Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 181810 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 210 PM EDT THU SEP 18 2014 .SYNOPSIS... A WEAK COLD FRONT WILL PASS THROUGH THIS AFTERNOON AND EVENING. HIGH PRESSURE WILL BUILD OVERHEAD FOR LATE TONIGHT THROUGH SATURDAY. THE HIGH WILL MOVE OFF THE COAST SUNDAY AND A STRONGER COLD FRONT WILL PASS THROUGH THE AREA SUNDAY NIGHT INTO MONDAY. HIGH PRESSURE WILL RETURN FOR THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH FRIDAY/... A BROAD UPPER-LEVEL TROUGH WILL REMAIN OVER THE REGION THROUGH LATE THIS AFTERNOON AND EVENING WHILE A WEAK UPPER-LEVEL DISTURBANCE PASSES THROUGH IN THE FLOW ALOFT. A WEAK COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL ALSO MOVE THROUGH DURING THIS TIME. DESPITE LIMITED MOISTURE AND FORCING...THERE HAS BEEN ENOUGH WARM AIR FOR A LITTLE INSTABILITY AHEAD OF THE BOUNDARY...CAUSING A FEW SHOWERS TO DEVELOP NEAR THE INTERSTATE 95 CORRIDOR INTO CENTRAL VIRGINIA. THE THREAT FOR SHOWERS WILL CONTINUE INTO EARLY THIS EVENING...BUT COVERAGE WILL BE ISOLATED WITH MOST AREAS REMAINING DRY. THE COLD FRONT WILL DROP TO OUR SOUTH LATE TONIGHT AND HIGH PRESSURE WILL BUILD OVER NEW ENGLAND...ALLOWING FOR THE SURFACE RIDGE AXIS ASSOCIATED WITH THIS HIGH TO BUILD INTO OUR AREA. THIS SHOULD BRING DRY CONDITIONS OVERNIGHT...BUT CLOUDS MAY GET HUNG UP ACROSS CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS WHERE OVERRUNNING WILL OCCUR BEHIND THE COLD FRONT. HIGH PRESSURE WILL CONTINUE TO WEDGE INTO THE MID-ATLANTIC THROUGH FRIDAY...BRINGING MAINLY DRY CONDITIONS ALONG WITH BELOW NORMAL TEMPERATURES. HOWEVER...THE FLOW WILL TURN ONSHORE AND THIS MAY CAUSE CLOUDS TO GET TRAPPED UNDERNEATH THE SUBSIDENCE INVERSION. THE DEEPEST MOISTURE WILL BE ACROSS SOUTHERN MARYLAND...CENTRAL VIRGINIA AND THE POTOMAC HIGHLANDS WHERE A FEW SPRINKLES CANNOT BE RULED OUT. MAX TEMPS WILL RANGE FROM THE LOWER TO MIDDLE 60S IN THE POTOMAC HIGHLANDS TO THE LOWER AND MIDDLE 70S NEAR WASHINGTON AND BALTIMORE. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... HIGH PRESSURE WILL MOVE OFF THE NEW ENGLAND COAST AND THE SURFACE RIDGE AXIS WILL CONTINUE TO EXTEND SOUTH AND WEST TOWARD THE MID- ATLANTIC COAST FRIDAY NIGHT THROUGH SATURDAY. AN ONSHORE FLOW WILL CONTINUE DURING THIS TIME...AND IT MAY LEAD TO SOME LOW CLOUDS ALONG WITH PATCHY FOG...ESPECIALLY LATE FRIDAY NIGHT INTO SATURDAY MORNING. CLOUDS SHOULD GIVE WAY TO SUNSHINE SATURDAY...AND THAT WILL CAUSE MAX TEMPS TO BE A BIT WARMER COMPARED TO FRIDAY...RANGING FROM THE 70S IN THE MOUNTAINS TO NEAR 80 ACROSS WASHINGTON AND BALTIMORE. A STRONGER COLD FRONT WILL APPROACH THE AREA SATURDAY NIGHT...BUT THE SURFACE RIDGE AXIS SHOULD REMAIN IN PLACE. AREAS OF LOW CLOUDS AND FOG ARE POSSIBLE OVERNIGHT SATURDAY INTO SUNDAY MORNING. THE COLD WILL MOVE INTO THE AREA SUNDAY AFTERNOON. A SOUTHERLY FLOW AHEAD OF THE FRONT WILL CAUSE WARM AND HUMID CONDITIONS. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE SUNDAY AFTERNOON AHEAD OF THE COLD FRONT. