Deep layer easterly flow allowed a surge of Atlantic moisture to spread westward across the Chesapeake Bay. Scattered slowly moving showers developed as this area of enhanced moisture moved over lower southern Maryland, creating an isolated flash flood event in Anne Arundel County.
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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.
Deep layer easterly flow allowed a surge of Atlantic moisture to spread westward across the Chesapeake Bay. Scattered slowly moving showers developed as this area of enhanced moisture moved over lower southern Maryland, creating an isolated flash flood event in Anne Arundel County.
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 6, 4:40 PM EST, 41 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
540 PM EDT SUN SEP 6 2009
.SYNOPSIS...
HIGH PRESSURE OVER NEW ENGLAND WILL MOVE OFF THE COAST OF MAINE
EARLY IN THE WEEK. LOW PRESSURE OFF THE GEORGIA COAST WILL SLOWLY
MOVE OFF THE VIRGINIA COAST BY MIDWEEK.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
LINE OF SHOWERS MOVING ONSHORE THE WESTERN SHORE OF THE CHESAPEAKE
CONTINUES TO MAKE PROGRESS INLAND AND HOLD TOGETHER. NO LIGHTNING
WITH THIS ACTIVITY. THIS FEATURE WAS NOT WELL ANALYZED BY THE
LATEST RUN OF THE LOCAL WRF. HAVE GONE AHEAD AND SPREAD CHANCE POPS
TO THE BLUE RIDGE. DEWPOPINTS ARE SOMEWHAT LOWER WEST OF THE BLUE
RIDGE...SO NOT EXPECTING MUCH OF THIS ACTIVITY TO SURVIVE INTO TE
SHENANDOAH VALLEY. OTHERWISE...NO OTHER CHANGES AT THIS TIME.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
LOW ALONG COASTAL CAROLINA ORGANIZES A BIT AND DRIFTS NORTHWARD
TOMORROW. INCREASED ONSHORE FLOW WITH LOW TO THE SOUTH/HIGH TO THE
NORTH DRAPES THE CWA WITH CLOUDS...GENERALLY INCREASING RAIN CHANCES
/ESPECIALLY EAST AND SOUTH/ THROUGH THE DAY MONDAY. TROUGH TO THE
WEST ONLY DRIFTS EAST. CHANCE OF SHOWERS CONTINUES FOR WESTERN
RIDGES. LITTLE IF ANY SUN LEADS TO COOLER CONDITIONS...MID TO
UPPER 70S.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
DECENT AGREEMENT AMONG GFS ENSEMBLE MEMBERS IN UPR AIR PATTERN
THRU MEDIUM RNG. CUTOFF UPR LOW CURRENTLY TO SW WILL RMN IN FCST AS
UPR RDG MOVES ACRS N-CNTRL CANADA. CUTOFF LOW XPCD TO MAKE SLOW
EWD PROGRESS.
SFC LOPRES DVLPS ALONG CAROLINA COAST AS SHRTWV TROFS MOVE AROUND
SRN PERIPHERY OF CUTOFF LOW. PRESSURE GRADIENT WILL TIGHTEN IN
RESPONSE...WITH INCRD ELY-NNELY FLOW AS LOW BUILDS NEWD. SYNOPTIC
EVOLUTION WILL RESEMBLE A COLD AIR DAMMING PATTERN...WITH SVRL
DAYS OF BKN-OVC SKIES AND PSBLTY OF LGT PCPN MOST AREAS. ATTM...
PCPN SEEMS MOST LKLY IN SERN ZONES...CLOSEST TO XPCD PATH OF SFC
LOPRES.
HAVE CONTD SLGT CHC-CHC POPS THRU MUCH OF THIS WEEK. LARGE ENSEMBLE
SPREAD IN EXTENDED PDS GIVES LITTLE CONFIDENCE TO FCST FOR LATE IN
THE WEEK.
AS WITH PREV GRIDS...HAVE CONTD TREND OF LWR MAXIMA AND INCRD CLD
CVR THRU MUCH OF THIS WEEK.
