Flash Flood Warning 58, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1000 PM EDT TUE JUN 21 2011

.SYNOPSIS...
AN UPPER RIDGE BUILDS ACROSS THE MID-ATLANTIC REGION THROUGH
THURSDAY. A COLD FRONT WILL APPROACH THE MID-ATLANTIC THURSDAY
NIGHT AND FRIDAY...BUT MAY NOT PUSH SOUTH OF THE AREA UNTIL LATE
SATURDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
CURRENT ANALYSIS THIS EVENING SHOWS AN UPPER-LEVEL RIDGE OVERHEAD
WHILE AN UPPER-LEVEL LOW CONTINUES TO SPIN OVER THE CENTRAL CONUS.
HIGH PRESSURE REMAINS OVER THE ATLANTIC AND A SOUTHERLY FLOW
AROUND THE HIGH HAS BROUGHT A RETURN OF WARM AND HUMID CONDITIONS.

LATEST MESOANALYSIS ALONG WITH 00Z KIAD RAOB SHOWS MODERATE
INSTABILITY THIS EVENING. SHOWERS AND THUNDERSTORMS HAVE BECOME
MORE NUMEROUS ACROSS THE SHENANDOAH VALLEY AS THEY FEED OFF THE
OUTLOW BOUNDARIES FROM PREVIOUS CONVECTION. HAVE UPDATED POPS
ACROSS THIS AREA. WEAK SHEAR PROFILES SUGGESTS THAT THE SEVERE
THREAT WILL BE LIMITED...BUT AN ISOLATED SEVERE STORM CANNOT BE
RULED OUT LATE THIS EVENING.

THE RIDGE AXIS WILL GRADUALLY SHIFT EAST OVERNIGHT. AN AREA OF
LIFT ASSOCIATED WITH THE 700-500MB WARM FRONT IS LOCATED JUST
WEST OF THE RIDGE AXIS. THE WARM FRONT IS EXPECTED TO PASS THROUGH
THE REGION OVERNIGHT. SINCE THIS FEATURE WILL PASSING THROUGH
OVERNIGHT INSTABILITY WILL NOT BE AS HIGH AS THIS AFTERNOON OR
EVENING. THIS WILL LIMIT ANY THREAT FOR SEVERE T-STORMS BUT
SCATTERED SHOWERS AND T-STORMS WILL CONTAIN LOCALLY HEAVY RAIN.
HAVE KEPT THE HIGHEST POPS ACROSS THE NORTHERN AND WESTERN CWA
WHERE THE LIFT WILL BE MORE PROMINENT.

AS WMFNT ALOFT CONTS TO PUSH NEWD...CWFA WL BE MORE W/IN THE WARM
SECTOR TMRW. RDG AXIS WL BE A BIT FURTHER EWD TOO...SO TSTMS FM
UPR OHVLY WL HV A BETTER CHC AT SURVIVING. THE PERFERRED LOCATION
FOR TSTMS REMAINS ACRS NRN MD DUE TO PROXIMITY TO TRIGGERING
BNDRYS. HWVR...AMS WL BE EQUALLY HUMID AND UNSHEARED
THRUT...SUPPORTIVE OF A LEE SFC TROF. GIVEN THAT SETUP...STRONG
SLOW MVG TSTMS CUD DVLP ANYWHERE. AS ANTICIPATED FOR THOSE
DEWPTS...PWATS RATHER HIGH /CLOSE TO 1.75IN/. WL KEEP THE THEME OF
HIEST POPS IN THE AFTN...LKLY N AND CHC S. HVY RAINS AND LCL
DOWNBURST WNDS PRIMARY THREATS. THERE SEEMS TO BE A BIT TOO MUCH
DEBRIS ARND TO SUPPORT MAV MAXT /LWR-MID 90S A-PLENTY/...SO CHOSE
A RTE SLIGHTLY WARMER THAN THE MET.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
MID-ATLC WILL RESIDE IN SWLY L/MLVL FLOW THRU FRI WITH UPR TROF OVR
GREAT LKS AND SUBTROPICAL RDGG ACRS SERN CONUS. SCATTERED CNVCTN WED
NGT SHUD WANE DIURNALLY AS INSTABILITY DECREASES...BUT WILL LIKELY
INCREASE IN CVRG AND INTENSITY BY THU AFTN. IN ADDITION TO LEE TROF
THAT WILL RMN IN PLACE OVR THE AREA...CONVERGENCE IN ASSOCIATION WITH
CDFNT MOVG ACRS APLCNS SHUD AID IN CNVCTN THU AFTN. HIGHLY UNSTABLE
ATMOSPHERE AND DECENT 0-6KM WIND SHEAR SHUD SUPPORT STRONG
UPDRAFTS/ORGANIZED CLUSTERS OF TSTMS...WITH RISK OF SVR WX ACRS CWA
DURG AFTN AND EVE. ACTIVITY SHUD AGAIN DIMINISH A BIT OVNGT BUT
REDEVELOP BY FRI AFTN.  TEMPS WILL BE NEAR/SLIGHTLY ABV NRML...WITH
MAXIMA AVGG IN U80S AND MINIMA FROM M60S TO L70S.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
OVERALL WX PATTERN SLOW TO CHANGE THIS WKEND...AND TEMPS SHUD REMAIN
WITHIN A FEW DEGREES OF AVERAGE FOR EARLY SUMMER. GREAT LAKES UPR
TROF XPCD TO LIFT INTO NEW ENGLAND...CREATING MORE WLY FLOW ACRS
MID-ALTC. MODELS LESS AMBITIOUS WITH SWD PROGRESS OF DRIER AREA INTO
THE RGN...SO WILL CONT POPS INTO SAT. ANY WKEND BREAK IN TSTM CHCS
LIKELY TO BE SHORT-LIVED...AS ANOTHER ULVL TROF POISED TO SET UP W
OF CWA BY EARLY NEXT WK.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
SCATTERED SHOWERS AND T-STORMS ARE EXPECTED THIS EVENING. THE BEST
CHANCE FOR CONVECTION WILL BE ACROSS KIAD AND KDCA. SCATTERED
SHOWERS AND T-STORMS MAY AFFECT THE TERMINALS OVERNIGHT INTO EARLY
WEDNESDAY. THE BEST CHANCE WILL BE ACROSS THE NORTHERN TERMINALS.
PATCHY BR WILL REDUCE VSBYS TO MVFR LEVELS LATE TONIGHT.

