Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231351 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 951 AM EDT WED APR 23 2014 .SYNOPSIS... HIGH PRESSURE WILL SLOWLY BUILD OVER THE AREA THROUGH THURSDAY. A COLD FRONT WILL PASS THROUGH THE AREA FRIDAY AND ANOTHER COLD FRONT IS EXPECTED TO MOVE THROUGH SATURDAY. HIGH PRESSURE WILL BUILD OVERHEAD SUNDAY AS THE COLD FRONT STALLS TO OUR SOUTH. WAVES OF LOW PRESSURE WILL DEVELOP ALONG THE STALLED BOUNDARY...BRINGING UNSETTLED CONDITIONS TO THE AREA NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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1023 MB SFC HIGH LOCATED OVER THE UPPER MIDWEST/GREAT LAKES WHILE A COLD FRONT STETCHES FROM A 995 MB SFC LOW OVER MAINE SOUTHWESTWARD TOWARD THE SERN ATLANTIC COAST. A RELATIVELY STRONG PRESSURE GRADIENT BETWEEN THESE SYSTEMS WILL RESULT IN A BREEZY DAY. STRONG CAA ON THE BACKSIDE OF THE LOW HAS RESULTED IN A WELL-MIXED BOUNDARY LAYER UP TO 800 MB AS SEEN ON THE 12Z IAD RAOB SOUNDING. ACCORDINGLY WINDS WILL PICK UP QUICKLY THIS MRNG...RESULTING IN GUSTS OF 30-40 MPH FOR MUCH OF TDA. CAA PATTERN HAS PRODUCED STRATOCU AS MOISTURE AT THE TOP OF THE MIXED LAYER IS TRAPPED BELOW THE SUBSIDENCE INVERSION FIELD. UPDATED SKY COVER FCST GRIDS USING THE RH FIELD AT THE TOP OF THE MIXING LAYER FROM THE RAP TO ACCOUNT FOR THE EVOLUTION OF STRATOCU TDA. PARTLY SUNNY TO MOSTLY CLOUDY SKIES CAN BE EXPECTED ACROSS THE NRN HALF OF THE CWA THIS MRNG BEFORE CLOUDS ERODE FROM S TO N INTO THE AFTN. LOWERED MAX TEMPS A COUPLE OF DEGREES NEAR THE MASON-DIXON LINE TO THE UPPER 50S...WHERE CLOUD COVER MAY HOLD ON THE LONGEST. OTHERWISE...OFFICIAL MAX TEMP FCST IN LOW TO MID 60S FALLS ON THE WARMER SIDE OF GUIDANCE WITH STRONG HEATING AND DOWNSLOPING FLOW. ONCE THE UPPER VORT COMPLETELY MOVES OFF THE COAST SLOWLY TNGT... WINDS WILL DROP OFF OVER THE WRN HALF OF THE REGION. NERN MD WILL REMAIN THE SOME OF THE BREEZIER CONDITIONS LATE TONIGHT... SINCE THE RIBBON OF UPPER VORTICITY WILL STILL BE HANGING OUT OVER DELMARVA - VERY SLOWLY DRIFTING TOWARD THE COAST. A DAY`S WORTH OF DRY AIR WILL ALLOW TEMPS TO DROP BACK DOWN AGAIN INTO THE M-U30S FOR OVERNIGHT LOWS. A FEW AREAS OF THE CWA LIKE THE APLCNS AND SHEN VLY WILL SEE TEMPS HOVERING AROUND FREEZING.