Alert archive / Virginia / Flash Flood Warnings in 2012

Flash Flood Warning 76, NWS Baltimore/Washington

September 18, 2012Montgomery County, Prince George's County, Maryland; Arlington County, Fairfax County, City of Falls Church, Virginia

NWS Baltimore/Washington issued this flash flood warning at Sep 18, 2012, 2:50 PM EDT for Montgomery County, Prince George's County, Maryland; Arlington County, Fairfax County, City of Falls Church, Virginia. It was in force for 3 hr. 2 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Sep 18, 2012, 2:50 PM EDT (18:50 UTC)
Expired: Sep 18, 2012, 5:26 PM EDT
In force: 3 hr
Issued by: NWS Baltimore/Washington
Area: Storm-based polygon
Flood severity: None

Counties Montgomery County, MD, Prince George's County, MD, Arlington County, VA, City of Falls Church, VA, Fairfax County, VA

The radar

The Sterling radar (KLWX), 27 km from the middle of the area, began a volume at 18:50 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What was reported inside it

Time	Report	Where	Remark
Sep 18, 3:43 PM EDT	FLASH FLOOD	1 Wnw Rockville, MD	I-270 NORTH REPORTED FLOODED JUST NORTH OF THE MONTGOMERY AVENUE EXIT
Sep 18, 4:30 PM EDT	FLASH FLOOD	Chevy Chase View, MD	CONNECTICUT AVENUE REPORTED TO BE FLOODED AT SAUL ROAD.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

Did it verify

Verified. The Iowa Environmental Mesonet's Cow matched 2 storm reports to this flash flood warning; the first came 53 minutes after it went out.

Cow counts a report within 15 km of the polygon while the warning was in force: a tornado for a tornado warning; hail of 1 inch or more, a gust of 58 mph or more or wind damage for a severe thunderstorm warning; a flash flood report for a flash flood warning.

The nearest sounding before it

Washington/Dulle, VA (KIAD), launched 12:00Z, 6.8 hours before the alert went out and 20 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 371 J/kg
Mixed-layer CIN: 0 J/kg
Mixed-layer LCL: 454 m above ground
0-6 km bulk shear: 56 kt
0-1 km storm-relative helicity: 322 m²/s²
0-3 km storm-relative helicity: 403 m²/s²
Significant tornado parameter: 0.9
Supercell composite: 4.2

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

305 
WGUS51 KLWX 181850
FFWLWX
DCC001-MDC031-033-VAC013-059-610-182145-
/O.NEW.KLWX.FF.W.0076.120918T1850Z-120918T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
250 PM EDT TUE SEP 18 2012

THE NATIONAL WEATHER SERVICE IN STERLING VIRGINIA HAS ISSUED A

* FLASH FLOOD WARNING FOR...
  THE DISTRICT OF COLUMBIA...
  MONTGOMERY COUNTY IN CENTRAL MARYLAND...
  CITY OF FALLS CHURCH IN NORTHERN VIRGINIA...
  ARLINGTON COUNTY IN NORTHERN VIRGINIA...
  NORTHWESTERN PRINCE GEORGES COUNTY IN CENTRAL MARYLAND...
  NORTHERN FAIRFAX COUNTY IN NORTHERN VIRGINIA...

* UNTIL 545 PM EDT

* AT 246 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED   
  VERY HEAVY RAIN CAPABLE OF PRODUCING FLASH FLOODING. RADAR  
  ESTIMATES THAT ADDITIONAL RAINFALL AMOUNTS OF UP TO 2 INCHES       
  CAN BE EXPECTED. AN INCH OF RAIN MAY FALL IN AS LITTLE AS          
  15 MINUTES...WHICH WILL RAPIDLY CAUSE PONDING OF WATER ON          
  ROADWAYS. ADDITIONAL RAIN WOULD LEAD TO FLASH FLOODING.

* SOME LOCATIONS THAT ARE AFFECTED BY THE HEAVY RAIN INCLUDE
  ARLINGTON...BALLSTON...CHANTILLY...FALLS CHURCH...GREAT FALLS...   
  HERNDON...MCLEAN...RESTON...ROSSLYN...TYSONS CORNER...VIENNA...    
  BETHESDA...CHEVY CHASE...COLESVILLE...GAITHERSBURG...              
  GERMANTOWN...OLNEY...POTOMAC...ROCKVILLE...TAKOMA PARK...          
  ANACOSTIA...GEORGETOWN...DOWNTOWN WASHINGTON.

