Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 051926 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 326 PM EDT SUN JUL 5 2015 .SYNOPSIS...
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A STATIONARY FRONT WILL REMAIN TO THE SOUTH THROUGH TONIGHT...BEFORE LIFTING NORTH AS A WARM FRONT MONDAY. A WEAK COLD FRONT WILL APPROACH THE REGION WEDNESDAY...THEN LINGER OVER OUR AREA THROUGH THE EXTENDED.
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&& .NEAR TERM /THROUGH MONDAY NIGHT/...
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CONVECTION BEGINNING TO DEVELOP LATE THIS AFTN...MAINLY WEST OF THE BLUE RIDGE. OVERALL PICTURE...STATIONARY FRONT HOVERING ALONG THE VA/NC BORDER WITH UPPER LVL TROUGH WITH ASSOCIATED SHORTWAVE NOTED OVER THE OH RIVER VALLEY...PER LATEST WATER VAPOR IMAGERY. EXPECTING THE CONVECTION TO INCREASE IN COVERAGE THRU THE REMAINDER OF THE AFTN INTO TONIGHT AS THESE FACTORS COME INTO PLAY. FOR THIS EVENING AND OVERNIGHT...FLASH FLOOD WATCH HAS BEEN ISSUED FOR HIGHLAND AND PENDLETON COUNTIES. SHORTWAVE PIVOTING MAINLY WEST OF THE BLUE RIDGE WILL TRIGGER NUM SHOWERS AND EMBEDDED TSTMS LASTING THRU NEAR DAYBREAK MON MORNING. WATER VAPOR IMAGERY SHOWS STRONG SURGE OF MOISTURE FROM THE GOM REACHING THE WESTERN AREAS...INCRSG PWATS TO AROUND 1.75 INCHES TONIGHT. THIS COMBINED WITH A GENERALLY SLOW FLOW WILL RESULT IN HEAVY RAINFALL...WHICH COULD LEAD TO FLASH FLOODING. HAVE ISSUED THE WATCH FOR THE AREAS THAT ARE SHOWING THE BEST CHC FOR CONVECTION AND THE LOWEST FFG GUIDANCE...WITH 1 HR SHOWING AROUND 1 INCH. OTHER AREAS WEST OF THE BLUE RIDGE COULD SEE HEAVY DOWNPOURS TONIGHT...BUT WITH THE HIGHER FFG FELT THE THREAT WAS MORE MINIMAL. THE STATIONARY FRONT WILL EVENTUALLY BEGIN TO LIFT NORTH AS A WARM FRONT TONIGHT...EVENTUALLY PUSHING NORTH OF THE AREA BY MONDAY NIGHT. THINKING THE FRONT WILL PROVIDE THE NEEDED FORCING TO TRIGGER SHOWERS EAST OF THE BLUE RIDGE AS THE SHORTWAVE ENERGY LOOKS TO STAY MORE TO THE WEST. AS SUCH...HAVE HIGHER POPS WEST FIRST HALF OF THE NIGHT...THEN PUSHING EAST SECOND HALF OF THE NIGHT. SOME QUESTION AS TO HOW LONG THE PCPN LINGERS IN THE MORNING...THOUGH GENERAL IDEA WOULD BE SOME CLEARING MON MORNING BEFORE THE NEXT ROUND OF CONVECTION THEN MON AFTN AS THE WARM FRONT LIFTS THROUGH AND THE NEXT SHORTWAVE MOVES THROUGH. THIS SHORTWAVE LOOKS TO BE FURTHER EAST...SO THE THREAT OF OF TSTMS ENCOMPASSES THE ENTIRE AREA MON AFTN/EVENING. SVR THREAT LOOKS TO BE MORE MARGINAL AS INSTABILITY IS CURRENTLY LIMITED. HOWEVER...IF WE CAN SCATTER OUT MORE IN THE MORNING...COULD SEE BETTER INSTABILITY. SHEAR IS STRONGER ON MONDAY...THOUGH STILL NOT COMPLETELY SELLING ON SVR. BACKING WINDS WITH THE WARM FRONT COULD HINT AT PSBL TOR THREAT...BUT STILL ON THE LOW END. WILL HIGHLIGHT THAT HEAVY RAIN WILL BE A THREAT AGAIN MON AFTN AS PWATS STAY WELL ABV NORMAL...ESP OVER EASTERN AREAS. PCPN WILL SLOWLY TAPER OFF MON NIGHT AS THE FRONT CLEARS TO THE NORTH.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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MID/UPPER LEVEL LOW STARTS PULLING AWAY FROM OUR AREA TUESDAY MORNING...AS IT IS SHEARED APART...AND IS INGESTED INTO MAIN BELT OF WESTERLIES ASSOCIATED WITH THE NORTHERN STREAM. MOST OF TUE APPEARS TO BE RELATIVELY DRY UNDER SUBSIDENCE FROM DEPARTING LOW AND LITTLE IN THE WAY OF LIFTING MECHANISMS IN THE AREA. ALTHOUGH...CANNOT ENTIRELY RULE OUT AN ISOLATED AFTN TSTM WITH SFC HEATING COMBINED WITH MESOSCALE FEATURES (SUBTLE BOUNDARIES...TERRAIN)...THOUGH ATTM CHCS APPEAR VERY LOW. GUIDANCE HAS BEEN TRENDING HIGHER WITH TEMPS...LIKELY DUE TO MORE INSOLATION...SO NUDGED THEM UP A BIT WITH TEMPS IN THE U80S ACROSS THE REGION. LIGHT SWLY WINDS USHER IN SOME DRIER AIR...WHICH KEEP HEAT INDICES IN L90S. WEAK COLD FRONT APPROACHES THE REGION WED. INCREASED POPS SOMEWHAT IN THE AFTN...AS QPF SIGNAL IS BECOMING MORE CONSISTENT. DEEP LAYER FLOW REMAINS RATHER WEAK THROUGH THE PERIOD AND INSTABILITY IS ALSO RATHER LIMITED...SO EXPECTING MOST ACTIVITY TO BE UNORGANIZED. TEMPS INCREASE SLIGHTLY UNDER CONTINUED AIRMASS MODIFICATION...BUT SHOULD ONLY BE A FEW DEGREES ABOVE CLIMO NORMS.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/...
