Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 150923 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 523 AM EDT TUE APR 15 2014 .SYNOPSIS...
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A STRONG COLD FRONT WILL MOVE THROUGH THE MID-ATLANTIC REGION TODAY. ARCTIC HIGH PRESSURE BUILDS INTO THE REGION TONIGHT AND WEDNESDAY. THE CENTER OF THE HIGH SHIFTS NORTHEAST INTO NEW ENGLAND BUT CONTINUES TO RIDGE SOUTHWARD INTO THE MID-ATLANTIC REGION LATE IN THE WEEK.
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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 MILD AND MOIST CONDITIONS ACROSS THE CWA WITH TEMPS IN THE MID TO UPPER 60S AND DEWPOINTS NEAR 60S BEFORE SUNRISE. 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 DAYBREAK. EXPECT WIDESPREAD SHOWERS ALONG AND WEST OF I-95 FOR MUCH OF THE MRNG. ENVIRONMENT FAIRLY STABLE ATTM BUT MODEST INSTABILITY WILL DEVELOP LATER THIS MRNG AND AFTN AHEAD OF THE FRONT AS LLVL THETA-E RIDGE PROGRESSES NWD INTO THE MID-ATLANTIC REGION. STRONG WIND FIELD ALOFT WILL SUPPORT THE POTENTIAL FOR LOW-TOPPED CONVECTION THAT COULD ORGANIZE INTO A LINE. 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. WITH DENSE CLOUD COVER THIS MRNG...THE LIMITING INGREDIENT FOR SEVERE WEATHER WILL BE INSTABILITY. FCST SBCAPE VALUES ONLY AROUND 500 J/KG AS SEEN ON THE LATEST NAM/RAP SOUNDINGS. THE LATER TIMING OF THE FROPA COULD ALLOW FOR A BIT MORE INSTABILITY TO DEVELOP IN SRN MD THIS AFTN. RAINFALL AMOUNTS OF 1-2 INCHES ARE EXPECTED ALONG AND EAST OF THE BLUE RIDGE. LOCALLY HIGHER AMOUNTS COULD CAUSE ISO FLOODING PROBLEMS MAINLY 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 SPRING AHEAD OF THE FRONT TO MORE LIKE WINTER) IN LESS THAN 12 HOURS. THERMAL PROFILES COOL FAST ENOUGH TO SUPPORT RAIN CHANGING TO A BRIEF PERIOD OF SNOW FROM WEST TO EAST LATE THIS AFTN INTO THIS EVE AT HIGHER ELEVATIONS AS FAR EAST AS THE BLUE RIDGE AND EVEN EXTREME NRN CARROLL AND FREDERICK COUNTIES BEFORE ENDING. A WARM GROUND IN MID APRIL WILL MAKE IT CHALLENGING FOR SNOW TO ACCUMULATE BUT ITS CERTAINLY POSSIBLE FOR LIGHT ACCUMULATIONS ON GRASSY SURFACES AT ELEVATIONS ABOVE 1000 FT. USPLOPE LIFT WILL SUPPORT SNOW TO CONTINUE LONGER ALONG THE WRN SLOPES OF THE ALLEGHENY FRONT. SNOWFALL AMOUNTS AROUND AN INCH ARE POSSIBLE OUT THERE. A SIGNIFICANT PRESSURE SURGE TO ACCOMPANY THE STRONG CAA WILL PRODUCE GUSTY WINDS BEHIND THE FRONT. CONSIDERED A WIND ADVISORY... PARTICULARLY FOR THE HIGHER ELEVATION RIDGES BUT WINDS AT THE TOP OF THE MIXING LAYER ONLY MARGINALLY SUPPORTIVE OF ADVISORY LVL WIND GUSTS. THE STRONGEST WINDS WILL OCCUR IN THE ERY EVE...ALLOWING THE DAY SHIFT TO LOOK THRU THE LATEST TRENDS IN OBS AND NEAR-TERM GUIDANCE. MIN TEMPS TNGT AOB FREEZING FOR THE ENTIRE CWA EXCEPT IN THE CITIES AND ALONG THE WRN SHORE OF THE CHSPK BAY. FREEZE WARNINGS ISSUED FOR COUNTIES EAST OF THE BLUE RIDGE...WHERE THE GROWING SEASON HAS ALREADY BEGUN.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... 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. && .LONG TERM /THURSDAY THROUGH MONDAY/... 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. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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MVFR CIGS AND VSBYS PREVAIL THROUGH THE DAY WITH INTERMITTENT IFR IN HEAVIER RAIN. ISO THUNDER THREAT TDA EAST OF MRB AHEAD OF THE FRONT. SLY FLOW GUSTS UP TO 30 KT AHEAD OF THE COLD FRONT THAT IS 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 POSSIBLE AT THE 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 HEAVIER SHOWERS LATER THIS MORNING...AS WELL AN EXPECTED LATE AFTN ONSET OF NWLY GALES BEHIND THE COLD FRONT. GALE WARNING THROUGH TONIGHT WITH 30-40 KT GUSTS EXPECTED ACROSS 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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POSITIVE TIDAL ANOMALIES REMAIN STEADY ERY THIS MRNG AROUND 3/4 FT ALONG THE WRN SHORE OF THE CHSPK BAY AND BELOW 1/2 FT IN THE TIDAL POTOMAC. NO COASTAL FLOODING EXPECTED. 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... 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... && .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 AM EDT EARLY THIS MORNING FOR ANZ530>543. SMALL CRAFT ADVISORY FROM 6 AM TO 6 PM EDT WEDNESDAY FOR ANZ531>534-537-539>541-543. GALE WARNING UNTIL 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/JRK MARINE...BAJ/JRK TIDES/COASTAL FLOODING...JRK/BAJ CLIMATE...BAJ

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