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLASH FLOODING OF
SMALL CREEKS AND STREAMS...URBAN AREAS...HIGHWAYS...STREETS...
UNDERPASSES AND OTHER DRAINAGE AREAS AND LOW LYING SPOTS.

LAT...LON 3904 7695 3896 7700 3889 7691 3886 7696
      3886 7727 3887 7729 3886 7731 3887 7742
      3894 7744 3906 7733 3914 7736 3926 7709

$$

JE

2 follow-up statements

902 
WGUS71 KLWX 182025
FFSLWX

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
425 PM EDT TUE SEP 18 2012

DCC001-MDC033-VAC013-059-610-182034-
/O.CAN.KLWX.FF.W.0076.000000T0000Z-120918T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
CITY OF FALLS CHURCH VA-ARLINGTON VA-DISTRICT OF COLUMBIA DC-
PRINCE GEORGES MD-FAIRFAX VA-
425 PM EDT TUE SEP 18 2012

...THE FLASH FLOOD WARNING HAS BEEN CANCELLED FOR DISTRICT OF
COLUMBIA...AND NORTHERN FAIRFAX...NORTHWESTERN PRINCE GEORGES...
ARLINGTON AND CITY OF FALLS CHURCH COUNTIES...

RAIN HAS MOVED OUT OF THE AREA...AND THE THREAT OF FLASH FLOODING 
HAS ENDED. THEREFORE...THE WARNING HAS BEEN CANCELLED.

LAT...LON 3926 7709 3904 7695 3896 7700 3900 7704
      3893 7712 3897 7715 3897 7720 3899 7725
      3900 7726 3903 7724 3906 7733 3914 7736

$$

MDC031-182145-
/O.CON.KLWX.FF.W.0076.000000T0000Z-120918T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
MONTGOMERY MD-
425 PM EDT TUE SEP 18 2012

...A FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 545 PM EDT FOR
MONTGOMERY COUNTY...

AT 418 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED 
RAINFALL WAS ENDING IN MONTGOMERY COUNTY. RADAR ESTIMATES THAT UP TO 
2 INCHES OF RAIN HAVE ALREADY FALLEN ACROSS PORTIONS OF THE COUNTY. 
ADDITIONAL RAINFALL AMOUNTS SHOULD BE LIGHT. SOME RESIDUAL URBAN 
FLOODING WILL CONTINUE FOR THE NEXT HOUR OR SO.

LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO ASPEN HILL...
BETHESDA...CHEVY CHASE...COLESVILLE...GAITHERSBURG...GERMANTOWN...
HILLANDALE...MONTGOMERY VILLAGE...NORTH POTOMAC...OLNEY...POTOMAC... 
ROCKVILLE...AND TAKOMA PARK.

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLASH FLOODING OF
SMALL CREEKS AND STREAMS...URBAN AREAS...HIGHWAYS...STREETS...
UNDERPASSES AND OTHER DRAINAGE AREAS AND LOW LYING SPOTS.

LAT...LON 3926 7709 3904 7695 3896 7700 3900 7704
      3893 7712 3897 7715 3897 7720 3899 7725
      3900 7726 3903 7724 3906 7733 3914 7736

$$

JE

204 
WGUS71 KLWX 182126
FFSLWX

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
526 PM EDT TUE SEP 18 2012

MDC031-182136-
/O.CAN.KLWX.FF.W.0076.000000T0000Z-120918T2145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
MONTGOMERY MD-
526 PM EDT TUE SEP 18 2012

...THE FLASH FLOOD WARNING HAS BEEN CANCELLED FOR MONTGOMERY
COUNTY...

RAIN HAS DIMINISHED AND STREAMS HAVE CRESTED...THEREFORE THE FLASH 
FLOOD WARNING HAS BEEN CANCELLED.

LAT...LON 3926 7709 3904 7695 3896 7700 3900 7704
      3893 7712 3897 7715 3897 7720 3899 7725
      3900 7726 3903 7724 3906 7733 3914 7736

$$

JE

What forecasters said that day

The local office's own words before this flash flood warning went out, 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 this flash flood warning went out at Sep 18, 2:01 PM EDT, 49 minutes earlier.

