Tornado Warning 6, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1138 AM EDT WED JUL 29 2009

.SYNOPSIS...
A WARM AND MOIST AIR MASS WILL REMAIN OVER THE MID ATLANTIC OVER THE
NEXT SEVERAL DAYS. A FRONTAL BOUNDARY WILL REMAIN STALLED OUT OVER
THE AREA THROUGH THE WEEKEND...PROVIDING PERIODIC CHANCES OF SHOWERS
AND THUNDERSTORMS.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
EXTENSIVE CLD CVR LMTG HEATING ACRS MUCH OF FCST AREA. HOWEVER...
BKN CVR NOTED ACRS E-CNTRL VA...WHERE CU FIELD DVLPG ATTM. DECRG
CLD CVR RGN ADVCTG NEWD TWD SRN MD...AND XPCD TO DVLP NWD TO NEAR
BALTIMORE BY THIS AFTN.

ATMOSPHERE RMNS UNSTABLE IN THIS AREA...WHERE LWR LVLS STILL
EXHIBIT DECENT LAPSE RATES AS A RESULT OF ONLY MINIMAL CVRG OF
PCPN. STILL APPEARS TSTMS WILL DVLP THIS AREA...WITH GOOD INSTBY
AND INCRG LOW-LVL JET TO ENHANCE LOW-LVL SHEAR. WILL MAINTAIN
THREAT OF DMGG WINDS AND ISOLD TORNADOES...AND MENTION ISOLD HAIL.

GIVEN PWAT VALUE OF 1.84 ON MRNG RAOB...HVY RAIN RMNS A CONCERN.
ALTHO TSTMS WILL MOVE QUICKLY...XPC CVRG OF CNVCTN TO POSE A
LOCALIZED FLOOD THREAT.

ELSEWHERE...CLD CVR XPCD TO RMN IN PLACE...WITH CONTD WIDESPREAD
SHRA. THUS...MAXIMA SHUD RMN UPR 70S TO LWR 80S. PREV DISCUSSION
FOLLOWS...

ATMOSPHERE ACROSS THE CWA EARLY THIS MORNING WAS VERY MOIST AND
UNSTABLE. MESOANALYSIS INDICATED AN INSTABILITY AXIS OF MLCAPE
ALIGNED FROM CENTRAL VIRGINIA NORTHEAST INTO NORTH CENTRAL MARYLAND
AT 06Z...WITHIN A ZONE OF MOISTURE ADVECTION. NOCTURNAL CONVECTION
WAS FIRING ALONG THIS INSTABILITY AXIS AND THE ADVECTION ZONE AND
WILL PROGRESS NORTHEASTWARD THROUGH THE EARLY MORNING HOURS.

WITH HIGH PRESSURE ANCHORED OFF THE EASTERN SEABOARD /BERMUDA
HIGH/...A NEARLY ALIGNED SOUTH-SOUTHWEST FLOW WILL FEED DEEP
MOISTURE INTO AND THROUGH THE CWA TODAY. PRECIPITABLE WATER
VALUES OF AROUND 2 INCHES ACROSS NORTH CAROLINA AT 06Z WILL ADVECT
NORTHEASTWARD INTO THE CWA LATER THIS MORNING AND THIS AFTERNOON
AHEAD OF A STRONG SHORTWAVE OVER THE OHIO VALLEY. IN THE WAKE OF
THE AFOREMENTIONED EARLY MORNING CONVECTION...ADDITIONAL
CONVECTIVE ACTIVITY WILL MOVE NORTHEAST INTO THE CWA AND ALSO NEW
ACTIVITY WILL DEVELOP OVER THE CWA DURING THE LATE MORNING AND
AFTERNOON HOURS. POPS FROM 00Z MET MOS AND MAV MOS ARE
CATEGORICAL...WHICH IS SUPPORTED BY 21Z SREFS AND ALSO ADEQUATELY
INDICATES THE TEMPORAL/SPATIAL TRENDS FOR INCREASING POPS WHICH
DENOTES A NEAR 100 POP FOR MUCH OF THE CWA BY THIS AFTERNOON.