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... SURFACE HIGH PRESSURE WILL BUILD OVER THE REGION THURSDAY WHILE AN UPPER-LEVEL RIDGE MOVES OVERHEAD DURING THIS TIME. PLENTY OF SUBSIDENCE WILL ALLOW FOR DRY CONDITIONS ALONG WITH SUNSHINE. MAX TEMPS WILL BE NEAR CLIMO...RANGING FROM THE 50S IN THE MOUNTAINS TO THE MID AND UPPER 60S ACROSS MOST OTHER LOCATIONS. SOME AREAS ACROSS CENTRAL VIRGINIA AND THE VALLEYS OF EASTERN WEST VIRGINIA MAY REACH INTO THE 70S. THE SURFACE HIGH AND UPPER-LEVEL RIDGE AXIS WILL SLIDE TO THE EAST THURSDAY NIGHT AND A COLD FRONT WILL APPROACH FROM THE OHIO VALLEY. CLOUDS ASSOCIATED WITH THIS SYSTEM WILL OVERSPREAD THE AREA...BUT PRECIPITATION SHOULD HOLD OFF UNTIL FRIDAY. MIN TEMPS WILL RANGE FROM THE LOWER TO MIDDLE 40S ACROSS MOST LOCATIONS TO NEAR 50 IN DOWNTOWN WASHINGTON AND BALTIMORE. && .LONG TERM /FRIDAY THROUGH TUESDAY/... A COLD FRONT WILL PASS THROUGH THE REGION FRIDAY...BRINGING A FEW SHOWERS WITH IT. AN ISOLATED THUNDERSTORM CANNOT BE RULED OUT...BUT INSTABILITY WILL BE LIMITED SO ANY SEVERE THREAT SHOULD REMAIN WELL TO OUR SOUTH. THE BOUNDARY WILL MOVE EAST FRIDAY NIGHT ALLOWING FOR DRY CONDITIONS...BUT ANOTHER COLD FRONT WILL PASS THROUGH THE REGION SATURDAY AFTERNOON. LITTLE MOISTURE WILL BE ASSOCIATED WITH THIS SO MOST AREAS WILL LIKELY REMAIN DRY. SATURDAY WILL TURN OUT MILD AHEAD OF THE BOUNDARY DUE TO A DOWNSLOPING WESTERLY FLOW AHEAD OF THE FRONT. CANADIAN HIGH PRESSURE WILL BUILD OVERHEAD SATURDAY NIGHT THROUGH SUNDAY BEHIND THE FRONT...BRINGING DRY AND COOLER CONDITIONS. CUTOFF LOW PRESSURE WILL TRACK THROUGH THE PLAINS INTO THE MIDWEST NEXT WEEK. A WARM FRONT WILL STALL OUT NEAR THE REGION DURING THIS TIME AND UNSETTLED CONDITIONS ARE POSSIBLE. CERTAINTY IN THE FORECAST REMAINS LOW AT THIS TIME. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
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GUSTY NW WINDS WILL BE THE MAIN WX STORY TDA FOR THE AREA TERMINALS. NW WINDS HAVE QUICKLY PICKED UP THIS MRNG WITH GUSTS 25-35 KT ALREADY BEING REPORTED AT 13Z. EXPECT GUSTS OF THIS MAGNITUDE TO CONTINUE THRU AFTN BEFORE GRADUALLY SUBSIDING TOWARD SUNSET THIS EVE. BKN STRATOCU FIELD BETWEEN 4-5 KFT THIS MRNG WILL IMPACT THE TERMINALS EXCEPT FOR CHO BEFORE ERODING FROM S TO N THIS AFTN.NW WINDS AROUND 10 KT CONTINUES TNGT...WITH SLIGHTLY HIGHER WINDS AT DCA-BWI-MTN. NORTHWEST WINDS WILL GUST AROUND 20 TO 25 KNOTS THURSDAY ACROSS THE EASTERN TERMINALS. WINDS WILL BE LIGHTER ACROSS KMRB AND KCHO. HIGH PRESSURE OVER THE TERMINALS THURSDAY EVENING WILL SHIFT EAST OVERNIGHT. A SOUTHERLY FLOW WILL DEVELOP AHEAD OF A COLD FRONT DURING THIS TIME. THE COLD FRONT WILL PASS THROUGH THE TERMINALS FRIDAY WITH A FEW SHOWERS LIKELY. ANOTHER COLD FRONT WILL PASS THROUGH SATURDAY AFTERNOON AND EVENING AND IT WILL STALL OUT JUST TO THE SOUTH FOR SUNDAY. VFR CONDITONS ARE EXPECTED DURING THIS TIME.
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&& .MARINE...