Area forecast discussion, Sep 18, 2:01 PM EDT, 49 minutes before

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
201 PM EDT TUE SEP 18 2012

.SYNOPSIS...
A STRONG COLD FRONT WILL PASS THROUGH THE AREA LATE THIS AFTERNOON
AND EVENING. HIGH PRESSURE WILL BUILD IN DURING THE MID TO LATE
PORTION OF THE WEEK. ANOTHER SYSTEM COULD BRING INCLEMENT WEATHER
OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
UPDATE...
FLASH FLOOD WATCH NOW IN EFFECT - THROUGH 8 PM...IN ADDITION TO THE
TORNADO WATCH STILL IN EFFECT - THROUGH 7 PM. THE FLASH FLOOD
WATCH IN EFFECT FOR THE SAME AREAS AS THE TORNADO WATCH...THE
SHENANDOAH VLY AND EASTWARD.

FROM PREV DISC...
INTENSE LOW LEVEL JET DEVELOPING OVER THE AREA...DRIVING STRONG
LOW LEVEL FLOW - CREATING LINE SEGMENTS OF SHOWER ACTIVITY W/
LOCALLY STRONG-TO-DAMAGING WINDS. INSTABILITY IS FAIRLY
WEAK...WHICH IS KEEPING MUCH OF THIS ACTIVITY AS HEAVY SHOWERS W/
NO LIGHTNING AS OF YET. SOME PERIODIC BREAKS OVER THE NEXT FEW HRS
WILL CHANGE THAT...ESPECIALLY ACROSS THE SRN HALF OF THE CWA.

CURRENTLY...A FEW LINE SEGMENTS GATHERING THEMSELVES OVER THE NRN
SHENANDOAH VLY AND SLIDING NEWD. LOCALIZED DOWNBURST WINDS
EXPECTED IN THE MORE BOWED-OUT ACTIVITY. A GENERAL 25-35MPH BREEZE
OUT OF THE SOUTH HAS DEVELOPED OUT AHEAD OF THIS ACTIVITY AND
SPREAD OVER MUCH OF THE PIEDMONT. THESE ARE ENVIRONMENTAL WINDS
AND THESE WINDS WILL CONTINUE UNTIL THE FRONT MOVES THRU LATER
TODAY.

COASTAL FLOOD WATCH CONVERTED TO A CF WARNING FOR ANNE AR-SRN
BALT- HARFORD CO'S FOR THE LATE NIGHT H.T. CYCLE. STRONG GUSTY
WINDS - GALE FORCE FOR THE NEXT SEVERAL HRS - WILL DEVELOP WATER
LEVELS AROUND 2 FT ABOVE NORMAL LEADING TO MODERATE CF AT HIGH
TIDE. SEE WBCCFWLWX FOR FURTHER DETAILS.

THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON AND EVENING AS
THE COLD FRONT APPROACHES FROM THE WEST. SHORT RANGE MODELS ARE
SHOWING A QLCS LINE DEVELOPING AHEAD OF THE COLD FRONT AND MOVING
EAST ACROSS THE CWFA. DO THINK THE HIGHEST POTENTIAL FOR SEVERE
WEATHER WILL BE ALONG AND EAST OF THE SHENANDOAH VALLEY THIS
AFTERNOON AND EVENING WITH THE QLCS LINE. A COUPLE OF THINGS TO
NOTE...THERE IS NOT MUCH FORCING IN THE MID LEVELS AND THE 500MB
TROUGH REMAINS NEUTRAL. HOWEVER...WITH MUCH OF THE CWFA EAST OF THE
SHENANDOAH VALLEY IN THE WARM SECTOR...SB CAPE IS EXPECTED TO
INCREASE TO BETWEEN 1000 AND 2000 J/KG. IN ADDITION...HODOGRAPHS
SHOW A GOOD POSSIBILITY OF ROTATING THUNDERSTORMS.

FOR THE AFTERNOON AND EVENING HOURS...MAINLY ALONG AND EAST OF THE
SHENANDOAH VALLEY...THUNDERSTORMS WILL HAVE THE POTENTIAL TO BECOME
SEVERE PRODUCING DAMAGING WIND GUSTS. A FEW TORNADOES ARE POSSIBLE.
THUNDERSTORMS WILL ALSO BE CAPABLE OF PRODUCING LOCALLY HEAVY
RAINFALL...WITH LOCALIZED FLASH FLOODING.

FRONT SHOULD CLEAR THE BAY DURING THE LATE EVENING HOURS. HIGH
PRESSURE WILL BUILD IN FROM THE WEST...WITH A GRADUAL CLEARING OF
SKIES.