WITH PRECIPITABLE WATER VALUES INCREASING AOA 2.0 INCHES...THIS
WILL PLACE PORTIONS OF THE CWA NEAR 2 STANDARD DEVIATIONS ABOVE THE
NORMAL PRECIPITABLE WATER VALUE FOR LATE JULY. THEREFORE...EVEN
THOUGH STORM MOTION WILL BE ABLE TO MOVE CONVECTION...CONVECTION
WILL POSE A HEAVY RAINFALL THREAT ESPECIALLY DURING THE AFTERNOON
HOURS GIVEN THE HIGH PRECIPITABLE WATER ENVIRONMENT. ENHANCED
HEAVY RAINFALL WORDING HAS BEEN INCLUDED IN THE GRIDS AND WILL BE
MENTIONED IN THE HWO.

MOREOVER...DESPITE INITIAL CLOUDS AND CONVECTION...MODELS INDICATE
WEAK TO PERHAPS MODERATE AMOUNTS OF CAPE DURING THE AFTERNOON HOURS.
THIS FROM BOTH THE OPERATIONAL MODELS AND SREFS...AND AT THE SAME
TIME AS BULK SHEAR INCREASES AS A LOW LEVEL JET INTENSIFIES AHEAD OF
THE SHORTWAVE TROUGH. THEREFORE...IN ADDITION TO A HEAVY RAINFALL
THREAT...THERE WILL BE SEVERE WEATHER THREAT. 21Z SREFS COMBINED
PROBS FOR 1000 J/KG CAPE...30 KT SHEAR AND MEASURABLE PRECIP
INDICATES EAST TO THE BLUE RIDGE BEING THE MOST LIKELY AREA FOR
SEVERE WEATHER...BUT GIVEN INCREASED SHEAR ACROSS ENTIRE CWA AND
SOME UNCERTAINTY REGARDING WHERE POCKETS OF MODERATE CAPE MAY
RESIDE...WILL ALLOW FOR THE SEVERE THREAT TO INCLUDE ENTIRE CWA IN
HWO AND INCLUDE ENHANCED GUSTY WIND WORDING IN THE GRIDS.
GUSTY/DAMAGING WINDS WILL BE THE PRIMARY SEVERE RISK...HOWEVER
STRONGER CORES THAT EXHIBIT SUFFICIENT VERTICAL GROWTH MAY BE ABLE
TO PRODUCE LARGE HAIL. ANOTHER ELEMENT THAT MUST BE CONSIDERED IS
THE RISK FOR ISOLATED TORNADOES GIVEN THE MAGNITUDE OF THE SHEAR
LATER IN THE DAY/EVENING THAT WILL ENHANCE LOW LEVEL STORM RELATIVE
HELICITY...AS DEPICTED BY THE 21Z SREFS.

REGARDING HIGH TEMPERATURES...POPULATED USING A BLEND OF
MAV/MET/SREFS ALL OF WHICH WERE SIMILAR.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
MINIMAL CHGS MADE TO SHRT TERM PD AS PREV FCST WAS IN GOOD SHAPE.
GENERAL TREND TWD DECRG POPS XCPT PSBLTY OF LGT UPSLP SHRA/TSRA
ALONG ALLEGHENY FRONT. MINIMA WILL BE ELEVATED AGAIN TNGT AS MSTR
RMNS IN PLACE. PREV DISCUSSION FOLLOWS...

PRIMARY SHORTWAVE RESPONSIBLE FOR WIDESPREAD CONVECTION WILL
SWING NORTHEAST THIS EVENING. FLOW WILL BACK SOMEWHAT AS MID LEVEL
WINDS TURN TO THE WEST IN THE WAKE OF THE SHORTWAVE. CONTINUED TO
FOLLOW POP DISTRIBUTION/TRENDS SHOWN BY THE 21Z SREFS.