AN ACTIVE AND UNSTABLE PATTERN WILL PROMOTE SHOWERS AND
THUNDERSTORMS WED.

CHC OF SHWRS/TSTMS THRU SAT AS UNSTABLE EARLY SUMMER ATMOSPHERE
REMAINS IN PLACE ACRS MID-ATLC. ACTIVITY SHUD PEAK DURG AFTN/EVE.

&&

.MARINE...
A SMALL CRAFT ADVISORY IS IN EFFECT UNTIL MIDNIGHT FOR THE LOWER
TIDAL POTOMAC RIVER AND MARYLAND CHESAPEAKE BAY SOUTH OF NORTH
BEACH. SOUTHERLY WINDS WILL CHANNEL UP THESE LOCATIONS AND WIND
GUSTS UP TO 20 KNOTS ARE EXPECTED DURING THIS TIME. THE GRADIENT
WILL DIMINISH OVERNIGHT. SCATTERED SHOWERS AND T-STORMS ARE
POSSIBLE TONIGHT AS AN UPPER-LEVEL RIDGE MOVES OFFSHORE.

THERE IS A BETTER CHANCE FOR SHOWERS AND T-STORMS WEDNESDAY
AFTERNOON DUE TO HIGHER AMOUNTS OF INSTABILITY. T-STORMS MAY
CONTAIN GUSTY WINDS AND HAIL.

SSW FLOW IN ADVANCE OF SLOWLY APPROACH CDFNT WILL INCR TO NEAR SCA
THRESHOLDS WED NGT AND THU...ESPECIALLY IN CHANNELING OVR
CHESAPEAKE BAY. NOT CONFIDENT ENUF IN 20 KT GUSTS TO ISSUE HEADLINES
ATTM. DECENT SSW WINDS EXPECTED INTO SAT BEFORE FLOW BCMS MORE WLY.
SCATTERED THUNDERSTORMS PSBL...ESPECIALLY DURG AFTN/EVE.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES REMAIN AROUND ONE HALF FOOT TO ONE FOOT ABOVE
NORMAL THIS EVENING. A SOUTHERLY FLOW HAS INCREASED...BUT WATER
LEVELS WILL LIKELY REMAIN BELOW MINOR THRESHOLDS FOR COASTAL
FLOODING SINCE THE HIGH TIDE THIS EVENING INTO OVERNIGHT WILL BE
THE LOWER OF THE TWO HIGH TIDES.

SOUTHERLY FLOW WILL CONTINUE WEDNESDAY SO POSITIVE TIDAL ANOMALIES
ARE EXPECTED TO CONTINUE. WATER LVLS WL STILL NEED TO BE
MONITORED FOR POTENTIAL MINOR OVERFLOWS IN SENSITIVE LOCATIONS AT
THE TIME OF HIGH TIDE WEDNESDAY MORNING THROUGH MIDDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ533-534-
     537-541>543.

&&

LASORSA/HTS/SBK

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
953 PM EDT TUE JUN 21 2011

VAZ026-220230-
ROCKINGHAM VA-
953 PM EDT TUE JUN 21 2011

...STRONG THUNDERSTORM TO AFFECT ROCKINGHAM COUNTY...

AT 953 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 2 MILES
SOUTH OF PENN LAIRD...MOVING NORTHEAST AT 20 MPH.

LOCATIONS IMPACTED INCLUDE MASSANUTTEN.

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.

SMALL HAIL CAN BE EXPECTED WITH THIS STORM.

WIND GUSTS OF 40 TO 50 MPH CAN BE EXPECTED WITH THIS STORM.

&&

LAT...LON 3852 7874 3841 7853 3829 7880 3835 7890
TIME...MOT...LOC 0153Z 227DEG 18KT 3836 7880

KRAMAR