Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 111337 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 937 AM EDT THU SEP 11 2014 .SYNOPSIS... A COLD FRONT WILL APPROACH THE AREA FROM THE WEST TODAY BEFORE PASSING THROUGH THE AREA TONIGHT. THE FRONT WILL STALL OUT TO THE SOUTH FRIDAY...BUT IT WILL RETURN NORTH AS A WARM FRONT FRIDAY NIGHT INTO SATURDAY. A REINFORCING COLD FRONT WILL PASS THROUGH THE AREA SATURDAY NIGHT AND HIGH PRESSURE WILL RETURN FOR SUNDAY. ANOTHER COLD FRONT MAY PASS THROUGH THE AREA EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... A COLD FRONT EXTENDS FROM WESTERN NY...ACROSS CENTRAL OHIO AND ALONG THE OHIO RIVER VALLEY THIS MORNING. SOUTHERLY FLOW AHEAD OF THE FRONTAL BOUNDARY WILL CONTINUE TO ADVECT MOISTURE AND WARMER TEMPS INTO THE MID-ATLANTIC REGION. SHOWERS ARE MOVING ALONG AND AHEAD OF THE COLD FRONT CROSSING THE OHIO RIVER VALLEY AND APPALACHIANS THIS MORNING. THESE SHOWERS ARE LIGHT AND SOME ARE DISSIPATING AS THEY MOVE ACROSS THE POTOMAC HIGHLANDS. A BAND OF MID-HIGH CLOUDS WILL MOVE ACROSS THE I-95 CORRIDOR THIS MORNING WHILE CLEARING OCCURS BEHIND AND WEST OF THE BLUE RIDGE AND INTO NORTHERN VA. SHOWERS AND DEBRIS CLOUDS FROM DISSIPATING SHOWERS WILL MOVE INTO THE POTOMAC HIGHLANDS THIS MORNING. THIS WILL BE THE TREND FOR THE MORNING WITH SHOWERS AND CLOUDS MOVING WEST TO EAST ACROSS THE POTOMAC HIGHLANDS AND NORTHERN MARYLAND. THIS WILL LIMIT DESTABILIZATION ACROSS THIS AREA. FURTHER EAST...SUNSHINE AND DESTABILIZATION IS LIKELY FOR THE SHENANDOAH VALLEY AND AREAS EAST OF THE BLUE RIDGE WITH THE EXCEPTION OF FAR NORTHERN MARYLAND WHERE CLOUDS SHOULD BE ALL DAY. PER THE 12Z IAD ROAB...SBCAPE MAY REACH 1500 J/KG TODAY IN PLACES THAT RECEIVE THE MOST SUNSHINE. A REGION OF 30KTS AT 700-850MB WILL ENTER THE REGION THIS AFTERNOON INCREASING THE WIND FIELD. THE WIND FIELD IS EXPECTED TO LAG BEHIND THE BEST INSTABILITY WHICH WILL LIMIT STORMS FROM BECOMING STRONG TO SEVERE. THEREFORE ISOLATED STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND EARLY EVENING. PWAT OF 1.85 INCHES WERE ALSO OBSERVED BY THE 12Z IAD RAOB AND WILL INCREASE BY THIS AFTERNOON. SATELLITE OBS HAVE AROUND 2 INCHES ACROSS THE OHIO VALLEY WHICH WILL BE MOVING INTO THE REGION. THIS DOES POSE A THREAT FOR HEAVY RAINFALL...BUT CURRENT FEELING IS THAT STORMS SHOULD HAVE ENOUGH MOTION TO PREVENT ANY WIDESPREAD THREAT FOR HEAVY RAINFALL. ALSO FLASH FLOOD GUIDANCE IS HIGH...OVER 2 INCHES PER HOUR FOR MOST LOCATIONS. THE COLD FRONT WILL PASS THROUGH THE ENTIRE AREA LATER THIS EVENING INTO THE OVERNIGHT HOURS. COOLER AND DRIER AIR WILL FILTER IN FROM THE NORTH LATE TONIGHT. HOWEVER...THERE IS STILL SOME UNCERTAINTY AS TO HOW FAR SOUTH OF THE AREA THE FRONT WILL MAKE IT. SHOULD THE BOUNDARY GET HUNG UP OVER CENTRAL VIRGINIA...THEN OVERRUNNING MAY BE DEEP ENOUGH FOR MORE CLOUDS AND PERHAPS A FEW SHOWERS ACROSS CENTRAL VIRGINIA AND SOUTHERN MARYLAND. HOWEVER...IF THE FRONT PUSHES FARTHER SOUTH THAN THESE AREAS WILL END UP DRY. EITHER WAY...ANY SHOWERS THAT DO OCCUR WILL BE LIGHT AND MOST OF THE TIME SHOULD BE DRY. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... THE COLD FRONT WILL REMAIN STALLED TO OUR SOUTH FRIDAY AND A NORTHERLY FLOW WILL CONTINUE TO USHER IN COOLER AND DRIER AIR ACROSS MOST LOCATIONS. HOWEVER...MORE CLOUDS AND PERHAPS A FEW SHOWERS ARE POSSIBLE ACROSS CENTRAL VIRGINIA AND SOUTHERN MARYLAND. EVEN ACROSS THESE AREAS...MOST OF THE TIME WILL TURN OUT DRY. MAX TEMPS FRIDAY WILL RANGE FROM THE 60S IN THE MOUNTAINS TO THE MIDDLE 70S NEAR WASHINGTON AND BALTIMORE. HIGH PRESSURE WILL RETREAT TO THE NORTH AND EAST ACROSS NORTHERN NEW ENGLAND WHILE AN AREA OF LOW PRESSURE/TROUGH APPROACH FROM THE SOUTH FRIDAY NIGHT INTO SATURDAY. LIFT ASSOCIATED WITH THIS SYSTEM WILL BRING ABOUT A CHANCE OF SHOWERS DURING THE DAY WITH IMPROVING CONDITIONS SATURDAY NIGHT. UNDER CLOUD COVER...HIGH TEMPERATURES WILL ONLY REACH THE UPPER 60S OVER THE HIGHER TERRAIN OUT WEST TO THE LOWER AND POSSIBLY MIDDLE 70S EAST OF THE BLUE RIDGE AND ACROSS THE METRO AREAS. OVERNIGHT LOWS FROM THE UPPER 40S WEST TO THE UPPER 50S EAST CAN BE EXPECTED. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... HIGH PRESSURE WILL BUILD OVER THE MIDDLE ATLANTIC REGION TO CLOSE THE WEEKEND. PLEASANT WEATHER IS EXPECTED SUNDAY WITH HIGH TEMPERATURES MOSTLY IN THE 70S. ANOTHER TROUGH OF LOW PRESSURE WILL APPROACH THE REGION MONDAY BRINGING INCREASING CLOUDS AND A CHANCE FOR SHOWERS LATER MONDAY INTO TUESDAY. HIGH PRESSURE IS PROGGED BY LONG RANGE GUIDANCE TO RETURN TO THE MIDDLE ATLANTIC FOR THE MIDDLE PART OF NEXT WEEK. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... SHOWERS AND A FEW THUNDERSTORMS ARE LIKELY THIS AFTERNOON AND EARLY EVENING. THUNDERSTORMS WILL HAVE THE POTENTIAL TO PRODUCE GUST WINDS AND LOCALLY HEAVY RAINFALL THAT COULD BRIEFLY REDUCE CIGS/VSBYS TO IFR LEVELS. DRIER AIR WILL MOVE IN BEHIND A COLD FRONT LATER TONIGHT. MOSTLY VFR EXPECTED FRIDAY NIGHT. INCREASING CLOUDS EXPECTED SATURDAY WITH SOME VSBY RESTRICTIONS IN SHOWERS EXPECTED. VFR WILL RETURN FOR SUNDAY THEN SUB-VFR CONDITIONS RETURN LATER MONDAY INTO TUESDAY WITH INCREASING CHANCES FOR SHOWERS. HIGH PRESSURE WILL RETURN FOR THE MIDDLE OF NEXT WEEK. && .MARINE... THE PRESSURE GRADIENT WILL TIGHTEN OVER THE WATERS THROUGH EARLY THIS AFTERNOON AHEAD OF A COLD FRONT. THIS WILL CAUSE SOUTH TO SOUTHWEST WINDS TO STRENGTHEN. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS TODAY. THERE MAY BE A BREAK IN THE GRADIENT WINDS LATER THIS AFTERNOON AND EARLY EVENING...BUT SHOWERS AND THUNDERSTORMS WILL BE AROUND DURING THIS TIME. SOME THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS. A COLD FRONT WILL PASS THROUGH THE WATER LATE THIS EVENING INTO THE OVERNIGHT HOURS AND A PRESSURE SURGE BEHIND THE BOUNDARY WILL CAUSE NORTHERLY WINDS TO INCREASE. THEREFORE...THE SMALL CRAFT ADVISORY CONTINUES THROUGH TONIGHT FOR THE WATERS. THE FLOW WILL GRADUALLY WEAKEN FRIDAY AS THE FRONT STALLS TO OUR SOUTH AND THE PRESSURE GRADIENT WEAKENS. HOWEVER...A SMALL CRAFT ADVISORY IS IN EFFECT FRIDAY MORNING FOR THE MARYLAND CHESAPEAKE BAY SOUTH OF POOLES ISLAND AND THE LOWER TIDAL POTOMAC RIVER. SMALL CRAFT CONDITIONS MAY RETURN SATURDAY NIGHT INTO SUNDAY OVER A PORTION OF THE WATERS ALONG WITH REDUCED VISIBILITY IN SHOWERS. SCA CONDITIONS MAY BE POSSIBLE AT LEAST OVER THE LOWER WATERS TUESDAY NIGHT INTO WEDNESDAY OF NEXT WEEK. && .TIDES/COASTAL FLOODING... SOUTHERLY FLOW HAS CAUSED TIDAL ANOMALIES TO INCREASE TO AROUND 1 TO 1.5 FEET ABOVE NORMAL. THIS WILL CAUSE MINOR TIDAL FLOODING ALONG THE WESTERN SHORE OF THE MARYLAND CHESAPEAKE BAY AND ALONG THE UPPER TIDAL POTOMAC RIVER DURING THE HIGH TIDE CYCLE THIS MORNING INTO EARLY THIS AFTERNOON. THE COASTAL FLOOD ADVISORY REMAINS IN EFFECT FOR THESE AREAS DURING THIS TIME. A COASTAL FLOOD ADVISORY IS ALSO IN EFFECT FOR THE MARYLAND CHESAPEAKE BAY FROM ANNE ARUNDEL COUNTY THROUGH ST MARYS COUNTY FOR THE HIGH TIDE CYCLE LATE THIS AFTERNOON AND EVENING. WATER LEVELS MAY NOT BE AS HIGH AS THIS MORNING SINCE THE FLOW WILL TURN MORE WESTERLY...BUT WATER LEVELS ARE STILL EXPECTED TO EXCEED MINOR FLOODING THRESHOLDS. CERTAINTY FOR MINOR FLOODING THIS EVENING FOR BALTIMORE AND HARFORD COUNTIES ALONG THE WESTERN SHORE OF THE MARYLAND CHESAPEAKE BAY AND THE SHORE OF THE UPPER TIDAL POTOMAC RIVER IS LOWER. THEREFORE...A COASTAL FLOOD ADVISORY HAS NOT BEEN EXTENDED TO INCLUDE THIS TIDE CYCLE...BUT THIS WILL HAVE TO BE MONITORED LATER TODAY. THE OFFSHORE FLOW WILL STRENGTHEN OVERNIGHT BEHIND A COLD FRONT AND TIDAL ANOMALIES WILL DROP SHARPLY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR DCZ001. MD...COASTAL FLOOD ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR MDZ007-013. COASTAL FLOOD ADVISORY UNTIL 10 PM EDT THIS EVENING FOR MDZ014- 017-018. COASTAL FLOOD ADVISORY UNTIL 11 AM EDT THIS MORNING FOR MDZ011. VA...COASTAL FLOOD ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR VAZ054. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL NOON EDT FRIDAY FOR ANZ531>534-537- 539>541-543. SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ530-536-538- 542. SMALL CRAFT ADVISORY UNTIL 6 AM EDT FRIDAY FOR ANZ535. && $$ SYNOPSIS...BJL NEAR TERM...BJL/HAS SHORT TERM...BJL/KRW LONG TERM...BJL/KRW AVIATION...BJL/KRW MARINE...BJL/KRW TIDES/COASTAL FLOODING...BJL

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