A HEAVY RAINFALL/SEVERE RISK WILL PERSIST IN THE EARLY EVENING
ACROSS NORTHERN MARYLAND SOUTH THROUGH THE INTERSTATE 95
CORRIDOR...BUT WILL WANE LATER IN THE EVENING AT THE SAME TIME AS
POPS EXHIBIT A DECREASING TREND BEGINNING IN CENTRAL
VIRGINIA...SPREADING NORTHEAST THROUGH THE OVERNIGHT HOURS.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
THURSDAY WILL BE SIMILAR TO YESTERDAY /TUESDAY/ IN TERMS OF POPS W/
MAINLY DRY CONDITIONS OUTSIDE OF A FEW ISOLATED STORMS POPPING UP
UNDER THE VERY WEAK BUT STILL PRESENT INSTABILITY. THE NEAR SFC
ENVIRONMENT WILL STILL BE PLENTY MOIST...SO EVEN W/ A DECENT 600MB
WARM NOSE A FEW BRIEF SHOWERS/TSTMS CAN/T BE RULED OUT. HIGHS AND
CLOUD COVER ALSO FAIRLY SIMILAR TO TUES...W/ TEMPS REACHING THE L90S
UNDER PARTLY SUNNY SKIES.

BUT LIKE YESTERDAY...THURS WILL ALSO BE THE TRANSITION DAY BEFORE
ANOTHER WAVE OF LOW PRESSURE STREAMS NE ACROSS THE ERN SEABOARD
TOWARD NEW ENGLAND. FRI THEN WOULD BE SIMILAR TO TODAY...W/ STEADY
STREAMS OF ISENTROPIC LIFT AND SCATTERED EMBEDDED CONVECTION TRUDGES
FROM THE DEEP SOUTH UP INTO THE NRN REACHES OF NEW ENGLAND.
INCREASED POPS ACROSS THE WRN HALF SINCE THE BEST FORCING ASSOCIATED
W/ THE LL JET MAX WILL SLIDE UP THE SPINE OF THE APLCNS. 00Z RUNS OF
THE GEM/GFS/ECM ALL SHOWING A SUSPECT LWX SPLIT OF MUCH OF THE
HEAVIER PRECIP FOR THE FRIDAY PERIOD...AND EVEN SPEEDING UP THE
PASSAGE OF THE SFC LOW EARLIER IN THE DAY. THIS SOLUTION TAKES THE
COLD FRONT ACROSS THE REGION DURING THE EARLY AFTN HRS...AS OPPOSED
TO PREV RUNS THAT HAD PASSAGE LATER IN THE EVNG. EITHER WAY...THE
NEAR SFC REGIME WILL NOT HAVE BECOME ANY DRIER W/ MODEL PWATS STILL
IN JUST ABOVE 2 INCHES. EVEN WITHOUT BLANKET COVERAGE OF PRECIP AS
THE STRONGEST FORCING GOES BY...THERE WILL BE SFC DEWPOINTS IN THE
70S AND WAVES OF 20-30KT SHEAR IN THE LOWEST FEW THOU FT...CLOSER TO
15-20KT SWLY WINDS AT THE SFC.

LITTLE CHANGE AGAIN BEYOND D3. STILL SEEING AN EXTENDED PERIOD W/
EVERY-OTHER-DAY UPPER WAVES SLIDING AROUND THE BASE OF THE STEADY
UPPER LOW /OVER SRN HUDSON BAY/. THE WEEKEND STILL A BIT
UNCERTAIN...ESPECIALLY W/ CERTAIN MED RANGE MODELS SHOWING A
STATIONARY BOUNDARY JUST SOUTH OF THE REGION SAT...WHICH WOULD KEEP
A LOW CHANCE OF PRECIP OVER THE REGION THRU EARLY NEXT WEEK.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
HAVE INCLUDED MVFR SHRA IN TAFS ATTM DURING THAT PERIOD. THERE
WILL LIKELY BE A BREAK IN CONVECTION WITH POSSIBLE MVFR VSBYS IN
HZ/BR THEREAFTER BEFORE CONVECTION MOVES BACK IN LATER THIS
MORNING/AFTERNOON. HAVE HIGH CONFIDENCE IN OCCURRENCE AND IS
REFLECTED AS PREVAILING SHRA WITH MVFR CONDITIONS IN TAFS. ALSO
TOSSED IN VCTS...WITH ANY TS TIMING/INTENSITY DETAILS TO BE ADDED
IN FUTURE TAF ISSUANCES. AS PRIMARY SHORTWAVE EXITS IN THE
EVENING...CHANCES OF SHRA WILL LOWER ALTHOUGH MVFR BR MAY DEVELOP
LATER AT NIGHT.