GRADIENT IS EXPECTED TO TIGHTEN TODAY AS LOW PRESSURE
APPROACHES...AND HAVE UPPED THE WIND GUST POTENTIAL ACROSS THE LAND
A FEW KT/MPH. POPS LOOKED GOOD...AND MADE NO CHANGES PAST 12Z. TOOK
BLEND FOR TEMPS.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AN UPPER-LEVEL TROUGH WILL REMAIN TO OUR WEST STRETCHING FROM THE
GREAT LAKES SOUTH INTO THE GULF COAST STATES WHILE SURFACE HIGH
PRESSURE APPROACHES THE AREA WEDNESDAY BEFORE BUILDING OVERHEAD
WEDNESDAY NIGHT INTO THURSDAY.

DESPITE A SOUTHWEST FLOW ALOFT AHEAD OF THE TROUGH...SUBSIDENCE FROM
THE SURFACE HIGH ALONG WITH LOW-LEVEL DRY AIR SHOULD KEEP MOST
CLOUDS AND PRECIPITATION WELL OFF TO OUR SOUTHEAST. A NORTHERLY
SURFACE FLOW AHEAD OF THE HIGH WEDNESDAY WILL ALLOW FOR MAX TEMPS TO
BE BELOW NORMAL...DESPITE SUNSHINE. MAX TEMPS WILL RANGE FROM NEAR
60 IN THE MOUNTAINS TO THE LOWER AND MIDDLE 70S ACROSS MOST OTHER
LOCATIONS.

DRY AND CHILLY CONDITIONS ARE EXPECTED WEDNESDAY NIGHT AS HIGH
PRESSURE BUILDS OVERHEAD. MAINLY CLEAR SKIES AND LIGHT WINDS WILL
CAUSE RADIATIONAL COOLING. MIN TEMPS WILL RANGE FROM THE LOWER 40S
ACROSS MOST LOCATIONS IN THE POTOMAC HIGHLANDS AND SHENANDOAH
VALLEY...TO THE MIDDLE 40S IN THE SUBURBS OF
WASHINGTON/BALTIMORE...TO THE MIDDLE 50S IN DOWNTOWN
WASHINGTON/BALTIMORE.

HIGH PRESSURE WILL WEAKEN OVER THE AREA THURSDAY AND A RETURN FLOW
WILL DEVELOP...ALLOWING FOR MAX TEMPS TO BE CLOSER TO CLIMO. MORE
DRY CONDITIONS ARE EXPECTED ALONG WITH SUNSHINE.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
HIGH PRESSURE WILL CONTINUE TO WEAKEN AS IT SHIFTS OFF THE COAST
THURSDAY NIGHT THROUGH FRIDAY WHILE A COLD FRONT MOVES THROUGH THE
OHIO VALLEY. A RETURN FLOW WILL ALLOW FOR MAX TEMPS FRIDAY TO BE A
FEW DEGREES WARMER COMPARED TO THURSDAY. DRY CONDITIONS WILL LIKELY
PERSIST ALONG WITH SOME SUNSHINE AS THE FRONT REMAINS TO THE
WEST.

YET ANOTHER UPPER TROUGH WILL TAKE SHAPE OVER THE GREAT LAKES BY
SATURDAY. THIS SYSTEM IS PROGGED TO DEEPEN AND SHIFT EAST TOWARD
THE FORECAST AREA OVER THE WEEKEND. WILL CONTINUE TO SHOW
INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS ESPECIALLY
SATURDAY AFTERNOON INTO SATURDAY NIGHT WITH CLEARING SUNDAY
AFTERNOON. STILL SOME TIMING UNCERTAINTIES IN THE MODELS. HIGH
PRESSURE WILL RETURN FOR EARLY NEXT WEEK.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
A LINE OF STRONG TO SEVERE THUNDERSTORMS IS EXPECTED TO DEVELOP
THIS AFTERNOON AND MOVE EAST ACROSS THE MID ATLANTIC.

IFR CONDITIONS WILL CONTINUE AT MOST OF THE TAF SITES THROUGH
DAYBREAK...AS GIGS/VSBYS REMAIN LOW IN WIDESPREAD RAINFALL. CIGS MAY
INCREASE SLIGHTLY TO MVFR VALUES WITH SUNRISE. VSBYS WILL BE REDUCED
IN LOCALLY HEAVY RAINFALL/THUNDERSTORMS THIS AFTERNOON AND EVENING.

HIGH PRESSURE WILL BRING VFR CONDITIONS MOST OF THE TIME WEDNESDAY
THROUGH FRIDAY. PATCHY BR/FOG MAY REDUCE VSBYS DURING THE EARLY
MORNING HOURS EACH DAY. A COLD FRONT WILL PASS THROUGH THE TERMINALS
SATURDAY...BRINGING THE CHANCE FOR SHOWERS.

