Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 101845 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 245 PM EDT WED SEP 10 2014 .SYNOPSIS...
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A COLD FRONT WILL APPROACH THE AREA FROM THE WEST TONIGHT. THE BOUNDARY WILL MOVE THROUGH THE MID-ATLANTIC BY THURSDAY NIGHT BEFORE STALLING OUT TO THE SOUTH FRIDAY THROUGH SATURDAY. A REINFORCING COLD FRONT WILL PASS THROUGH THE AREA SATURDAY NIGHT AND HIGH PRESSURE WILL RETURN FOR SUNDAY.
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&& .NEAR TERM /THROUGH THURSDAY/...
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HIGH PRESSURE IS LOCATED OVER THE MID ATLANTIC REGION THIS AFTERNOON. COASTAL LOW PRESSURE OFF THE COAST OF THE DELMARVA WILL MOVE EAST AND AWAY FROM THE REGION. ANOTHER AREA OF LOW PRESSURE ACROSS WISCONSIN WILL CONTINUE TO DEEPEN AS IT MOVES NORTHEASTWARD TODAY. HIGH PRESSURE OVER THE REGION HAS LED TO SLOW MIXING ACROSS THE REGION. A MARINE AIRMASS IS SLOWLY DISSIPATING AS WINDS BECOME SOUTHERLY THIS AFTERNOON. TEMPS HAVE BEEN SLOWER TO RISE TODAY DUE TO THE CLOUD COVER AND AREAS IN THE WESTERN DC/BALTIMORE SUBURBS ARE STILL IN THE LOW 70S AS OF 2PM. CLOUDS ARE EXPECTED TO DISSIPATE TODAY ALBEIT SLOWLY. SUNSHINE SHOULD BREAK THROUGH BY LATE AFTERNOON. HIGH PRESSURE WILL MOVE OFF THE COAST OVERNIGHT AND SOUTHERLY FLOW AT THE SFC WILL INTENSIFY AHEAD OF DEEPENING LOW PRESSURE ACROSS THE GREAT LAKES. THIS WILL DRAW IN MOISTURE INTO THE MID-ATLANTIC AND FCST MIN TEMPS ARE EXPECTED TO BE IN THE MID TO UPPER 60S BY THURSDAY MORNING DUE TO THE MID 60S DEWPTS. WINDS ALOFT WILL CONTINUE TO STRENGTHEN AS A COLD FRONT APPROACHES FROM THE OHIO VALLEY. AT THE SFC...SOUTHERLY WINDS 5-10 MPH OVERNIGHT WILL HALT FOG FORMATION. MID TO HIGH LEVEL DEBRIS CLOUDS WILL BE ACROSS THE AREA BY THURSDAY MORNING AS A COLD FRONT APPROACHES THE POTOMAC HIGHLANDS. SOUTHERLY FLOW WILL CONTINUE AT THE SFC AND CONTINUE TO DRAW IN MOISTURE WITH DEWPTS RISING INTO THE LOW 70S BY AFTERNOON. FCST MAX TEMPS WILL RANGE FROM THE MID TO UPPER 80S EAST OF THE BLUE RIDGE TO THE UPPER 70S IN THE MTNS. CLOUD COVER ACROSS THE REGION WILL LIMIT INSTABILITY AND SBCAPE OF 800-1500 J/KG IS EXPECTED DEPENDING ON THE CLOUD COVER. AS THE WIND FIELD INCREASES ALOFT 20-30KTS OF EFF 0-6KM SHEAR IS EXPECTED. DUE TO THE HIGH DEWPTS AND MARGINAL SHEAR/INSTABILITY...STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE THURSDAY AFTERNOON AND EVENING. THE COLD FRONT IS EXPECTED TO BE NEAR THE BLUE RIDGE BY EARLY AFTERNOON AND THE I-95 CORRIDOR BY EARLY EVENING. SOME STORMS AHEAD OF THE COLD FRONT MAY PRODUCE DAMAGING WINDS. PWATS ALONG AND AHEAD OF THE COLD FRONT ARE PROGGED TO BE NEAR 2-2.25 INCHES AND HEAVY RAIN IS EXPECTED. AT THIS TIME...DUE TO THE PROGGED QUICKER STORM MOTION FLASH FLOODING IS NOT EXPECTED AT THIS TIME.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
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THE COLD FRONT IS EXPECTED TO MOVE ACROSS THE REGION THURSDAY NIGHT. THE LATEST 12Z MODEL SOLUTIONS FROM THE GFS...NAM AND THE 9Z SREF MEAN HAVE THE FRONT MOVING INTO THE TIDEWATER REGION OF VA BY EARLY FRIDAY MORNING. NORTHERLY WINDS BEHIND THE FRONT WILL LEAD TO DRIER COOLER AIR ENTERING THE MID-ATLANTIC FRIDAY. FCST MAX TEMPS WILL RANGE FROM THE LOW TO MID 70S NEAR THE PA/MD BORDER TO THE MID TO UPPER 70S IN THE NRN PIEDMONT/SRN MD. THE COLD FRONT WILL STALL ACROSS THE CAROLINAS WHILE A SHORTWAVE TROUGH MOVES INTO THE UPPER MID-WEST. THE STALLED BOUNDARY IS EXPECTED TO MOVE NORTHWARD DUE TO LOW PRESSURE MOVING INTO THE GREAT LAKES REGION. SHOWERS ARE POSSIBLE ACROSS THE CENTRAL FOOTHILLS BY SATURDAY MORNING. SHOWERS MAY OVERSPREAD THE REGION SATURDAY RESULTING IN A CLOUDY DAY WITH SCT SHOWERS. FCST MAX TEMPS WILL RANGE FROM THE UPPER 60S WEST OF THE BLUE RIDGE TO THE LOW 70S ALONG THE I-95 CORRIDOR. TEMPS IN THE MID 60S ARE EXPECTED AT HIGHER ELEVATIONS.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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ECMWF 500MB HAS WEAK TROUGH CROSSING THE CWA SATURDAY NIGHT THEN ZONAL FLOW THROUGH TUESDAY. SURFACE HIGH PRESSURE BUILDING ACROSS CWA SATURDAY NIGHT WILL MOVE OFFSHORE BY MONDAY EVENING. SLIGHT CHANCE OF SHOWERS EAST OF THE BLUE RIDGE. MOIST CONDITIONS WILL RETURN ON SOUTH TO SOUTHWEST FLOW AROUND THE BACK OF HIGH MONDAY AFTERNOON. INCRASING CHANCE OF RAIN IN THE VIRGINIA PIEDMONT AND THE CENTRAL SHENANDOAH VALLEY MONDAY AFTERNOON WILL SPREAD ACROSS THE REST OF CWA MONDAY NIGHT. A BOUNDARY WILL CROSS THE CWA EARLY TUESDAY TAKING THE PRECIPITATION OFFSHORE. HIGH PRESSURE AND MUCH DRIER CONDITIONS WILL RETURN FOR MUCH OF TUESDAY AND WEDNESDAY.
