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Area Forecast Discussion

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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/...
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.

&&

.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/...
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.

&&

.MARINE...
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.

&&

.FIRE WEATHER...
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.

&&

.TIDES/COASTAL FLOODING...
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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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.

&&

$$
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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