AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 354 AM EDT FRI JUL 8 2011 .SYNOPSIS... A STATIONARY FRONT WILL REMAIN NEAR THE MASON DIXON LINE EARLY TODAY...BUT BEGIN TO PUSH SOUTHWARD OVERNIGHT. HIGH PRESSURE WILL BUILD IN FROM THE NORTH EARLY SATURDAY AND REMAIN IN PLACE THROUGH THE WEEKEND. A SECOND FRONT WILL PUSH SOUTH ACROSS THE MID ATLANTIC LATE MONDAY INTO TUESDAY...WITH HIGH PRESSURE RETURNING FOR THE SECOND HALF OF THE WEEK. && .NEAR TERM /UNTIL NOON TODAY/... AN ACTIVE COUPLE OF HOURS TO END THU AND START OFF FRI...ESPECIALLY FOR THE NRN HALF OF THE CWA. SHOWER AND TSTM ACTIVITY W/ HIGH RAINFALL RATES /A PRECURSOR TO WHAT IS EXPECTED LATER TODAY/ DEVELOP QUICKLY ALONG THE STALLED BOUNDARY DRAPED NEAR THE MASON-DIXON LINE. THE BOUNDARY WILL AGAIN BE THE FOCUS FOR SOME SCATTERED ACTIVITY BUT IT WILL CERTAINLY ONLY BE ONE PLAYER IN THE SCENARIO UNFOLDING FOR LATER THIS AFTN/EVE. A BROADER SCOPE SHOWS A LARGE BATCH OF STRATIFORM PRECIP STREWN ACROSS THE OHIO RVR VLY FROM THE MS/OHIO RVR CONFLUENCE TO THE CINCINNATI AREA. WHILE MUCH OF THE AREA IN BETWEEN US AND THE OHIO VLY IS INACTIVE CURRENTLY...THESE AREAS WILL BEGIN TO FILL-IN W/ SCATTERED SHOWERS AND SOME ISOLATED CONVECTION HEADING INTO THE MID MORNING AND EVEN THE PREDAWN HRS. MUCH OF THE ERN SEABOARD BEING FED A SOLID FETCH OF GULF MOISTURE...DRIVEN BY A POTENT UPPER LEVEL LOW OFF THE LOUISIANA COAST - IN CONCERT W/ A DEVELOPING TROPICAL FEATURE OVER FLORIDA. ATMOSPHERIC PROFILES ACROSS THE DEEP SOUTH AND UP THE EAST COAST ARE FAIRLY MOIST W/ ONLY MINOR SUBSIDENCE REGIONS INTERSPERSED. ALL OF THIS ADDING TO THE SET-UP W/ SFC DEWPOINTS RISING ABOVE 70 /AND STAYING THERE/ WELL INTO SATURDAY. NOT MUCH ORGANIZED LIFT IS NECESSARY FOR DEVELOPMENT OF SHOWERS AND WEAK CONVECTION...JUST A PASSING BOUNDARY OR A STATIONARY ONE. OVER THE NEXT SEVERAL HRS...SKIES WILL CONTINUE TO CLEAR OUT AHEAD OF THE INCOMING SHORTWAVE FROM THE OHIO VLY. SOME MID LEVEL CLOUD DEBRIS WILL SLIDE OVER THE AREA AROUND SUNRISE...A WITHIN A COUPLE HRS OF SUNRISE...ISOLATED SHOWERS AND STORMS ARE EXPECTED TO BEGIN POPPING UP ACROSS THE ERN SEABOARD AND APLCN CHAIN. WEAK BUT SUFFICIENT 15-20KT STEERING FLOW WILL PUSH THIS ACTIVITY ENE CARRYING LOCALLY HEAVY RAIN BUT NOT WIDESPREAD. AS THE SHORTWAVE NEARS THE WRN ZONES...MORE WIDESPREAD ACTIVITY WILL DEVELOP AND BEGIN TO PUSH INTO THE AREA. && .SHORT TERM /NOON TODAY THROUGH 6 AM SATURDAY/... INSTABILITY HAS