257034, 257033, 255399, 255413, 255405, 255402, 255407, 255410, 255415, 255412, 255414, 255416, 255417, 255418, 255426, 255422, 255430, 255428, 257001, 257002, 257005, 257003, 255429, 257006.