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COLD FRONT MOVES OVER THE CWA WED NIGHT AND LINGERS THROUGH THE WEEKEND. INSTABILITY FROM THIS SYSTEM WILL ALLOW FOR THE RISK OF ISOLATED/SCATTERED SHOWERS AND/OR TSTMS EACH DAY. TEMPS WILL BE NEAR NORMAL FOR THIS TIME OF THE YEAR.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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GENERALLY VFR CONDITIONS THRU THIS EVENING. LOW CONFIDENCE OF PCPN IMPACTING TERMINALS OTHER THAN KCHO THRU THE EVENING. INCRSG CONFIDENCE FOR THE SECOND HALF OF THE NIGHT FOR ALL SITES WITH SHOWERS...PSBL THUNDER...AND SUB-VFR CONDITIONS. HEAVY DOWNPOURS WILL PRODUCE IFR CIGS AND VIS. VFR CONDITIONS RETURN MON MORNING AS THE PCPN TAPERS OFF. ANOTHER ROUND OF SHOWERS AND TSTMS LIKELY MON AFTN WHICH ONCE AGAIN WILL RESULT IN SUB-VFR CONDITIONS. WINDS GENERALLY 10 KTS OR LESS FROM THE SE THRU MON. ANY TSTM COULD PRODUCE SPORADIC GUSTS UP TO 40 KTS. EXPECT VFR CONDS TUE...AS MID/UPPER LOW DEPARTS OUR AREA AND WE ARE IN REGION OF SUBSIDENCE. ATTM VERY LOW CHC FOR AFTN TSTM TUE WITH LOCALIZED SUB-VFR CONDS IF THEY OCCUR. BETTER CHCS FOR SHWRS/TSTMS...AND LOCALIZED SUB-VFR CONDS ON WED AS COLD FRONT APPROACHES THE REGION. VFR CONDITIONS EXPECTED FOR WED NIGHT AND THURS. SUB-VFR CONDITIONS PSBL DUE TO SHOWERS AND/OR TSTMS.
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&& .MARINE...
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SUB-SCA CONDITIONS ON ALL WATERS THRU MON MORNING. HAVE ISSUED A SCA FOR THE LOWER TIDAL POTOMAC AND CHESAPEAKE BAY MON AFTN AND EVENING FOR INCRG SLY FLOW RESULTING IN GUSTS UP TO 20 KTS. SUB- SCA CONDITIONS RETURN FOR ALL WATERS MON NIGHT. WINDS EXPECTED TO SUBSIDE TUE MORNING AS PRESSURE GRADIENT RELAXES AND REGION IS UNDER SUBSIDENCE FROM DEPARTING LOW. WINDS EXPECTED TO REMAIN BELOW SCA CRITERIA THROUGH WED...THOUGH MARINERS SHOULD WATCH OUT FOR TSTM CHCS WED AFTN. SUB-SCA CONDITIONS EXPECTED FOR WED NIGHT AND THURS. PSBL SHOWERS AND TSTMS ACROSS THE WATERS DURING THIS PERIOD.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ503-504. WV...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR WVZ505-506. MARINE...SMALL CRAFT ADVISORY FROM 2 PM MONDAY TO 2 AM EDT TUESDAY FOR ANZ534-537-543.
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&& $$ SYNOPSIS...SEARS/MSE NEAR TERM...SEARS SHORT TERM...MSE LONG TERM...IMR AVIATION...SEARS/IMR/MSE MARINE...SEARS/IMR/MSE

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