Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 150803 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 403 AM EDT TUE APR 15 2014 .SYNOPSIS...
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A STRONG COLD FRONT WILL MOVE THROUGH THE MID-ATLANTIC REGION FROM THE WEST TODAY. HIGH PRESSURE WILL MOVE NORTHEAST ACROSS THE NORTHERN MID-ATLANTIC WEDNESDAY...WITH COLD AIR DAMMING LINGERING UNTIL LOW PRESSURE AFFECTS THE REGION ON SATURDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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PRIMARY WX PLAYER FOR THE MID-ATLANTIC REGION IS A STRONG COLD FRONT THAT WILL MOVE THRU THE AREA TDA. THIS FRONT WAS LOCATED ON THE WRN SIDE OF THE APPALACHIANS AT 07Z AND IS MARKED BY A SHARP TEMP GRADIENT AND WIND SHIFT FROM S TO NW. STRONG SLY WINDS AND A DEEP POLEWARD MOISTURE TRANSPORT IN PRE-FRONTAL WARM SECTOR HAVE RESULTED IN TEMPS IN MILD AND MOIST CONDITIONS ACROSS THE CWA. UPSTREAM COVERAGE OF SHOWERS HAVE INCREASED OVER WRN NC/SWRN VA IN THE PAST FEW HRS AND WILL EXPAND INTO THE CWA FROM SW TO NE THRU THE MRNG. EXPECT WIDESPREAD SHOWERS ALONG AND WEST OF I-95 FOR MUCH OF THE MRNG. THERE IS VERY LITTLE INSTABILITY OVER THE AREA RIGHT NOW BUT INSTABILITY WILL INCREASE LATER THIS MRNG AND THIS AFTN AHEAD OF THE FRONT AS LLVL THETA-E RIDGE PROGRESSES NWD. DESPITE SBCAPE VALUES ONLY AROUND 500 J/KG AS SEEN ON THE LATEST NAM/RAP SOUNDINGS...STRONG WIND FIELD ALOFT WILL SUPPORT THE POTENTIAL FOR LOCALLY DAMAGING WINDS WITH ANY LOW-TOPPED CONVECTION THAT DEVELOPS. A LINEAR MODE OF CONVECTION WOULD BE FAVORED WITH THIS SETUP. IF CONVECTION DOES BECOME ORGANIZED...0-3 KM SHERB VALUES ABOVE 1 INDICATE THE POTENTIAL FOR DAMAGING WINDS ALONG AND EAST OF THE BLUE RIDGE LATE THIS MRNG AND ERY THIS AFTN. DAY 1 OUTLOOK FROM SPC HAS US IN A 5 PERCENT RISK OF DAMAGING WINDS. LOCALLY HEAVY RAINFALL WILL ALSO BE POSSIBLE TDA. LOCALLY HVY RAINFALL AMOUNTS AROUND 2 INCHES ARE POSSIBLE...AND COULD CAUSE SOME ISO FLOODING PROBLEMS IN POOR DRAINAGE AREAS. THE COLD FRONT WILL MOVE THRU THE MTS THIS MRNG AND EAST OF THE BLUE RIDGE THIS AFTN. A SHARP TEMP DROP WILL OCCUR BEHIND THE FRONT AS UNSEASONABLY COLD AIR MOVES IN. IT WILL ESSENTIALLY FEEL LIKE A CHANGE IN SEASONS FROM LATE SPRING AHEAD OF THE FRONT TO MORE LIKE WINTER IN LESS THAN 12 HOURS. A SIGNIFICANT POST-FRONTAL PRESSURE SURGE AND STRONG CAA WILL PRODUCE GUSTY WINDS.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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WEDNESDAY...HIGH PRESSURE BUILDS NORTHEAST ACROSS THE NRN MID-ATLANTIC...BECOMING A 1045 MB OR SO SFC HIGH OVER NEW ENGLAND WEDNESDAY NIGHT. MAX TEMPS AROUND 50F ARE 15 OR SO DEGREES BELOW NORMAL. SUNNY WITH PERHAPS SOME WISPY CIRRUS IN THE AFTERNOON OVERRUNNING A LOW AMPLITUDE RIDGE TO OUR WEST. STRONG NWLY GUSTS IN THE MORNING EASE THROUGH MIDDAY. PARTIAL DECOUPLING WEDNESDAY NIGHT WITH MIN TEMPS AROUND 30F INLAND...MID TO UPR 30S URBAN AND NEARSHORE. FREEZE WARNING LIKELY NEEDED...THOUGH MAYBE NOT FOR ALL ZONES EAST OF THE BLUE RIDGE LIKE TONIGHT.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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SFC PRESSURE RIDGE/COLD AIR DAMMING PERSISTS WEDNESDAY NIGHT INTO SATURDAY...WHEN THE NEXT DISTURBANCE DISLODGES THE ONSHORE FLOW. EXPECT BELOW NORMAL TEMPS TO CONTINUE WITH THE ONSHORE FLOW. AREAS EAST OF THE RIDGE AXIS BECOME SATURATED BY FRIDAY WITH DRIZZLE OR LIGHT RAIN POSSIBLE THEN THROUGH FRIDAY NIGHT. UNCERTAINTY ON SOUTHWARD EXTEND OF THE UPPER TROUGH MOVING WEST ACROSS THE NERN CONUS ON SATURDAY. CURRENTLY THE 00Z GFS IS MORE AMPLIFIED THAN THE 00Z ECMWF. THE COOL PATTERN CONTINUES THROUGH AT LEAST SUNDAY AS CANADIAN HIGH PRESSURE BUILDING IN BEHIND THE SATURDAY SYSTEM.