Upper-level high pressure provided enough subsidence for hot conditions on the 29th. A southerly flow around surface high pressure over the Atlantic caused humid conditions.
Every event with a place to put it; 5 filed by county or forecast zone are drawn at its center, in a lighter ring. 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.
Upper-level high pressure provided enough subsidence for hot conditions on the 29th. A southerly flow around surface high pressure over the Atlantic caused humid conditions. Hot and humid conditions caused heat indices over 105 degrees across many locations.
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 Jul 29, 10:36 AM EST, 24 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1136 AM EDT FRI JUL 29 2011
.SYNOPSIS...
HEAT AND HUMIDITY WILL BE COMMON TODAY AS UPPER HIGH PRESSURE
BUILDS OVER THE CAROLINAS. A WEAK COLD FRONT WILL PASS THROUGH
THE REGION LATE TONIGHT AND SATURDAY. HIGH PRESSURE WILL BUILD
OVER THE REGION EARLY NEXT WEEK.
&&
.NEAR TERM /THROUGH SATURDAY/...
UPDATE TO ADD CLIMATE SECTION BELOW.
PREV DISCUSSION....
TEMPS FCSTD TO CLIMB INTO UPR 90S- LWR 100S TDA AS H8 TEMPS EXCEED
22C. DRY LYR ABV SFC SHUD AID IN DECRG DEWPT TEMPS AS THE DP
MIXING ENSUES...EFFECTIVELY LMTG HEAT INDICES INTO SOLID ADZY
RANGE. CURRENT ADZY WILL CONT EXCEPT FOR AUGUSTA AND ALLEGANY
CTYS...WHERE LOW-LVL DRY AIR MIXING TO SFC WILL RESTRICT HEAT
INDICES TO BLW 105F.
DP MIXING ALSO WILL LEAD TO STEEP LOW-LVL LAPSE RATES. AS MID-LVL
SHRTWV TROF OVER ERN GRTLKS MOVES EWD AND ASSOCIATED CDFNT SLIDES
SWD SLOWLY THIS AFTN...H5 COLD AIR ADVCTN WILL STEEPEN MID-LVL
LAPSE RATES ALSO. RESULT WILL BE 1.5-2.5 KJ/KG CAPE ALONG AND
AHEAD OF CDFNT AT HIGHER ELEVATIONS WITH MINIMAL INHIBITION. SHEAR
IS NOT SPECTACULAR...BUT UPDRAFTS MAY BCM MODESTLY ORGANIZED. SVR
THREAT WILL BE DMGG WIND GUSTS.
CDFNT WILL MOVE SWD THRU FCST AREA TNGT BUT WILL SLOW AS IT DOES
SO AS ITS UPPER SUPPORT WANES. BNDRY SHUD BE LOCATED IN SWRN ZONES
BY SAT...WHERE FOCUS FOR RENEWED CNVCTV DVLPMT WILL BE BY SAT AFTN.
MAXIMA WILL BE ONLY SLGTLY ABV NRML...IN LOW-MID 90S.
&&
.SHORT TERM /SATURDAY NIGHT/...
SHWRS AND TSTMS MAY CONT SAT NGT IN SWRN PORTION OF FCST AREA.
MINIMA WILL BE IN THE 70S OWING TO CONTD LOW-LVL MSTR.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
UPPER RDG LOOKS TO BE RETROGADING DURG THE 1ST PART OF THE NEW
WK...WHICH IS UNFORTUNATE FOR PARCHED AND SCORCHING SRN PLAINS. IN
THE MID ATLC DAYTIME TEMPS SHOULD REACH LM90S EACH AFTN. ONLY
SAVING GRACE IS THAT THE INDUCED TROF ALONG THE ERN SEABOARD
SHOULD LOWER DWPTS TO THE M60S...PRBLY ALLEVIATING THE MID ATLC FM
NEEDING HEAT ADVISORIES. BUT W/ ALL THE HEAT THE CITIES HAS STORED
LOW TEMPS IN BALT/DC WL RMN IN THE U70S.
WE ARE LOSING DAYLIGHT - SO HIGH TEMPS WL DROP BLO 90 SOONER OR
LATER. ON 8/1 DAYLGT HRS ARE 14:10. RGN LOSES 7 MINUTES BY 8/4.
&&
.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
WITH DP WLY FLOW...DEWPTS SHUD DECR SOMEWHAT TDA. DOWNSLOPING FLOW
SHUD SUPPRESS A WDSPRD CU FIELD EXCEPT ON HIGHER TERRAIN. STRONG
HEATING WILL LEAD TO DP MIXING AND GUSTY WINDS TO 15 KT THIS AFTN.
TSTMS XPCD TO FORM ALONG CDFNT FROM WRN MD TO SRN PA AND SHUD MOVE
ESEWD TWD KMRB LATE THIS AFTN. CVRG MAY INCR SLGTLY THIS EVE AS
THE BNDRY APRCHS...BUT THE TSTMS WILL WANE AS IT INVADES A MORE
STABLE AMS. BEST CHCS FOR CNVCTN NEAR TERMINALS WILL BE KMRB/KIAD/
KBWI AND KMTN.
NLY WINDS XPCD LATE TNGT IN WAKE OF CDFNT. BNDRY WILL STALL OVER
CNTRL SHENANDOAH VLY ON SAT...LEADING TO CNVCTV POTENTIAL VCTY
KCHO BY SAT AFTN. VFR CONDS XPCTD TO CONT THRU THE WKND.
&&
.MARINE...
SFC TROF WILL RMN NEAR WATERS TDA. WLY WINDS SHUD BE COMMON WITH
GUSTS LMTD BY SHALLOW MIXING OVER RELATIVELY COOL WATERS. CDFNT
WILL MOVE ACRS WATERS TNGT AND MAY FOCUS TSTMS OVER NRN PORTIONS
OF THE MD CHSPK BAY.
WINDS COULD INCRS TO ARND 15 KT FOR SUNDAY...BUT NOT FORESEEING
NEED FOR AN SCA AT THIS TIME.
&&
.CLIMATE...
TEMPERATURES WILL LIKELY TIE OR BREAK DAILY RECORD MAX TEMPS TODAY
AT DCA/BWI/IAD. ALSO...THE MIN TEMP SO FAR TODAY AT DCA WAS 80F...
WHICH WOULD TIE ITS DAILY RECORD HIGH MIN IF THE TEMP DOES NOT DROP
BELOW 80F BEFORE MIDNIGHT LST. BELOW IS A LIST OF THE CLIMATE
RECORDS IN JEOPARDY OF BEING BROKEN...
TODAY...7/29...
RECORD MAX RECORD HIGH MIN
DCA....99F IN 1993 80F IN 1949
BWI....99F IN 1954
IAD....97F IN 1993
THE MIN TEMPERATURE WILL ALSO APPROACH DAILY RECORD HIGH MIN TEMPS
FOR SAT.
TOMORROW...7/30...
RECORD HIGH MIN
DCA....78F IN 2002/2008
BWI....78F IN 1901/1933
IAD....75F IN 1963
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...HEAT ADVISORY UNTIL 9 PM EDT THIS EVENING FOR DCZ001.
MD...HEAT ADVISORY UNTIL 9 PM EDT THIS EVENING FOR MDZ003>007-
009>011-013-014-016>018.
VA...HEAT ADVISORY UNTIL 9 PM EDT THIS EVENING FOR VAZ026>031-
036>040-042-050>057-501-502.
WV...HEAT ADVISORY UNTIL 9 PM EDT THIS EVENING FOR WVZ052-053.
MARINE...NONE.
&&
UPDATE...KRAMAR
CLIMATE...KLEIN
PREV DISCUSSION...LASORSA/WOODY!HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 947 AM EDT FRI JUL 29 2011 ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057- 301000- 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- 947 AM EDT FRI JUL 29 2011 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 A HEAT ADVISORY IS IN EFFECT FROM 11 AM UNTIL 9 PM. REFER TO THE LATEST HAZARD MESSAGE /NPWLWX/ FOR DETAILS. SCATTERED THUNDERSTORMS ARE POSSIBLE THIS EVENING IN NORTHERN MARYLAND. A FEW THUNDERSTORMS COULD PRODUCE DAMAGING WIND GUSTS. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .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>506-301000- 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- 947 AM EDT FRI JUL 29 2011 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 A HEAT ADVISORY IS IN EFFECT FROM 11 AM UNTIL 9 PM FOR COUNTIES ALONG AND EAST OF THE SHENANDOAH VALLEY. REFER TO THE LATEST HAZARD MESSAGE /NPWLWX/ FOR DETAILS. SCATTERED THUNDERSTORMS ARE POSSIBLE THIS EVENING IN NORTHERN MARYLAND...EASTERN WEST VIRGINIA AND EXTREME NORTHERN VIRGINIA. SOME THUNDERSTORMS COULD PRODUCE DAMAGING WIND GUSTS. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING. KRAMAR
The national radar mosaic for the moment the first event began.
6 heat. Local standard time, as filed.
Heat indices up to 105 degrees were measured the Andrews Air Force Base.
Heat indices up to 109 degrees were measured at the Maryland Science Center.
Heat indices up to 108 degrees were measured at Patuxent River.
Heat indices in excess of 105 degrees were estimated due to observations nearby.
Heat indices in excess of 105 degrees were estimated due to observations nearby.
Heat indices in excess of 105 degrees were estimated due to observations nearby.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2011Every state in 2011This day in weather historyWarnings in Maryland, July 2011
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: 338482, 338481, 338484, 338486, 338488, 338489.