MAINLY DRY THURS...MORE WIDESPREAD PRECIP ON FRI. BREEZY CONDITIONS
ON FRI...A BIT WEAKER SFC WINDS ON THURS. LOW CHANCE PRECIP REMAINS
ACROSS THE AREA THRU THE WEEKEND AND INTO EARLY NEXT WEEK.

&&

.MARINE...
LOW LEVEL SOUTHERLY JET INCREASES THIS AFTERNOON...PROVIDING SMALL
CRAFT ADVISORY CALIBER GUSTS AOA 20 KT TO AFFECT ALL MARINE ZONES
LATER IN THE AFTERNOON AND EVENING. IN ADDITION...CONVECTION MAINLY
IN THE AFTERNOON AND EVENING WILL BE CAPABLE OF PRODUCING GUSTY
WINDS WHICH COULD REQUIRE SPECIAL MARINE WARNINGS LATER TODAY.

HAVE REMOVED SMALL CRAFT ADZY FOR THU AS SFC TROF XPCD TO BE IN
VCTY OF WATERS AND WINDS XPCD TO BE LGT DURG MUCH OF DAY. SLY
WINDS MAY BGN TO DVLP BY LATE AFTN BUT CVRG AND DURATION OF ANY 20
KT GUSTS SHUD BE INSUFFICIENT FOR SMALL CRAFT ADZY.

BREEZY CONDITIONS EACH AFTN INTO THE WEEKEND...ESPECIALLY FRI.
HIGH PRESSURE BRIEFLY ON SAT...THEN ANOTHER UPPER LEVEL SYSTEM
ARRIVES INTO THE AREA BY EARLY NEXT WEEK.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EDT THURSDAY FOR ANZ531>534-
     537>543.
     SMALL CRAFT ADVISORY UNTIL 1 AM EDT THURSDAY FOR ANZ530-535-
     536.

&&

UPDATE...KRAMAR
PREV DISCUSSION...BPP/GMS

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1125 AM EDT WED JUL 29 2009

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-
1125 AM EDT WED JUL 29 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

SHOWERS AND THUNDERSTORMS WILL AFFECT THE OUTLOOK AREA TODAY. SOME
OF THE STORMS THIS AFTERNOON AND EVENING MAY BE SEVERE...WITH
DAMAGING WINDS AND ISOLATED LARGE HAIL. ISOLATED TORNADOES WILL
ALSO BE POSSIBLE.

IN ADDITION TO THE SEVERE RISK...THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING VERY HEAVY RAINFALL WHICH COULD CAUSE LOCALIZED FLASH
FLOODING.

A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE TIDAL POTOMAC RIVER
AND MARYLAND CHESAPEAKE BAY THIS AFTERNOON THROUGH LATE TONIGHT.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

SMALL CRAFT ADVISORY CONDITIONS ARE POSSIBLE THURSDAY NIGHT
THROUGH FRIDAY FOR THE TIDAL POTOMAC AND MARYLAND CHESAPEAKE BAY.

SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON.

MDZ003>005-009-010-501-502-VAZ021-025>031-036>042-050-051-
WVZ050>055-501>504-301000-
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-
1125 AM EDT WED JUL 29 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

SHOWERS AND THUNDERSTORMS ARE EXPECTED TODAY MAINLY ALONG AND EAST
OF THE BLUE RIDGE. SOME OF THE STORMS THIS AFTERNOON AND EVENING MAY BE
SEVERE...WITH DAMAGING WINDS AND ISOLATED LARGE HAIL.

IN ADDITION TO THE SEVERE RISK...THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING VERY HEAVY RAINFALL WHICH COULD CAUSE LOCALIZED FLASH
FLOODING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON.