Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 261908 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 308 PM EDT SAT JUL 26 2014 .SYNOPSIS... HIGH PRESSURE IS MOVING OFFSHORE. LOW PRESSURE IS EXPECTED TO TRACK ACROSS PENNSYLVANIA SUNDAY NIGHT WITH AN ASSOCIATED COLD FRONT MOVING INTO THE MID ATLANTIC. A REINFORCING FRONT WILL CROSS THE REGION MONDAY. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT BRINGING COOLER AND DRIER CONDITIONS DURING MIDWEEK. && .NEAR TERM /THROUGH SUNDAY/... HIGH PRESSURE HAS MOVED FURTHER OFF THE COAST THIS AFTERNOON WHILE A SFC TROUGH HAS DEVELOPED ACROSS THE MID-ATLANTIC. A TIGHT DEWPT GRADIENT PERSISTS NEAR THE BLUE RIDGE. A SHORTWAVE TROUGH HAS MOVED OFF THE EAST COAST EARLY THIS AFTERNOON. A LINE OF SHOWERS AND THUNDERSTORMS FORMED ON AN OUTFLOW BOUNDARY FROM MORNING SHOWERS TODAY. THESE SHOWERS HAVE INTENSIFIED AS THEY ENTERED AN AREA OF HIGHER INSTABILITY AND MOVED ACROSS WARM WATERS. SUBSIDENCE BEHIND THE DEPARTING SHORTWAVE HAS LEFT THE REMAINING LOOKOUT AREA MOSTLY SUNNY WITH TEMPS REACHING THE MID TO UPPER 80S. WARM AIR ADVECTION WILL INCREASE THIS EVENING AS A WARM FRONT APPROACHES THE REGION. THIS WILL BE THE BEGINNING OF DETERIORATING CONDITIONS ACROSS THE MID-ATLANTIC AS WINDS ALOFT INCREASE. SCT SHOWERS AND THUNDERSTORMS ARE POSSIBLE ACROSS THE HIGHLANDS LATE TONIGHT AS WAA MOVES INTO THE REGION. REMNANTS OF SEVERE THUNDERSTORMS WILL CONGEAL INTO A MCS ACROSS THE OHIO VALLEY LATE TONIGHT. THIS ACTIVITY WILL BE AHEAD OF A COLD FRONT AND ASSOCIATED SFC LOW AND IS HARD TO PINPOINT THE EVOLUTION. THERE ARE DIFFERENT SOLUTIONS FOR THE TRACK AND SPEED OF THIS MCS AT THIS TIME BUT ALL SOLUTIONS SHOW A FEATURE TRACKING ACROSS THE OHIO VALLEY AND REACHING THE MID ATLANTIC LATE TONIGHT AND INTO SUNDAY MORNING. HEAVY RAIN AND THUNDERSTORMS ARE EXPECTED TO MOVE INTO THE POTOMAC HIGHLANDS EARLY SUNDAY MORNING AND TRACK EASTWARD. INSTABILITY WILL LOW SUNDAY MORNING BUT SHEAR WILL BE INCREASING AND AT THIS TIME THUNDERSTORMS ARE EXPECTED TO BE SUB-SEVERE. THIS MCS/SHORTWAVE TROUGH SHOULD MOVE ACROSS THE REGION BY SUNDAY AFTERNOON AND SUBSIDENCE BEHIND IT WILL LEAD TO SOME BREAKS IN THE CLOUDS. DESTABILIZATION ON SUNDAY WILL DEPEND ON THE TRACK AND SPEED OF THIS MCS. OVERALL...INSTABILITY IS PROJECTED TO INCREASE TO AROUND 2K J/KG SUNDAY AFTERNOON. AT THIS TIME...SHEAR PROFILES WILL HAVE ALSO INCREASED WITH 40-50KTS OF 0-6 KM SHEAR ACROSS THE REGION WITH A MAJORITY OF THAT BETWEEN 0-1KM. THE COLD FRONT IS EXPECTED TO PRODUCE DISCRETE STRONG TO SEVERE CELLS ACROSS THE OHIO VALLEY SUNDAY AFTERNOON. THIS ACTIVITY WILL TRACK EASTWARD AND REACH THE POTOMAC HIGHLANDS SUN LATE AFTERNOON REACHING THE INTERSTATE 95 CORRIDOR AFTER 8 PM. AHEAD OF THE FRONT THUNDERSTORMS ARE EXPECTED ALONG OUTFLOW/DIFFERENTIAL HEATING BOUNDARIES FROM DEPARTING MCS. THE ATM WILL BE CONDUCIVE FOR SEVERE THUNDERSTORMS CAPABLE OF SUPERCELLS. CURVED HODOGRAPHS WITH 50KTS OF SHEAR WILL LIKELY CAUSE DMG WINDS...LARGE HAIL AND TORNADOES. SUPERCELLS WILL BE CAPABLE OF SPAWNING A COUPLE TORNADOES. THESE SIGNALS ARE STRONGER THAN THE MID-ATLANTIC USUALLY WITNESSES. PLEASE USE CAUTION SUNDAY AND SUNDAY NIGHT AND MAKE SURE YOU ARE NEAR AN OUTLET TO RECEIVE UP TO DATE WEATHER INFORMATION. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/... THUNDERSTORMS WILL CONTINUE INTO SUNDAY NIGHT AND EARLY MONDAY AS THE COLD FRONT CROSSES THE MID-ATLANTIC. SHOWERS SHOULD BE OUT OF THE REGION BY SUNRISE ON MONDAY AS THE LOW MOVES INTO NEW ENGLAND. THE UPPER LEVEL TROUGH WILL BE MOVING OVER THE PA MONDAY AND COLD AIR ADVECTION WILL LIKELY PRODUCE A CU FIELD ACROSS THE AREA. SHOWERS AND ISO THUNDERSTORMS WITH GUSTY WINDS DUE TO AN INVERTED V SIGNATURE WILL BE POSSIBLE. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A LARGE AREA OF HIGH PRESSURE WILL BUILD SOUTH INTO THE AREA FROM CANADA...RESULTING TO MUCH DRIER AND COOLER CONDITIONS FOR THE MIDDLE PART OF THE WEEK. SUBSIDENCE WITH RIDGING ALOFT AND DRY AIR IN THE LOW LEVELS SHOULD PRECLUDE ANY CONVECTION DURING THIS TIME. TEMPERATURES WILL ALSO BE SEVERAL DEGREES BELOW NORMAL. THE RIDGE OF HIGH PRESSURE WILL BEGIN TO PUSH OFFSHORE LATER IN THE WEEK AS ANOTHER SLOW MOVING UPPER LEVEL TROUGH APPROACHES FROM THE WEST...RESULTING IN AN INCREASE IN SHOWER AND THUNDERSTORM CHANCES BY NEXT WEEKEND. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... VFR CONDITIONS EXPECTED TODAY AND TONIGHT. SHOWERS AND THUNDERSTORMS WILL APPROACH MRB LATE TONIGHT AND MOVE EASTWARD. VSBYS WILL LIKELY DROP TO MVFR/IFR IN HEAVY SHOWERS AND THUNDERSTORMS. ANOTHER ROUND OF THUNDERSTORMS WILL MOVE INTO THE REGION SUNDAY AFTERNOON AND EVENING. THESE THUNDERSTORMS ARE EXPECTED TO BE STRONG TO SEVERE WITH DMG WINDS LARGE HAIL AND TORNADOES. HEAVY RAIN IS ALSO POSSIBLE. THIS WILL CONTINUE INTO SUNDAY NIGHT. VSBYS/CIGS WILL BE REDUCED IN THUNDERSTORMS DURING THIS TIME. A COLD FRONT WILL CROSS THE REGION LATE SUNDAY NIGHT INTO MONDAY MORNING. WESTERLY WINDS WILL MOVE INTO THE REGION BEHIND THE FROPA MONDAY. VFR MON NIGHT-WED W/ NW FLOW 10-20 KTS...GUSTY MON NIGHT INTO TUE THEN DECREASING TO AROUND 10 KTS. && .MARINE... THUNDERSTORMS WILL EXIT THE LOWER CHESAPEAKE BAY THIS AFTERNOON. SOUTHERLY WINDS WILL CONTINUE ON THE WATERS THROUGH SUNDAY NIGHT. SHOWERS AND THUNDERSTORMS WILL MOVE ACROSS THE WATERS SUNDAY AFTERNOON ADN EVENING AHEAD OF A COLD FRONT. STRONG GUSTY WINDS WATERSPOUTS AND LOW VSBYS ARE EXPECTED IN ACTIVITY. SMW`S WILL BE ISSUED IN ACTIVITY THROUGH SUNDAY EVENING. A COLD FRONT WILL CROSS THE WATERS MONDAY MORNING AND SCA WILL BE LIKELY. SCA CONDITIONS POSSIBLE IN GUSTY NW FLOW ASSOCIATED WITH PRESSURE SURGE BEHIND COLD FROPA MON EVE...SUBSIDING TUE THROUGH THU. && .TIDES/COASTAL FLOODING... A LIGHT SOUTHERLY FLOW HAS CAUSED TIDAL ANOMALIES TO INCREASE TO AROUND THREE QUARTERS OF A FOOT ABOVE NORMAL. THIS WILL CAUSE WATER LEVELS TO APPROACH MINOR FLOODING FOR SENSITIVE AREAS NEAR HIGH TIDE SUNDAY MORNING FOR LOCATIONS ALONG THE WESTERN SHORE OF THE MARYLAND CHESAPEAKE BAY AND THE SHORE OF THE UPPER TIDAL POTOMAC RIVER. THE SOUTHERLY FLOW WILL STRENGTHEN A BIT TONIGHT AND THE HIGH TIDE CYCLE LATE TONIGHT INTO SUNDAY MORNING WILL BE THE HIGHER OF THE TWO. MINOR TIDAL FLOODING IS POSSIBLE FOR SENSITIVE AREAS NEAR HIGH TIDE LATE TONIGHT INTO SUNDAY MORNING. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SUNDAY FOR ANZ531>534-537- 539>543. && $$ SYNOPSIS...HAS NEAR TERM...HAS SHORT TERM...HAS LONG TERM...DFH AVIATION...HAS/DFH MARINE...HAS/DFH TIDES/COASTAL FLOODING...HAS

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