Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 232246 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 646 PM EDT SAT AUG 23 2014 .SYNOPSIS... A WEAK COLD FRONT WILL PUSH SOUTH AND WEST THROUGH THE APPALACHIANS THIS EVENING. HIGH PRESSURE WILL BUILD FROM THE CANADIAN MARITIMES DOWN THE COAST...REACHING THE DELMARVA BY SUNDAY...AND REMAINING THROUGH THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH SUNDAY/...
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LATEST ANALYSIS SHOWS HIGH PRESSURE EXTENDING THROUGH NEW ENGLAND. A WEAK COLD FRONT IS LOCATED NEAR THE APPALACHIAN MOUNTAINS AND AN EASTERLY FLOW BEHIND THE BOUNDARY HAS CAUSED MOISTURE TO MOVE IN FROM THE ATLANTIC. THE EASTERLY FLOW WILL CONTINUE ACROSS MOST OF THE AREA THIS EVENING AS THE COLD FRONT SLOWLY MOVES SOUTH AND WEST THROUGH THE APPALACHIAN MOUNTAINS. PLENTY OF MOISTURE REMAINS OVERHEAD DUE TO THE ONSHORE FLOW. ALSO...THE FRONT IS RELATIVELY SHALLOW WHICH MEANS THE 850 MB FRONT IS STILL OVERHEAD. THIS IS PROVIDING ENOUGH FORCING FOR SHOWERS...DESPITE DRIER AIR MOVING IN ALOFT. SHOWERS ARE LIKELY FOR THE REST OF THIS AFTERNOON INTO THIS EVENING AS THE 850MB BOUNDARY REMAINS OVERHEAD. THERE IS SOME CONCERN FOR LOCALLY HEAVY RAINFALL. PWATS ARE DROPPING A BIT AS DRIER AIR MOVES IN ALOFT...BUT PLENTY OF LOW-LEVEL MOISTURE REMAINS. ALSO...WARM RAIN PROCESSES ARE EXPECTED WITH THE LOW- TOPPED CONVECTION. DO NOT FEEL THE THREAT IS WIDESPREAD ENOUGH TO WARRANT A FLASH FLOOD WATCH AT THIS TIME SINCE ANY HEAVY RAIN WILL BE LOCALIZED AND FLASH FLOOD GUIDANCE REMAINS HIGH ACROSS MOST AREAS. THE COLD FRONT WILL MOVE WEST OF OUR AREA TONIGHT AND THE SURFACE HIGH OVER NEW ENGLAND WILL PUSH FARTHER SOUTH AND WEST INTO OUR AREA. DRIER AIR WILL MOVE IN FROM THE NORTH AND EAST...CAUSING THE PRECIPITATION SHIELD TO SHIFT WEST INTO CENTRAL VIRGINIA AND THE POTOMAC HIGHLANDS. DRIER CONDITIONS ARE EXPECTED ACROSS THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS. LOW CLOUDS AND AREAS OF FOG ARE EXPECTED AS LOW-LEVEL MOISTURE GETS TRAPPED UNDERNEATH THE NOCTURNAL INVERSION. MIN TEMPS WILL RANGE FROM THE UPPER 50S AND LOWER 60S IN THE MOUNTAINS TO THE MIDDLE 60S IN DOWNTOWN WASHINGTON AND BALTIMORE.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE AREA SUNDAY...ALLOWING FOR DRIER AIR TO MOVE IN FROM THE NORTH AND EAST. A FEW MORNING SHOWERS ARE POSSIBLE ACROSS CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS...BUT EVEN ACROSS THESE AREAS SUNDAY AFTERNOON SHOULD TURN OUT DRY. MAX TEMPS WILL RANGE FROM THE UPPER 60S AND LOWER 70S IN THE MOUNTAINS TO NEAR 80 IN WASHINGTON AND BALTIMORE. NICE STRETCH OF WEATHER COMING UP SUNDAY NIGHT THROUGH WEDNESDAY AS POSITIVELY TILTED UPPER RIDGE DOMINATES THE UPPER PATTERN OVERHEAD. SURFACE HIGH PRESSURE BUILDING IN BEHIND BACKDOOR COLD FRONT...AND PWATS UNDER ONE INCH WILL RESULT IN LOW HUMIDITY WITH LIGHT WINDS AND BELOW NORMAL TEMPERATURES THROUGH EARLY WEEK. TEMPS AND HUMIDITY BEGIN TO MODERATE BY WEDNESDAY AS UPPER RIDGE NUDGES EASTWARD. