Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231811 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 211 PM EDT SAT AUG 23 2014 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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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 AFTERNOON AND 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 WARRENT 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 THROUGH WEDNESDAY/...
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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.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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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.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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SHOWERS ARE LIKELY THIS AFTERNOON INTO THIS EVENING WITH MVFR CIGS FOR MOST OF THE TIME. BRIEF IFR CONDITIONS CANNOT BE RULED OUT IN HEAVIER SHOWERS. 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...
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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.
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&& .TIDES/COASTAL FLOODING...
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A PERSISENT ONSHORE FLOW HAS CAUSED TIDAL ANOMALIES TO RISE TO AROUND ONE FOOT ABOVE NORMAL. THE PM TIDE TODAY IS THE LOWER OF THE TWO ASTRONOMICALLY...BUT WITH THE FCST WATER LVL INCREASE SHOULD END UP BEING SIMILAR TO THE MRNG TIDE...IF NOT A PINCH HIGHER. THE CONCERN COMES LATE TNGT INTO SUN MRNG...WHEN DEPARTURES OF A FOOT WL CAUSE WATER TO APPROACH MINOR THRESHOLDS FOR SENSITIVE LOCATIONS ON THE WESTERN SHORE AND UPPER TIDAL POTOMAC. A COASTAL FLOOD ADVISORY IS IN EFFECT DURING THIS TIME. 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. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 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 MARINE...BJL/AEB TIDES/COASTAL FLOODING...BJL

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