Special Weather Statement, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
236 PM EDT TUE JUL 19 2011

.SYNOPSIS...
A WEAK BOUNDARY WILL SLOWLY PUSH SOUTH ACROSS THE MID ATLANTIC
REGION THROUGH WEDNESDAY. STRONG HIGH PRESSURE ALOFT WILL BUILD FOR
THE LATTER HALF OF THE WEEK...LEADING TO HOT AND HUMID CONDTIONS.

&&

.NEAR TERM /THROUGH TONIGHT/...
WEAK FRONTAL BOUNDARY STILL DRAPED FROM CENTRAL OHIO THROUGH CENTRAL
PA THIS AFTERNOON. LEE TROUGH REMAINS SITUATED ACROSS THE EASTERN
CWFA. EARLIER MCS ACTIVITY HAS WEAKENED AND IS NOW ACROSS SW
VIRGINIA...BUT CONSIDERABLE CLOUD COVER CONTINUES ACROSS MOST OF THE
CWFA. VISIBLE SATELLITE IMAGERY SHOWS BREAKS IN THE CLOUD COVER
ACROSS THE NE...WHERE A GOOD CU FIELD HAS DEVELOPED ALONG WITH
SCATTERED SHOWERS AND THUNDERSTORMS.

MODIFIED 12Z SOUNDING SHOWED GOOD SURFACE INSTABILITY...WITH A NICE
INVERTED V STRUCTURE. CONVECTION SHOULD CONTINUE TO FORM ALONG ANY
MESOSCALE BOUNDARIES AND DIFFERENTIAL HEATING BOUNDARIES. DAMAGING
WIND GUSTS SHOULD BE THE PRIMARY THREAT FROM ANY SEVERE
THUNDERSTORMS THAT DEVELOP...ALONG WITH LOCALLY HEAVY RAINFALL. DO
EXPECT CONVECTION COVERAGE TO DIMINISH WITH THE LOSS OF HEATING.

WEAK FRONT WILL CONTINUE TO SLOWLY PUSH SOUTH THROUGH
TOMORROW...WITH HIGH PRESSURE BUILDING BEHIND THE BOUNDARY. AT THIS
POINT...NOT MUCH FORCING ALONG THE BOUNDARY AND CONVECTION SHOULD BE
LIMITED TO THE HIGHER TERRAIN.

TEMPS IN THE MID 90S WITH HEAT INDICES NEAR 100 EXPECTED ACROSS MUCH
OF THE AREA ON WEDNESDAY.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
A STRONG UPPER LEVEL RIDGE IS STILL EXPECTED TO GRADUALLY INTENSIFY
OVER THE CENTRAL CONUS THROUGH FRIDAY. THIS WILL HELP TO KEEP A VERY
WARM AND MOIST AIRMASS IN PLACE OVER THE REGION DURING THIS TIME.
ALOFT...PREVAILING NORTHWESTERLY FLOW WILL HELP MOVE SEVERAL WEAK
SHORTWAVES ACROSS THE CWA INTO THE WEEKEND. THESE SHORTWAVES SHOULD
ALLOW FOR SUFFICIENT LIFT TO HELP TRIGGER SHOWERS AND THUNDERSTORMS
EACH AFTERNOON. THE BEST CHANCE FOR PRECIPITATION APPEARS TO BE
FRIDAY AFTERNOON WITH MAX HEATING AS A SURFACE BOUNDARY SAGS
SOUTHWARD ACROSS THE MASON-DIXON LINE. TEMPERATURES AND HUMIDITY
WILL CERTAINLY BE HIGH ENOUGH TO PROVIDE A FAVORABLE ENVIRONMENT FOR
STORMS. AREAS ALONG THE MD/PA BORDER SOUTH TO THE BALTIMORE METRO
AREA SHOULD SEE THE MOST ACTIVITY.

HOWEVER...THE BIGGEST CONCERN FOR THE SHORT TERM ARE FORECASTED HIGH
HEAT INDICES. BY THURSDAY...MAX TEMPS SHOULD REACH INTO THE UPPER
90S AND LOWER 100S. MAX TEMPS FRIDAY WILL TOP OFF IN THE LOWER 100S
ACROSS MANY LOCATIONS. HEAT INDICES AROUND 110 ARE POSSIBLE THURSDAY
AND EVEN HOTTER CONDITIONS ARE EXPECTED FRIDAY WITH HEAT INDICES UP
TO 115 DEGREES. AN EXCESSIVE HEAT WATCH HAS BEEN ISSUED FOR THURSDAY
AFTERNOON AND EVENING...AND WILL LIKELY BE WARRANTED FOR FRIDAY.
THERE WILL BE LITTLE RELIEF FROM THE HEAT AT NIGHT WITH MIN TEMPS
RANGING FROM THE MID 70S TO LOW 80S...HIGHEST TEMPS EXPECTED TO BE
IN THE METRO AREAS.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
THE DANGEROUS HEAT WAVE WILL CONTINUE THROUGH THE DAY SATURDAY WITH
THE UPPER LEVEL RIDGE WILL BEGIN TO BREAK DOWN SATURDAY NIGHT. HEAT
HEADLINES WILL LIKELY BE NEEDED FOR THE BEGINNING OF THE WEEKEND. A
STRONGER SHORTWAVE WILL APPROACH THE AREA SATURDAY NIGHT HELPING
SUNDAY AND MONDAYS TEMPS TO BE A BIT MORE MILD. A CANADIAN HIGH
PRESSURE SYSTEM MAY START TO BUILD IN FROM THE NORTHWEST AT THE
BEGINNING OF THE WORK WEEK.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
SCATTERED TSRA POSSIBLE THIS AFTERNOON ACROSS THE NORTHEAST TERMINAL
SITES. CONVECTION SHOULD DIMINISH WITH THE LOSS OF HEATING THIS
EVENING. PATCHY MVFR FOG EXPECTED TOWARDS SUNRISE. NO CIG/VSBY
RESTRICTIONS ANTICIPATED ON WEDNESDAY.