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... NICE STRETCH OF WEATHER COMING UP SUNDAY NIGHT THROUGH WEDNESDAY AS POSITIVELY TILTED UPPER RIDGE DOMINATES THE UPPER PATTERN OVERHEAD. SURFACE HIGH PRESSURE BUILDING IN BEHIND BACKDOOR COLD FRONT...AND PWATS UNDER ONE INCH WILL RESULT IN LOW HUMIDITY WITH LIGHT WINDS AND BELOW NORMAL TEMPERATURES THROUGH EARLY WEEK. TEMPS AND HUMIDITY BEGIN TO MODERATE BY WEDNESDAY AS UPPER RIDGE NUDGES EASTWARD. TROUGH PROGRESSING ACROSS THE NORTHERN CONUS LATE IN THE WEEK IS NOW SLOWER THAN PREVIOUS RUNS WHICH BRINGS THE TRACK OF TROPICAL SYSTEM FARTHER WEST ON BACKSIDE OF MID-LEVEL UPPER RIDGE FLOW. CURRENT TRACK IS STILL WELL OFFSHORE TO THE SOUTHEAST OF THE MID-ATLANTIC LATE IN THE WEEK BUT UNCERTAINTY EXISTS ATTM. AFOREMENTIONED UPPER TROUGH WILL THEN DRAG A SURFACE COLD FRONT EASTWARD ACROSS THE REGION NEXT WEEKEND WITH DEEP LAYER SHEAR AND INSTABILITY PROFILES LOOKING FAVORABLE FOR SOME ORGANIZED CONVECTION. FROPA TIMING DIFFERENCE STILL PRESENT BETWEEN EXTENDED MODELS HOWEVER...WITH THE EURO MUCH LESS PROGRESSIVE. TEMPERATURES WILL CLIMB BACK TO NEAR NORMAL AHEAD OF THE THIS FRONT AS RETURN FLOW SETS IN THURSDAY AND FRIDAY. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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SHOWERS ARE MOVING TO THE SOUTH AND EAST...AND GENERALLY AWAY FROM THE TERMINALS EARLY THIS EVENING. MOSTLY MVFR CEILINGS...WITH PERIODIC IFR POSSIBLE. ON THE OTHER SIDE OF THE COIN...LOWEST CLOUD DECK MAY SCATTER OUT AT TIMES WITH OCCASIONAL VFR. AN EASTERLY FLOW IS EXPECTED TONIGHT...BUT SOME DRIER AIR WILL PUSH IN AS HIGH PRESSURE BUILDS INTO OUR AREA. LOW CLOUDS AND AREAS OF FOG ARE EXPECTED UNDERNEATH THE NOCTURNAL INVERSION FOR THE WESTERN TERMINALS. THE LOW CLOUDS MAY MAKE IT INTO THE EASTERN TERMINALS...BUT CONFIDENCE IS LESS. ANY LOW CLOUDS AND FOG WILL BURN OFF SUNDAY MORNING. HIGH PRESSURE WILL PREVAIL THROUGH MID WEEK BEFORE A COLD FRONT APPROACHES FRIDAY.
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&& .MARINE... A PRESSURE SURGE IS EXPECTED BEHIND A COLD FRONT TONIGHT. THIS WILL CAUSE WIND GUSTS AROUND SCA CRITERIA FOR THE MARYLAND CHESAPEAKE BAY SOUTH OF POOLES ISLAND AND THE LOWER TIDAL POTOMAC RIVER. A SMALL CRAFT ADVISORY IS IN EFFECT TONIGHT UNTIL 10 AM SUNDAY MORNING FOR THESE AREAS. ELSEWHERE...WIND GUSTS HAVE BEEN CAPPED AT 10 TO 15 KNOTS. HIGH PRESSURE WILL THEN BUILD ACROSS THE AREA THROUGH MID WEEK BEFORE A COLD FRONT APPROACHES FRIDAY. WINDS LOOK TO STAY BELOW SCA LEVELS. && .TIDES/COASTAL FLOODING...
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A COASTAL FLOOD ADVISORY HAS BEEN ISSUED FOR ALEXANDRIA...WITH MINOR INUNDATION EXPECTED AROUND HIGH TIDE THIS EVENING. AT WASHINGTON CHANNEL...ANOMALIES WERE RISING LATE THIS AFTERNOON BUT HAVE LEVELED OFF EARLY THIS EVENING. IT IS EXPECTED THAT HIGH TIDE THIS EVENING WILL FALL SHORT OF MINOR INUNDATION BY AROUND ONE TENTH OF A FOOT. ANOTHER COASTAL FLOOD ADVISORY IS IN EFFECT FOR THE WESTERN SHORE OF THE CHESAPEAKE BAY AND THE UPPER TIDAL POTOMAC FOR HIGH TIDE LATE TONIGHT INTO SUNDAY MORNING. THIS IS THE HIGHER OF THE TWO DAILY HIGH TIDE CYCLES...AND ANOMALIES SHOULD BE AROUND ONE FOOT OR SLIGHTLY HIGHER. THE EASTERLY FLOW WILL CONTINUE INTO MONDAY. THE HIGH TIDE CYCLE LATE SUNDAY NIGHT INTO MONDAY MORNING MAY CAUSE MORE MINOR TIDAL FLOODING FOR SENSITIVE LOCATIONS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT SUNDAY FOR DCZ001. MD...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT SUNDAY FOR MDZ011-014-017-018. VA...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT SUNDAY FOR VAZ054. COASTAL FLOOD ADVISORY UNTIL 9 PM EDT THIS EVENING FOR VAZ054. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EDT SUNDAY FOR ANZ531>534-537- 539>541-543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...AEB LONG TERM...AEB AVIATION...BJL/AEB/KCS MARINE...BJL/AEB TIDES/COASTAL FLOODING...KCS

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