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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MVFR CIGS AND VSBYS PREVAIL THROUGH THE DAY WITH INTERMITTENT IFR IN HEAVIER RAIN. ISO THUNDER THREAT TODAY. SLY FLOW GUSTS UP TO 30 KT AHEAD OF THE COLD FRONT APPROACHING FROM THE WEST. STRONG COLD FRONT CROSSES THE TERMINALS LATE THIS MORNING THROUGH THE EARLY AFTERNOON WITH A QUICK NWLY WIND SHIFT. GUSTS TO 35 KT LATE THIS AFTERNOON THROUGH TONIGHT ACROSS THE TERMINALS WITH A FEW SNOWFLAKES AT END OF PRECIP WEST OF BALT-WASH CORRIDOR. VFR WEDNESDAY AS HIGH PRESSURE BUILDS NORTHEAST ACROSS THE REGION WEDNESDAY. GUSTY NW WINDS EASE THROUGH MIDDAY. ONSHORE FLOW FROM COLD AIR DAMMING RIDGE THEN INTO SATURDAY WHEN THE NEXT LOW PASSES THE REGION. SUB-VFR CONDS POSSIBLY SPREAD FROM THE EAST FRIDAY AS THE ONSHORE FLOW SATURATES.
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&& .MARINE...
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SLY SCA LEVEL WINDS ACROSS THE WATERS. HOWEVER...AT 6AM THE SCA UPGRADES TO A GALE WARNING TO ACCOUNT FOR POSSIBLE SLY GALES IN RAIN LATER THIS MORNING...AS WELL AN EXPECTED 4PM ONSET OF NWLY GALES BEHIND THE COLD FRONT. GALE WARNING THROUGH TONIGHT WITH 40 KT POSSIBLE OVER ALL OF THE WATERS. GALES POSSIBLE FOR LOWER SRN MD WATERS EARLY WEDNESDAY MORNING...BUT BUT HAD CONFIDENCE TO SIMPLY ISSUE AN SCA FOR ALL WATERS UNTIL 3PM AND MD BAY WATERS UNTIL 6PM WEDNESDAY AS HIGH PRESSURE BUILDS NORTHEAST ACROSS THE REGION. ONSHORE FLOW THEN OVER THE REGION INTO SATURDAY. ELY FLOW 15 TO 20 KT/SCA LIKELY FOR THURSDAY.
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&& .TIDES/COASTAL FLOODING...
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NWLY GALES TUESDAY NIGHT AND STRONG SCA WINDS INTO WEDNESDAY AFTERNOON WILL CAUSE BLOWOUT TIDE CONDITIONS FOR THE LOW TIDES ON WEDNESDAY. OF PARTICULAR CONCERN IS THE MIDDAY/AFTERNOON LOW TIDE CYCLE WHERE WATER LEVELS LOOK TO DROP TO AROUND 2 FEET BELOW MLLW.
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&& .CLIMATE...
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RECORD DAILY HIGH MINIMUM TEMPERATURES WERE SET FOR DCA AND IAD... AND TIED FOR BWI. BELOW IS A TABLE OF RECORDS FOR APRIL 14 AND LOW TEMPERATURES OBSERVED. SITE...PREV RECORD......LOW... DCA....63F IN 1896......65F... BWI....62F IN 1896......62F... IAD....58F IN 1972......63F...
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...FREEZE WARNING FROM 3 AM TO 9 AM EDT WEDNESDAY FOR DCZ001. MD...FREEZE WARNING FROM 3 AM TO 9 AM EDT WEDNESDAY FOR MDZ011-013- 014-016>018. FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT WEDNESDAY FOR MDZ004>007-009-010. VA...FREEZE WARNING FROM 3 AM TO 9 AM EDT WEDNESDAY FOR VAZ052>057. FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT WEDNESDAY FOR VAZ036>040-042-050-051-501-502. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ530>543. SMALL CRAFT ADVISORY FROM 6 AM TO 6 PM EDT WEDNESDAY FOR ANZ531>534-537-539>541-543. GALE WARNING FROM 6 PM THIS EVENING TO 6 AM EDT WEDNESDAY FOR ANZ530>543. SMALL CRAFT ADVISORY FROM 6 AM TO 2 PM EDT WEDNESDAY FOR ANZ530-535-536-538-542.
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&& $$ SYNOPSIS...BAJ/JRK NEAR TERM...JRK SHORT TERM...BAJ LONG TERM...BAJ AVIATION...BAJ MARINE...BAJ TIDES/COASTAL FLOODING...BAJ CLIMATE...BAJ

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