MOSTLY VFR CONDITIONS EXPECTED THURSDAY THROUGH SATURDAY. SOME
SHOWERS AND THUNDERSTORMS COULD LOCALLY REDUCE VISIBILITIES IN THE
AFTERNOONS WITH PREVAILING LIGHT NORTHWESTERLY FLOW OVER THE CWA.

&&

.MARINE...
WEAK BOUNDARY TO PUSH SOUTH ACROSS THE WATERS THROUGH TOMORROW. HIGH
PRESSURE BUILDS BEHIND THE FRONT. NO HEADLINES ANTICIPATED...AS FLOW
REMAINS AOB 10 KT.

NO MARINE HEADLINES ARE EXPECTED FROM THURSDAY THROUGH THE WEEKEND.
A WEAK BOUNDARY WILL MOVE ACROSS THE WATERS FRIDAY AFTERNOON WITH
THE POTENTIAL FOR ISOLATED/SCATTERED SHOWERS AND THUNDERSTORMS OVER
NORTHERN PORTIONS OF THE CHESAPEAKE BAY.

&&

.CLIMATE...
HOT AND HUMID CONDITIONS ARE EXPECTED ACROSS THE REGION THIS WEEK.
RECORDS MAY BE MET AT BWI DCA AND IAD THURSDAY THROUGH SATURDAY.

RECORD HIGH TEMPERATURES

      THU       FRI       SAT
BWI   104 1930  101 1957  102 1991
DCA   104 1926  103 1926  101 1991
IAD   101 1991  98  1998  99  1991

RECORD HIGH MINIMUM TEMPERATURES

       THU      FRI      SAT
BWI    83 1930  81 1885  79 1978
DCA    82 1987  81 1987  81 1978
IAD    77 1987  75 1994  73 1978

&&

.EQUIPMENT...
THE NWR TRANSMITTER AT FROSTBURG IS CURRENTLY OFFLINE OWING TO
SCHEDULED MAINTENANCE ON THE TELEPHONE LINE CIRCUIT. PENDING
COMPLICATIONS...THE TELEPHONE COMPANY BELIEVES THE CIRCUIT WILL BE
OPERATIONAL BY 6AM...AT WHICH TIME THE BROADCAST WILL RESUME.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...EXCESSIVE HEAT WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY
     EVENING FOR DCZ001.
MD...EXCESSIVE HEAT WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY
     EVENING FOR MDZ003>007-009>011-013-014-016>018.
VA...EXCESSIVE HEAT WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY
     EVENING FOR VAZ025>031-036>040-042-050>057-501-502.
WV...EXCESSIVE HEAT WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY
     EVENING FOR WVZ051>053.
MARINE...NONE.

&&

LISTEMAA/LASORSA/LARSEN/SHEFFIELD

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
557 PM EDT TUE JUL 19 2011

MDZ003-004-WVZ053-192245-
WASHINGTON MD-FREDERICK MD-JEFFERSON WV-
557 PM EDT TUE JUL 19 2011

...STRONG THUNDERSTORM TO AFFECT WASHINGTON...FREDERICK AND JEFFERSON
COUNTIES...

AT 557 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 2 MILES
NORTHWEST OF BOONSBORO...MOVING SOUTH AT 20 MPH.

LOCATIONS IMPACTED INCLUDE ROHERSVILLE...ROHRERSVILLE...ANTIETAM...
GAPLAND...BROWNSVILLE AND PLEASANTVILLE.

STORM INTENSITY IS INCREASING...AND SEVERE WEATHER MAY DEVELOP
RAPIDLY. REMAIN ALERT...AND BE PREPARED TO TAKE ACTION IF WARNINGS
ARE ISSUED.

HEAVY RAIN WITH THIS STORM WILL REDUCE VISIBILITIES TO BELOW ONE MILE
AND MAY CAUSE PONDING OF WATER ON ROADWAYS.

WIND GUSTS IN EXCESS OF 50 MPH AND SMALL HAIL CAN BE EXPECTED WITH
THIS STORM. WINDS THIS STRONG CAN BRING DOWN LARGE TREE BRANCHES.
TAKE SHELTER UNTIL THE STORM HAS PASSED.

&&

LAT...LON 3932 7755 3933 7781 3958 7777 3958 7760
TIME...MOT...LOC 2157Z 002DEG 19KT 3951 7768

HTS

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