&&

.MARINE...
A COLD FRONT WILL CROSS THE WATERS TONIGHT. DURING THE
AFTERNOON/EVENING...A LINE OF SHOWERS AND THUNDERSTORMS WILL CROSS
THE WATERS AHEAD OF THE COLD FONT. SPECIAL MARINE WARNINGS ARE
POSSIBLE. WATERSPOUTS ARE ALSO A POSSIBILITY.

BEHIND THE FRONT...WINDS WILL DECREASE SLIGHTLY...BUT SMALL CRAFT
CONDITIONS WILL CONTINUE OVERNIGHT. A WIND SHIFT TO THE W/NW IS
EXPECTED LATE TONIGHT ACROSS THE WATERS.

A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS WEDNESDAY BEHIND
A COLD FRONT. HIGH PRESSURE WILL BUILD OVER THE WATERS WEDNESDAY
NIGHT INTO THURSDAY ALLOWING FOR WINDS TO DIMINISH. HIGH PRESSURE
WILL MOVE OFF THE COAST FRIDAY AND A COLD FRONT WILL IMPACT THE
WATERS DURING THE WEEKEND.

&&

.TIDES/COASTAL FLOODING...
ANOMALIES HAVE BEGUN TO INCREASE AS THE SOUTHERLY FLOW STRENGTHENS
EARLY THIS MORNING. A COASTAL FLOOD ADVISORY IS IN EFFECT FOR THE
MORNING/EARLY AFTERNOON HIGH TIDE FOR ANNE ARUNDEL COUNTY NORTHWARD
ALONG THE WESTERN SHORE OF THE CHESAPEAKE BAY AND ALSO FOR THE
CITIES OF WASHINGTON DC...ALEXANDRIA...AND THE COUNTIES OF PRINCE
GEORGES AND FAIRFAX ALONG THE TIDAL POTOMAC RIVER.

THE AFTERNOON/NIGHTTIME HIGH TIDE WILL LIKELY BE AFFECTED BY
THESE ANOMALIES. MODERATE FLOODING IS POSSIBLE ACROSS THESE
AREAS. A COASTAL FLOOD ADVISORY IS IN EFFECT FOR LOCATIONS ALONG
THE SHORE OF THE UPPER TIDAL POTOMAC RIVER.

ANOMALIES SHOULD DROP QUICKLY EARLY WEDNESDAY AS AN OFFSHORE FLOW
TAKES OVER BEHIND THE COLD FRONT.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR DCZ001.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR DCZ001.
MD...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR MDZ003>007-
     009>011-013-014-016>018.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR MDZ013.
     COASTAL FLOOD WARNING FROM 6 PM THIS EVENING TO 2 AM EDT
     WEDNESDAY FOR MDZ007-011-014.
     COASTAL FLOOD ADVISORY UNTIL 6 PM EDT THIS EVENING FOR MDZ007-
     011-014.
     COASTAL FLOOD ADVISORY UNTIL 10 PM EDT THIS EVENING FOR MDZ017-
     018.
VA...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR VAZ025>031-
     036>040-042-050>057-501-502.
     COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR VAZ053-
     054.
WV...FLASH FLOOD WATCH UNTIL 8 PM EDT THIS EVENING FOR WVZ051>053.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 5 PM EDT
     WEDNESDAY FOR ANZ530>532-535-536-538>540.
     GALE WARNING UNTIL 6 PM EDT THIS EVENING FOR ANZ530>532-535-
     536-538>540.
     SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 5 PM EDT
     WEDNESDAY FOR ANZ533-534-537-541>543.
     GALE WARNING UNTIL MIDNIGHT EDT TONIGHT FOR ANZ533-534-537-
     541>543.

&&

UPDATE...GMS
PREV DISCUSSION...LISTEMAA/LASORSA

Hazardous weather outlook, Sep 18, 2:03 PM EDT, 47 minutes before

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
203 PM EDT TUE SEP 18 2012

ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
191615-
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-
203 PM EDT TUE SEP 18 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 FLASH FLOOD WATCH IS IN EFFECT FOR MUCH OF EASTERN MARYLAND AND
NORTHERN VIRGINIA...INCLUDING THE WASHINGTON AND BALTIMORE
METROPOLITAN AREAS...THROUGH 8 PM. SEE WBCFFALWX FOR FURTHER
DETAILS.