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... A COLD FRONT WILL MOVE ACROSS THE REGION TO THE EAST COAST SUNDAY NIGHT. THERE IS A CHANCE FOR SHOWERS ALONG THE FRONT...MAINLY FROM THE SHENANDOAH VALLEY EAST TO THE CHESAPEAKE BAY. AN UPPER LEVEL TROUGH OF LOW PRESSURE WILL SWEEP ACROSS THE REGION MONDAY. THERE COULD BE A FEW INSTABILITY SHOWERS THAT DEVELOP ENLIGHTEN TO THIS TROUGH. FOR THE MOST PART...MOST AREAS SHOULD BE DRY. HIGH PRESSURE WILL GRADUALLY BUILD INTO THE REGION MONDAY NIGHT. HIGH PRESSURE SHOULD HANG ON TO THE MID ATLANTIC COAST TUESDAY BEFORE IT MOVES OFFSHORE AND A SURFACE COLD FRONT SAGS IN FROM THE NORTHWEST AND NORTH LATE TUESDAY INTO TUESDAY NIGHT. WITH LIMITED MOISTURE IN PLACE...MOST AREAS WILL BE RAINFREE. A SECOND AREA OF HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT AND USHER IN COLDER THAN NORMAL AIR INTO THE REGION WEDNESDAY THROUGH THURSDAY. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... VFR CONDITIONS ARE EXPECTED THIS AFTERNOON AND EVENING. A STRAY SHOWER CANNOT BE RULED OUT...BUT MOST AREAS WILL BE DRY. AN ONSHORE FLOW WILL DEVELOP LATE TONIGHT THROUGH FRIDAY...AND THIS MAY LEAD TO LOW CLOUDS ACROSS KCHO. ALSO PATCHY BR IS POSSIBLE LATE TONIGHT INTO FRIDAY MORNING FOR KMRB AND KCHO. VFR CONDITIONS ARE EXPECTED FOR MOST OF THE TERMINALS FRIDAY...BUT LOW CLOUDS MAY PERSIST ACROSS KCHO WHICH COULD LEAD TO MVFR CONDITIONS. LOW CLOUDS MAY BECOME MORE WIDESPREAD LATE FRIDAY NIGHT INTO SATURDAY...AND AGAIN LATE SATURDAY NIGHT INTO SUNDAY AS AN ONSHORE FLOW PERSISTS. A COLD FRONT WILL MOVE INTO THE TERMINALS SUNDAY AFTERNOON...AND A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE. && .MARINE... A WEAK COLD FRONT WILL PASS THROUGH THE WATERS LATE THIS AFTERNOON AND EVENING. A COUPLE SHOWERS ARE POSSIBLE...BUT MOST AREAS WILL BE DRY. A PRESSURE SURGE IS EXPECTED TO DEVELOP BEHIND THE COLD FRONT LATE TONIGHT THROUGH FRIDAY MORNING. THIS WILL CAUSE WINDS TO INCREASE AND A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER. HOWEVER...IT WILL BE MARGINAL WITH GUSTS NEAR 20 KNOTS. AN EAST TO SOUTHEAST FLOW WILL CONTINUE FRIDAY THROUGH SATURDAY AS HIGH PRESSURE BUILDS OFF THE NEW ENGLAND COAST. WIND GUSTS MAY APPROACH SCA CRITERIA AT TIMES...BUT THE GUSTS HAVE BEEN CAPPED AT 15 KNOTS FOR NOW DUE TO A RELATIVELY WEAK PRESSURE GRADIENT. A COLD FRONT WILL APPROACH THE WATERS SUNDAY. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE LATE IN THE DAY INTO SUNDAY NIGHT. WINDS WILL SHIFT TO THE NORTHWEST BEHIND THE FRONT...AND A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS SUNDAY NIGHT INTO MONDAY. && .TIDES/COASTAL FLOODING... TIDAL ANOMALIES HAVE INCREASED TO ABOUT 1 TO 1.5 FEET ABOVE NORMAL FROM THE SOUTHERLY FLOW WEDNESDAY. THE FLOW WILL BE CONTINUE TO BE LIGHT THROUGH THIS EVENING...BEFORE INCREASING AND TURNING TOWARD THE NORTHEAST LATE TONIGHT. WITH NO OFFSHORE FLOW TO PUSH THE WATER OUT OF THE BAY...THESE TIDAL ANOMALIES ARE LIKELY TO CONTINUE THROUGH TONIGHT. A COASTAL FLOOD ADVISORY IS IN EFFECT FOR THE HIGH TIDE CYCLE LATE TONIGHT INTO EARLY FRIDAY FOR ANNE ARUNDEL COUNTY THROUGH ST MARYS COUNTY. ELSEWHERE...MINOR TIDAL FLOODING IS POSSIBLE NEAR HIGH TIDE LATE TONIGHT INTO EARLY FRIDAY. HOWEVER...CONFIDENCE IS NOT HIGH ENOUGH FOR A COASTAL FLOOD ADVISORY AT THIS POINT. AN ONSHORE FLOW IS EXPECTED TO CONTINUE THROUGH SUNDAY...CAUSING ELEVATED WATER LEVELS AND THE POSSIBILITY OF MINOR TIDAL FLOODING. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...COASTAL FLOOD ADVISORY FROM 8 PM THIS EVENING TO 2 AM EDT FRIDAY FOR MDZ017-018. COASTAL FLOOD ADVISORY UNTIL 5 AM EDT FRIDAY FOR MDZ014. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 AM TO NOON EDT FRIDAY FOR ANZ530>534-537-539>541-543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...BJL/KLW AVIATION...BJL/KLW MARINE...BJL/KLW TIDES/COASTAL FLOODING...BJL

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