NOT AND WON/T DROP OFF MUCH DURING THE OVERNIGHT HRS...BEFORE BUILDING BACK UP AGAIN AFTER SUNRISE. IN TERMS OF HIGH RAINFALL RATES...SUBSTANTIAL INSTABILITY NOT NECESSARY - VALUES IN THE 1000-2000 RANGE /WHICH IS FORECASTED FOR THE MID ATLC REGION/ IS SUFFICIENT FOR INITIATION AND MAINTENANCE OF WARM CLOUD PROCESSES AND EFFICIENT HEAVY RAIN-MAKERS. PWATS WILL BE OVER 2 INCHES LATER THIS AFTN/EVE AS THE HEIGHT OF ACTIVITY IS EXPECTED ACROSS THE AREA. AS SEEN W/ YESTERDAYS CONVECTION...WET MICROBURSTS WILL BE PREVALENT W/ THE STRONGEST UPDRAFTS AND EVEN WEAKER STORMS WILL CREATE GUSTY WINDS IN LOCALIZED AREAS. HAIL WILL ALSO BE POSSIBLE W/ MAXIMUM INSTABILITY DURING THE LATE AFTN/EVE HRS...THEN TRANSFORM INTO MORE OF A DAMAGING WIND THREAT OVERNIGHT. THE NAM CONTINUES TO BE /BY FAR/ THE MOST AGGRESSIVE IN TERMS OF QPF AMOUNTS AND POSSIBLY EVEN RESIDENCE TIME OF THE HEAVIEST ACTIVITY IS IT MOVES ACROSS THE CWA. FLASH FLOOD WATCH IN EFFECT FOR MUCH OF THE DAY AND INTO THIS TIME OVERNIGHT FOR THE AREA OUTSIDE OF THE POTOMAC HIGHLANDS/NRNMOST SHENANDOAH VLY. && .LONG TERM /SATURDAY THROUGH THURSDAY/... LINGERING SHOWERS ASSOCIATED WITH A SLOW MOVING FRONTAL BOUNDARY POSSIBLE ACROSS THE SOUTHERN PORTION OF THE CWFA EARLY SATURDAY MORNING. PRECIP SHOULD TAPER OFF BY THE AFTERNOON AS THE FRONT CONTINUES SOUTHWARD AND HIGH PRESSURE BUILDS IN FROM THE NORTH. HIGH PRESSURE WILL REMAIN THE DOMINANT WEATHER FEATURE THROUGH THE WEEKEND...BUT WILL MOVE OFFSHORE ON MONDAY. A SECOND FRONT IS EXPECTED TO IMPACT THE CWFA BY LATE MONDAY/EARLY TUESDAY BRINGING ANOTHER CHANCE OF SHOWERS/TSRA. HIGH PRESSURE BUILDS IN FROM THE NORTH FOR THE LATTER HALF OF THE WEEK. ONLY MINOR CHANGES TO DAYS 3 INTO 4. NO CHANGES PAST DAY 5. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... SCATTERED BATCHES OF 4-6KFT LEFTOVER CIGS FROM EARLIER CONVECTION AND BECAUSE THE LOW LEVELS ARE VERY MOIST. NOT EXPECTING TOO MUCH OF FOG THREAT INTO THE PREDAWN HRS...SINCE ENOUGH CLOUD COVER WILL BE SLIDING ACROSS THE AREA. PLENTY OF LOW LEVEL MOISTURE EXISTS THOUGH...WHICH WILL CREATE A SCENARIO FOR LOCALIZED HEAVY RAIN W/ WIDESPREAD SHOWER/TSTM ACTIVITY LATER THIS AFTN AND UNTIL ABOUT THIS TIME /4-8Z/ SAT MORNING. THE THREAT FOR MID ATLC AIRPORTS REPRESENTED BY CB GROUPS AND SINCE ACTIVITY WILL BE MAINLY RAIN /HEAVY AT TIMES/ WITH LESSER CHANCES FOR TSTMS TO MOVE OVER INDIVIDUAL AIRPORTS. CONDITIONS WILL IMPROVE GRADUALLY DURING THE PREDAWN