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&& .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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SOUTHERLY FLOW AT THE SFC HAS LED TO CLOUDS DISSAPATING ACROSS THE REGION AND VFR CONDITIONS ARE EXPECTED THIS AFTERNOON AND EVENING. SOUTHERLY FLOW SHOULD STAY 5-10 KTS OVERNIGHT AND FOG DEVELOPEMENT IS NOT EXPECTED. MVFR CIGS ARE POSSIBLE AT CHO-IAD-MRB EARLY THURSDAY MORNING. A COLD FRONT WILL CROSS THE REGION THURSDAY. SHRA AND TSRA ARE EXPECTED AND WILL LIKELY REDUCE TAF SITES TO IFR IN ACTIVITY. GUSTY WINDS AND HEAVY RAIN ARE LIKELY. WINDS WILL BECOME NRLY BEHIND THE FRONTAL BOUNDARY AS IT MOVES WEST TO EAST ACROSS THE REGION THURSDAY AFTERNOON AND EVENING. THE FRONTAL BOUNDARY WILL LIKELY MOVE NORTHWARD FRIDAY NIGHT AND SATURDAY AND SHRA ARE POSSIBLE. MVFR/IFR CONDITIONS POSSIBLE DURING THIS TIME.
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&& .MARINE...
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VARIABLE WINDS WILL CONTINUE ON THE WATERS TODAY BEFORE BECOMING SOUTHERLY THIS EVENING. WINDS ARE EXPECTED TO STAY BELOW SCA CRITERIA. SOUTHERLY WINDS WILL CHANNEL UP THE BAY THURSDAY AFTERNOON AND SCA ARE MARGINAL. AT THIS TIME...CONFIDENCE IS LOW TO ISSUE AN ADVISORY. A COLD FRONT WILL CROSS THE WATERS THURSDAY EVENING AND NRLY WINDS WILL MOVE INTO THE REGION. SCA CONDITIONS ARE POSSIBLE IN POST- FRONTAL CONDITIONS. AT THIS TIME DUE TO UNCERTAINITY IN THE TIMING OF THE FRONTAL BOUNDARY...NO SCA IS IN EFFECT. SHOWERS AND THUNDERSTORMS ARE EXPECTED NEAR THE FRONT AND GUSTY WINDS MAY LEAD TO SMW`S ON THE LATE THURS AFTERNOON TO LATE THURS NIGHT.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMOLIES ARE AROUND ONE FOOT ABOVE NORMAL ON THE WESTERN SHORE OF THE BAY AND UPPER TIDAL POTOMAC. A COASTAL FLOOD ADVISORY IS IN EFFECT FOR THE DC/ALEXANDIA WATERFRONT THROUGH THURSDAY AROUND HIGH TIDE. A COASTAL FLOOD ADVISORY IS IN EFFECT FOR THE WESTERN SHORE OF THE CHESAPEAKE BAY FROM BALTIMORE COUNTY TO ST.MARYS COUNTY THROUGH THRUSDAY MIDDAY. WINDS HAVE BECOME SOUTHEASTERLY IN MANY AREAS ALBEIT LIGHT. WINDS ARE EXPECTED TO INCREASE AND BECOME ONSHORE THROUGH THURSDAY. WATER DID NOT EXIT THE BAY WHILE LIGHT THIS AFTERNOON AND THEREFORE ANOMALIES WILL STILL BE AROUND ONE FOOT ABOVE NORMAL. SOUTHERLY WINDS WILL THEN INCREASE TONIGHT AND ANOMALIES WILL RISE TO A FOOT TO FOOT AND HALF BY THURSDAY MORNING. AN OFFSHORE FLOW BEHIND THE COLD FRONT WILL CAUSE ANOMALIES TO SHARPLY DROP LATE THURSDAY NIGHT AND FRIDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 2 PM EDT THURSDAY FOR DCZ001. MD...COASTAL FLOOD ADVISORY UNTIL 11 AM EDT THURSDAY FOR MDZ011-014- 017-018. COASTAL FLOOD ADVISORY UNTIL 2 PM EDT THURSDAY FOR MDZ013. VA...COASTAL FLOOD ADVISORY UNTIL 2 PM EDT THURSDAY FOR VAZ054. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HAS NEAR TERM...HAS SHORT TERM...HAS LONG TERM...CEM AVIATION...HAS MARINE...HAS TIDES/COASTAL FLOODING...HAS

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