TORNADO WATCH...NUMBER 642...IS IN EFFECT FOR MUCH OF EASTERN
MARYLAND AND NORTHERN VIRGINIA...INCLUDING THE WASHINGTON AND
BALTIMORE METROPOLITAN AREAS...THROUGH 7 PM. SEE WBCWCNLWX FOR
FURTHER DETAILS.

A GALE WARNING IS NOW IN EFFECT FOR THE WATERS THROUGH EARLY
EVENING. GALE CONDITIONS WILL CONTINUE FOR PORTIONS OF THE WATERS
THIS EVENING...WITH SMALL CRAFT CONDITIONS EXPECTED FOR ALL WATERS
OVERNIGHT.

SHOWERS AND THUNDERSTORMS ARE EXPECTED ALONG AND AHEAD OF A COLD
FRONT THROUGH THIS EVENING. HEAVY DOWNPOURS COULD LEAD TO
LOCALIZED FLASH FLOODING. IN ADDITION...SOME THUNDERSTORMS MAY BE
SEVERE AND PRODUCE DAMAGING WIND GUSTS AND ISOLATED TORNADOES. THE
MOST LIKELY TIME FOR SEVERE WEATHER LOOKS TO BE FROM 1 PM TO 7 PM.

A COASTAL FLOOD WARNING IS IN EFFECT FOR ANNE ARUNDEL...SOUTHERN
BALTIMORE AND HARFORD COUNTIES LATE THIS EVENING INTO THE EARLY
MORNING HOURS...FOR THE POTENTIAL OF MODERATE COASTAL FLOODING AT
HIGH TIDE. A COASTAL FLOOD ADVISORY REMAINS IN EFFECT FOR THE
WESTERN SHORE OF THE CHESAPEAKE BAY AND UPPER TIDAL POTOMAC RIVER
THROUGH LATE TONIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

A SMALL CRAFT ADVISORY IS IN EFFECT WEDNESDAY FOR THE WATERS.

.SPOTTER INFORMATION STATEMENT...

SKYWARN HAS BEEN ACTIVATED FOR THIS AFTERNOON AND EVENING. PLEASE
RELAY REPORTS OF SEVERE WEATHER AND/OR FLOODING TO YOUR LOCAL LAW
ENFORCEMENT AND THE NATIONAL WEATHER SERVICE.

MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504-
WVZ050>053-055-501>506-191615-
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-
203 PM EDT TUE SEP 18 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

A FLASH FLOOD WATCH IS IN EFFECT FOR MUCH OF WESTERN AND NORTHERN
MARYLAND...PORTIONS OF THE EASTERN WEST VIRGINIA PANHANDLE...AND
NORTHERN VIRGINIA THROUGH 8 PM. SEE WBCFFALWX FOR FURTHER DETAILS.

TORNADO WATCH NUMBER 642 IS IN EFFECT FOR MUCH OF WESTERN AND
NORTHERN MARYLAND...PORTIONS OF THE EASTERN WEST VIRGINIA
PANHANDLE...AND NORTHERN VIRGINIA THROUGH 7 PM. SEE WBCWCNLWX FOR
FURTHER DETAILS.

SHOWERS AND THUNDERSTORMS ARE EXPECTED ALONG AND AHEAD OF A COLD
FRONT TODAY. HEAVY DOWNPOURS COULD LEAD TO LOCALIZED FLASH FLOODING.
IN ADDITION...SOME THUNDERSTORMS MAY BE SEVERE AND PRODUCE
DAMAGING WIND GUSTS AND ISOLATED TORNADOES. THE MOST LIKELY TIME
FOR SEVERE WEATHER LOOKS TO BE FROM NOON TO 6 PM.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN HAS BEEN ACTIVATED FOR THIS AFTERNOON AND EVENING. PLEASE
RELAY REPORTS OF SEVERE WEATHER AND/OR FLOODING TO YOUR LOCAL LAW
ENFORCEMENT AND THE NATIONAL WEATHER SERVICE.