HRS SAT...AS A FRONT SLIDES DOWN FROM THE NW AND SWEEPS THIS ACTIVITY OFF THE COAST. SUB VFR CONDITIONS POSSIBLE AT KCHO EARLY SATURDAY MORNING. HOWEVER...ANY LINGERING SHOWERS FROM THE SLOW MOVING FRONT SHOULD BEGIN TO PUSH SOUTHWARD BY THE AFTERNOON. NO CIG/VSBY RESTRICTIONS EXPECTED FOR THE REMAINDER OF THE WEEKEND. A SECOND FRONT COULD BRING SUB VFR CONDITIONS BACK TO THE REGION LATE MONDAY INTO TUESDAY. && .MARINE... WEAK SLY CHANNELING OVER THE LOWER BAY OVERNIGHT BUT ONLY NEAR 10KT. MORE RANDOM WIND PATTERNS ACROSS THE REST OF THE WATERS...W/ A STATIONARY FRONTAL BOUNDARY DRAPED OVER THE AREA. LITTLE CHANGE FOR THE REST OF THE DAY...OTHER THAN A MINOR STRENGTHENING OF THE SLY COMPONENT OVER MORE OF THE WATERS THRU MID AFTN. SHOWERS AND SOME TSTM ACTIVITY WILL DEVELOP AS THE DAY PROGRESSES AND AFFECT THE WATERS WELL INTO THE OVERNIGHT HRS. SMW-STRENGTH WINDS WILL BE POSSIBLE UNDER THE STRONGER TSTMS THAT NEAR THE BAY/TP. DURING THE OVERNIGHT PERIOD...THE STATIONARY BOUNDARY WILL GRADUALLY DRIFT SEWD AND OFF THE COAST INTO THE PREDAWN HRS SAT. HIGH PRESSURE BUILDS IN BEHIND A FRONT ON SATURDAY. HIGH PRESSURE REMAINS OVERHEAD THROUGH EARLY MONDAY. AS SECOND FRONT MAY IMPACT THE WATERS BY LATE MONDAY/EARLY TUESDAY. NO HEADLINES ANTICIPATED AT THIS TIME. && .HYDROLOGY... NO CHANGES TO THE FLASH FLOOD WATCH AT THIS TIME...AND POTENTIAL FOR HEAVY RAINS CONTINUES AS TROPICAL MOISTURE FROM THE GULF OF MEXICO INTERACTS WITH A SLOW MOVING FRONTAL BOUNDARY. MODELS PROG THE PWATS THIS EVENING AROUND 2.25 INCHES...WHICH IS WELL ABOVE 2SD ABOVE NORMAL. IN ADDITION...QUASI-STATIONARY/SLOW MOVING FRONT WILL PROVIDE A FOCUS FOR TRAINING STORMS. BOUNDARY LAYER FLOW ALSO REMAINS LIGHT AOB 15KT. ATMOS REMAINS UNSTABLE WITH DEWPOINTS IN THE LOWER 70S. ALREADY HAVE SEEN SOME STORMS PRODUCE FLASH FLOODING CONDITIONS ACROSS BALTIMORE COUNTY...WITH RADAR ESTIMATES OF AROUND 4-4.5 INCHES ACROSS CENTRAL BALTIMORE COUNTY WHERE STORMS TRAINED FOR SEVERAL HOURS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...FLASH FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR DCZ001. MD...FLASH FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR MDZ004>007-009>011-013-014-016>018. VA...FLASH FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR VAZ025>027-029>031-036>040-042-050>057-501>504. WV...FLASH FLOOD WATCH FROM NOON EDT TODAY THROUGH LATE TONIGHT FOR WVZ505-506. MARINE...NONE. && $$ SYNOPSIS...LISTEMAA