&&
.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
VFR CONDITIONS DEGRADE TO MVFR CIGS/VSBYS /SOME ISO IFR POSSIBLE/ BY
THIS EVENING THEN THROUGH TONIGHT AS EASTERLY FLOW INCREASES LOW
LEVEL MOISTURE ACROSS THE MID ATLANTIC. MVFR CIGS TOMORROW WITH RAIN
CHANCES INCREASING FROM THE SOUTH AND EAST THROUGH THE DAY AS LOW
PRESSURE ALONG THE CAROLINA COAST MOVES NORTH.
SUB-VFR CIGS AND REDUCED VSBYS IN LGT RAIN ARE PSBL BGNG MON NGT
AND CONTG ON AND OFF FOR SVRL DAYS AS ELY FETCH REINFORCES MSTR
ATOP A SFC RDG AXIS.
&&
.MARINE...
ELY FLOW INCREASES THROUGH THE REST OF THE AFTERNOON AND
EVENING...ISOLATED SHOWERS THROUGH THE EVENING HOURS. SMALL CRAFT
NOW VALID FOR CHESAPEAKE BAY AND TIDAL POTOMAC BELOW COBB ISLAND.
EASTERLY FLOW CONTINUES TOMORROW WITH A COASTAL LOW CURRENTLY
ALONG THE CAROLINAS DRIFTING NORTH. SCA CURRENTLY FOR BAY SOUTH OF
DRUM POINT...MAY NEED TO BE EXPANDED.
DVLPG COASTAL SFC LOPRES WILL INCR PRESSURE GRADIENT ACRS LWR
MARINE ZONES CONTG THRU MON EVE. SMALL CRAFT ADZY IN EFFECT THRU
MON EVE. SMALL CRAFT ADZY CONDITIONS PSBL WED AFTN AND EVE AS SFC
LOPRES PASSES TO E OF RGN.
&&
.TIDES/COASTAL FLOODING...
DVLPG COASTAL SFC LOPRES WILL INCR ELY FLOW ACRS CHSPK BAY...AND
MAY YIELD POSITIVE TIDAL ANOMALIES. TEMPORAL DURATION OF ELY FLOW
UNCERTAIN...BUT IT COULD BE SUFFICIENT FOR MINOR COASTAL FLOODING
DURG MIDDLE PORTION OF THIS WEEK.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 AM EDT MONDAY FOR ANZ530>534-
537>543.
SMALL CRAFT ADVISORY FROM NOON TO 10 PM EDT MONDAY FOR ANZ534-
537-543.
&&
LISTEMAAHAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 341 PM EDT SUN SEP 6 2009 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 071000- 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- 341 PM EDT SUN SEP 6 2009 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 THROUGH 2 AM FOR THE MARYLAND CHESAPEAKE BAY AND THE LOWER TIDAL POTOMAC RIVER. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY A SMALL CRAFT ADVISORY IS IN EFFECT FROM NOON TO 10 PM MONDAY FOR THE MARYLAND CHESAPEAKE BAY FROM DRUM POINT TO SMITH POINT INCLUDING TANGIER SOUND...AND THE TIDAL POTOMAC FROM COBB ISLAND TO SMITH POINT. SMALL CRAFT ADVISORY THRESHOLD CONDITIONS WILL BE POSSIBLE WEDNESDAY AFTERNOON AND EVENING FOR PORTIONS OF THE CHESAPEAKE BAY AND TIDAL POTOMAC RIVER. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED THROUGH TONIGHT. MDZ003>005-009-010-501-502-VAZ021-025>031-036>042-050-051- WVZ050>055-501>504-071000- 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-FAUQUIER-LOUDOUN- ORANGE-CULPEPER-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-PENDLETON- HARDY-WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL- 341 PM EDT SUN SEP 6 2009 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 NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED THROUGH TONIGHT.
The Sterling radar (KLWX), 75 km away, was scanning. The volume nearest the first event began at 22:18 UTC.
1 flash flood. Local standard time, as filed.
Sunrise Beach Road between General's Highway and Old Herald Harbor Road was closed due to flooding. COOP Observer near the area reported 2.75 inches of rain around an hour.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2009Every state in 2009This day in weather historyWarnings in Maryland, September 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: 191921.