In the hours before

Local storm report, Sep 18, 1:52 PM EDT, 58 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
152 PM EDT TUE SEP 18 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0140 PM     FLASH FLOOD      1 SSW FREDERICK         39.41N  77.43W
09/18/2012                   FREDERICK          MD   PUBLIC

            12 TO 18 INCHES OF WATER COVERING THE ROAD NEAR WEST
            FREDERICK MIDDLE SCHOOL.

&&

EVENT NUMBER LWX1201239

JE

Local storm report, Sep 18, 2:01 PM EDT, 49 minutes before

PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
201 PM EDT TUE SEP 18 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0140 PM     FLASH FLOOD      1 SSW FREDERICK         39.41N  77.43W
09/18/2012                   FREDERICK          MD   PUBLIC

            12 TO 18 INCHES OF WATER COVERING PATRICK STREET NEAR
            WEST FREDERICK MIDDLE SCHOOL.

&&

CORRECTED REMARKS

EVENT NUMBER LWX1201239

JE

Local storm report, Sep 18, 2:20 PM EDT, 30 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
220 PM EDT TUE SEP 18 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0125 PM     FLASH FLOOD      1 W PURCELLVILLE        39.13N  77.74W
09/18/2012                   LOUDOUN            VA   TRAINED SPOTTER

            WATER COVERING ROADWAY ALONG TRANQUILITY ROAD

&&

EVENT NUMBER LWX1201240

KLW

Local storm report, Sep 18, 2:23 PM EDT, 27 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
223 PM EDT TUE SEP 18 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0125 PM     FLASH FLOOD      2 NNE PURCELLVILLE      39.16N  77.70W
09/18/2012                   LOUDOUN            VA   TRAINED SPOTTER

            WATER FLOWING AND COVERING BRIDGE ON ALLDER SCHOOL ROAD

&&

EVENT NUMBER LWX1201241

KLW

Local storm report, Sep 18, 2:36 PM EDT, 14 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
236 PM EDT TUE SEP 18 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0226 PM     FLASH FLOOD      1 ESE EMMITSBURG        39.70N  77.31W
09/18/2012                   FREDERICK          MD   DEPT OF HIGHWAYS

            INTERSECTION OF MD 140 AND HARNEY ROAD FLOODED AND
            CLOSED.

&&

EVENT NUMBER LWX1201242

JE

Local storm report, Sep 18, 2:39 PM EDT, 11 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
239 PM EDT TUE SEP 18 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0229 PM     FLASH FLOOD      2 NE MYERSVILLE         39.53N  77.54W
09/18/2012                   FREDERICK          MD   DEPT OF HIGHWAYS

            WOLFSVILLE ROAD FLOODED AND CLOSED AT CROW ROCK ROAD.

