Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 151419 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1019 AM EDT TUE APR 15 2014 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 7 PM THIS EVENING/...
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STRONG COLD FRONT PASSING OVER OUR WESTERN COUNTIES IN THE MOUNTAINS AT 10AM IS CAUSING A FEW THREATS TO DEAL WITH... FIRST IS ENOUGH WIND SHEAR IN THE LOW LEVELS TO CAUSE SOME ROTATING SEGMENTS IN LOWER S MD DURING THE MID TO LATE MORNING. THERE IS A ISOLATED THREAT OF DAMAGING WINDS WITH THESE AS THEY MOVE EAST. RADAR TEAM IS MONITORING. THING LIMITING THIS IS THE LOW LEVEL STABILITY IN THE BOUNDARY LAYER AND THE VERY LIMITED AMOUNT OF INSTAB OVER THAT. SECOND IS ISOLATED FLOODING THREAT. THE ENHANCED AREAS ON RADAR OVER THE ADJACENT BAY COUNTIES AND BALTIMORE AT 10AM ARE PRODUCING A HALF INCH TO INCH OF RAIN IN ABOUT AN HOUR AS THEY PASS BY. AT THIS TIME BASED ON 1 HR AND 3 HR FLASH FLOOD GUIDANCE...THINK GENERALLY THE RAIN WILL BE ABSORBED BY THE SPRING GROUND AND EMERGING VEGETATION. HOWEVER SOME ISOLATED AREAS OF LOCALIZED FLOODING ARE POSSIBLE LATE THIS MORNING IN THESE COUNTIES AND BALTIMORE. THIRD IS COLD AIR COMING IN WITH PRECIP AROUND. LATEST MESO MODEL GUIDANCE HAS SNOW CHANGEOVER IN THE POTOMAC HIGHLANDS IN OUR HIGHEST SPOTS OUT WEST CHANGING OVER IN THE EARLY AFTERNOON. OTHER THREAT OF CHANGEOVER AND SOME LIGHT ACCUMS ON THE BLUE RIDGE AND N CENTRAL MD HIGHLANDS ISNT EXPECTED UNTIL EVENING JUST BEFORE THE PRECIP KICKS OUT. AT THIS POINT NOT EXPECTING SNOWFLAKES OVER THE METRO AREA...BUT SOME WET NON ACCUM FLAKES POSSIBLE AT THE END. EXPECT THE MORNING LINE OF HEAVY PRECIP OVER THE BAY COUNTIES TO KICK EAST DURING THE LATE MORNING. THAT SHOULD LEAVE A FEW HOURS OF SCT SHOWERS BEFORE ANOTHER SHIELD OF PRECIP DEVELOPS OVER THE AREA EARLY THIS AFTERNOON WHICH WILL LAST THE REST OF THE DAY.
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&& .SHORT TERM /7 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
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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. 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/... 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 /14Z TUESDAY THROUGH SATURDAY/... 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. && .MARINE... 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. && .TIDES/COASTAL FLOODING... 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. && .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 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...CAS SHORT TERM...BAJ LONG TERM...BAJ AVIATION...BAJ/JRK/CAS MARINE...BAJ/JRK/CAS TIDES/COASTAL FLOODING... CLIMATE...

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