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A STRONG PRESSURE GRADIENT OVER THE WATERS HAS PRODUCED WIDESPREAD 20-30 KT WIND GUSTS WITH LOCALLY HIGHER GUSTS TO 35 KT. GALE WARNING REMAINS IN EFFECT FOR ALL OF THE WATERS TDA. MIXING WILL DEEPEN EVEN FURTHER THIS AFTN BUT MODELS SHOW THE WIND FIELD AT THE TOP OF THIS MIXING LAYER WEAKENING A BIT. MAY BE ABLE TO CANCEL THE GALE WARNING A FEW HRS EARLY THIS AFTN WITH HIGH END SCA WINDS FAVORED. SCA CONTINUES TNGT. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS THURSDAY. WINDS WILL DIMINISH BY THURSDAY EVENING WITH HIGH PRESSURE OVERHEAD. HOWEVER...THE HIGH WILL MOVE OFF THE COAST THURSDAY NIGHT AND A COLD FRONT IS EXPECTED TO PASS THROUGH FRIDAY. ANOTHER COLD FRONT WILL LIKELY PASS THROUGH THE WATERS SATURDAY BEFORE STALLING OUT TO THE SOUTH FOR SUNDAY. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS FRIDAY THROUGH SUNDAY.
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&& .FIRE WEATHER...
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A RED FLAG WARNING HAS REPLACED THE FIRE WEATHER WATCH FOR MUCH OF THE MID ATLC REGION FROM 11 AM TO 8 PM TDA. NW WINDS OF 20-25 MPH WILL GUST FREQUENTLY BETWEEN 35 AND 40 MPH. MRNG UPDATE TO THE FCST KEEP MAX TEMPS AT OR EVEN A COUPLE OF DEGREES BELOW PREV FCST BUT DEWPOINTS WERE ALSO LOWERED THIS AFTN AS DRIER AIR MIXES DOWN TO THE SFC. PAST STUDIES HAVE SHOWN DEWPOINTS AT THE TOP OF THE BOUNDARY LAYER TO BE REPRESENTATIVE OF SFC DEWPOINTS DURING THE PEAK HEATINGS HRS IN SITUATIONS LIKE TDA. 12Z IAD RAOB SOUNDING SHOWS DEWPOINTS IN THE LOW TO MID 20S AT THE TOP OF THE BOUNDARY LAYER. THIS WILL RESULT IN RH VALUES BETWEEN 20 AND 30 PERCENT ACROSS THE MUCH OF THE AREA. FUEL MOISTURE OBS YDA WERE BETWEEN 5-8 PERCENT. ONLY LOCALIZED AREAS RECEIVED A COUPLE TENTHS OF AN INCH OF RAINFALL YESTERDAY...WHICH WAS NOT ENOUGH TO ALTER THE FUEL MOISTURE. WINDS SUBSIDE TOWARD SUNSET AND RH VALUES WILL INCREASE ABOVE CRITICAL THRESHOLDS. DRIER AIR WILL CAUSE EVEN LOWER RH VALUES THURSDAY...BUT WINDS WILL NOT BE AS STRONG. A FIRE WEATHER WATCH IS IN EFFECT FOR PORTIONS OF CENTRAL AND NORTHEASTERN MARYLAND WHERE THE WINDS WILL BE STRONGEST. A COLD FRONT WILL PASS THROUGH THE AREA FRIDAY...BRINGING A FEW SHOWERS BUT RAINFALL AMOUNTS WILL LIKELY AVERAGE OUT TO BE LIGHT.
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&& .TIDES/COASTAL FLOODING...
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STRONG NORTHWEST WINDS TODAY WILL CAUSE TIDAL BLOWOUT. THE NORTHWEST FLOW WILL CONTINUE THROUGH THURSDAY...BUT NOT AS STRONG. HOWEVER...TIDAL BLOWOUT CONDITIONS ARE POSSIBLE DURING THIS TIME AS WELL.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR DCZ001. FIRE WEATHER WATCH FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON FOR DCZ001. MD...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR MDZ003>007- 009>011-013-014-016>018-502. FIRE WEATHER WATCH FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON FOR MDZ004>007-009>011-013-014-018. VA...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR VAZ025>031- 036>040-042-050>057-501-502-504. FIRE WEATHER WATCH FROM THURSDAY MORNING THROUGH THURSDAY AFTERNOON FOR VAZ054. WV...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR WVZ050>053- 055-502-504-506. MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 PM EDT THURSDAY FOR ANZ530>543. GALE WARNING UNTIL 6 PM EDT THIS EVENING FOR ANZ530>543.
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&& $$ SYNOPSIS...BJL/JRK NEAR TERM...JRK/GMS SHORT TERM...BJL LONG TERM...BJL/GMS AVIATION...JRK/BJL MARINE...JRK/BJL FIRE WEATHER...JRK TIDES/COASTAL FLOODING...JRK/BJL

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