&&

EVENT NUMBER LWX1201243

JE

The office that day

Everything else NWS Baltimore/Washington issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 18, 1:34 AM EDT	Coastal Flood Advisory	LWX	Anne Arundel, Baltimore, Calvert, Charles, Prince George's, Saint Mary's and 1 more	23 hr
Sep 18, 9:20 AM EDT	Coastal Flood Warning	LWX	Anne Arundel, Baltimore, City of Baltimore	15 hr
Sep 18, 10:20 AM EDT	Special Weather Statement	LWX	Washington	40 min
Sep 18, 11:07 AM EDT	Special Weather Statement	LWX	Frederick	38 min
Sep 18, 11:13 AM EDT	Severe Thunderstorm Warning	LWX	Frederick, Washington	47 min
Sep 18, 11:39 AM EDT	Special Weather Statement	LWX	Carroll, Frederick	66 min
Sep 18, 12:19 PM EDT	Severe Thunderstorm Warning	LWX	Carroll, Frederick	41 min
Sep 18, 12:29 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Washington	61 min
Sep 18, 12:39 PM EDT	Flash Flood Warning	LWX	Carroll, Frederick, Washington	4 hr
Sep 18, 12:59 PM EDT	Flash Flood Warning	LWX	Frederick	3 hr
Sep 18, 1:02 PM EDT	Special Weather Statement	LWX	Saint Mary's	28 min
Sep 18, 1:10 PM EDT	Severe Thunderstorm Warning	LWX	Carroll, Frederick	54 min
Sep 18, 1:37 PM EDT	Special Weather Statement	LWX	Frederick	8 min
Sep 18, 1:54 PM EDT	Severe Thunderstorm Warning	LWX	Frederick, Montgomery	66 min
Sep 18, 1:56 PM EDT	Flash Flood Watch	LWX	Anne Arundel, Baltimore, Calvert, Carroll, Charles, Frederick and 4 more	4 hr
Sep 18, 2:18 PM EDT	Severe Thunderstorm Warning	LWX	Montgomery	57 min
Sep 18, 2:38 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Carroll, Frederick, Howard, Montgomery	52 min
Sep 18, 3:09 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Montgomery, Prince George's	66 min
Sep 18, 3:10 PM EDT	Special Weather Statement	LWX	Baltimore, Howard, City of Baltimore	35 min
Sep 18, 3:17 PM EDT	Tornado Warning	LWX	Montgomery, Prince George's	17 min
Sep 18, 3:24 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Baltimore, Carroll, Harford, Howard, Montgomery and 2 more	66 min
Sep 18, 3:25 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Calvert, Charles, Prince George's, Saint Mary's	65 min
Sep 18, 3:28 PM EDT	Flash Flood Warning	LWX	Baltimore, City of Baltimore	2 hr
Sep 18, 3:32 PM EDT	Severe Thunderstorm Warning	LWX	Baltimore, Harford	28 min
Sep 18, 3:39 PM EDT	Severe Thunderstorm Warning	LWX	Calvert, Charles, Saint Mary's	47 min
Sep 18, 3:53 PM EDT	Areal Flood Warning	LWX	Carroll, Frederick	20 hr
Sep 18, 4:15 PM EDT	Special Weather Statement	LWX	Anne Arundel	30 min
Sep 18, 4:22 PM EDT	Severe Thunderstorm Warning	LWX	Anne Arundel, Calvert	23 min
Sep 18, 4:29 PM EDT	Special Weather Statement	LWX	Saint Mary's	16 min
Sep 18, 4:55 PM EDT	Special Weather Statement	LWX	Saint Mary's	35 min
Sep 18, 5:27 PM EDT	Special Weather Statement	LWX	Saint Mary's	33 min
Sep 18, 4:26 AM EDT	Small Craft Advisory	LWX		35 hr
Sep 18, 8:08 AM EDT	Special Weather Statement	LWX	Highland	37 min
Sep 18, 9:25 AM EDT	Special Weather Statement	LWX	Frederick, Shenandoah	65 min
Sep 18, 10:19 AM EDT	Special Weather Statement	LWX	Clarke, Frederick, Warren, City of Winchester	41 min
Sep 18, 10:31 AM EDT	Severe Thunderstorm Warning	LWX	Clarke, Frederick, Page, Shenandoah, Warren, City of Winchester	44 min
Sep 18, 10:48 AM EDT	Special Weather Statement	LWX	Page, Rockingham, Shenandoah	42 min
Sep 18, 11:15 AM EDT	Severe Thunderstorm Warning	LWX	Frederick, Page, Shenandoah, Warren	45 min
Sep 18, 11:58 AM EDT	Special Weather Statement	LWX	Clarke, Warren	32 min
Sep 18, 12:04 PM EDT	Special Weather Statement	LWX	Warren	26 min
Sep 18, 12:26 PM EDT	Special Marine Warning	LWX		75 min
Sep 18, 12:40 PM EDT	Special Weather Statement	LWX	Albemarle, Nelson, City of Charlottesville	65 min
Sep 18, 12:45 PM EDT	Special Weather Statement	LWX	Clarke	15 min
Sep 18, 12:58 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, Greene, Nelson, Orange, City of Charlottesville	62 min
Sep 18, 1:06 PM EDT	Special Weather Statement	LWX	Greene, Loudoun, Madison, Rappahannock	54 min
Sep 18, 1:17 PM EDT	Flash Flood Warning	LWX	Clarke, Frederick, City of Winchester	101 min
Sep 18, 1:25 PM EDT	Severe Thunderstorm Warning	LWX	Albemarle, Culpeper, Fauquier, Greene, Madison, Orange and 2 more	65 min
Sep 18, 1:31 PM EDT	Special Weather Statement	LWX	Loudoun	29 min
Sep 18, 2:26 PM EDT	Special Marine Warning	LWX		94 min
Sep 18, 2:26 PM EDT	Severe Thunderstorm Warning	LWX	Culpeper, Fauquier, King George, Orange, Prince William, Spotsylvania and 2 more	64 min
Sep 18, 2:56 PM EDT	Areal Flood Warning	LWX	Clarke, Frederick, Shenandoah, Warren, City of Winchester	4 hr
Sep 18, 3:24 PM EDT	Special Marine Warning	LWX		81 min
Sep 18, 3:27 PM EDT	Special Marine Warning	LWX		60 min
Sep 18, 3:49 PM EDT	Special Marine Warning	LWX		86 min
Sep 18, 5:25 PM EDT	Special Marine Warning	LWX		108 min

Nearby

Flash Flood Warnings in Virginia, 2012 Flash Flood Warnings in Maryland, 2012 Flash Flood Warnings in District of Columbia, 2012 Every flash flood warning in 2012

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.