572 FXUS61 KLWX 190046 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 846 PM EDT MON MAR 18 2013 .SYNOPSIS... A COLD FRONT WILL APPROACH THE AREA TONIGHT BEFORE PASSING THROUGH EARLY TUESDAY. HIGH PRESSURE WILL BUILD OVERHEAD TUESDAY NIGHT INTO WEDNESDAY BEFORE ANOTHER COLD FRONT MOVES THROUGH WEDNESDAY NIGHT. HIGH PRESSURE WILL RETURN FOR LATE IN THE WEEK. && .NEAR TERM /UNTIL 7 AM TUESDAY MORNING/... LTST SFC ANALY DEPICTS LOPRES OVER THE GRTLKS...W/ ATTENDENT CDFNT ERN OH/ERN KY/ERN TN. A RDG OF HIPRES CAN BE FOUND JUST E OF THE APLCHNS...W/ 2NDRY LOPRES DVLPMNT INVOF CAPE HATTERAS/CAPE HENRY. PRACTICALLY ALL OF THE PCPN CAN BE FOUND STREAMING NWD AHD OF THE CDFNT...COINCIDENT W/ BEST WAA. THUS...THE WARM NOSE IS OVERRIDING COOL SFC TEMPS...STEEPENING AN INVSN. 00Z LWX RAOB MIMICS WHAT HAS BEEN OBSVD FM ACARS DATA...W/ TEMPS DROPPING BELOW FRZG ARND 1200 FT ELEV...THEN A WARM NOSE NOTED BTWN 900-725 MB. THAT MAKES PTYPE FCSTG QUITE A CHALLENGE...BUT CONFIRMS THAT THE I-95 CRRDR HAS REMAINED PRIMARILY JUST RA. /ANY HEAVIER BURSTS OF PCPN MAY SUPPORT POCKETS OF SNW OR PL TO MAKE IT DOWN./ WHILE THE BACK EDGE OF RDR ECHOES SEEMINGLY WAS WORKING ACRS WRN CWFA TWD SUNSET...DP LYR MSTR AND ISENT LIFT HAS SUPPORTED SOME RDVLPMNT TO THE PCPN. SINCE TEMPS ACRS THE RDGS STILL SUPPORT FZRA...WL BE HOLDING ONTO WINTER WX ADVY AS IS FOR WRN HALF OF CWFA-- EVEN THO THIS IS A HIER ELEV EVENT. THE CHARACTER OF RDR RETURNS SUGGEST THAT ICE ACCRETION WONT BE SGFNT...BUT TRACE ICING /WHICH IS THE CRITERION/ SEEMS REASONABLE. ENDING TIME REMAINS 2AM... WHICH IS WHEN THE APPCHG CDFNT SHUD SHOVE THE PLUME OF MSTR EWD. TEMPS HVNT EXHIBITED MUCH TEMP CHG TDA...NOR IS IT XPCTD TNGT. MAY GET A BRIEF SPIKE INVOF FNT AS THE WARMER AIR IS MIXED DOWN PRIOR TO FROPA. && .SHORT TERM /7 AM TUESDAY MORNING THROUGH THURSDAY/... SURFACE HIGH PRESSURE WILL BUILD BRIEFLY INTO THE REGION BEFORE ANOTHER COLD FRONT MOVES THROUGH WEDNESDAY NIGHT. UPSLOPE SNOW SHOWERS WILL REDEVELOP ALONG THE EASTERN WV MOUNTAIN AREAS WEDNESDAY NIGHT INTO THURSDAY MORNING. NAM20 HAS 40-50 KT OF WIND ALONG THE MOUNTAINS AND GFS SPREADS 925 MB TEMPERATURES -5 TO -8C BEHIND THE FRONT. THE GFS IS A BIT SLOWER WITH THE TIMING OF THE FRONT. THE FORECAST WILL HAVE SOME LOOKS AT THE SUN DURING THE DAY WEDNESDAY BEFORE CLOUDS INCREASE BY AFTERNOON. WE NUDGED TEMPERATURES DOWN A BIT PER ADJMAV AND ECMWF GUIDANCE...BELOW NORMAL TEMPS LIKELY TO CONTINUE WITH HIGHS ONLY IN THE UPPER 40/S TO NEAR 50. WITH INCREASING WINDS IT WILL FEEL QUITE BRISK IN THE MOUNTAINS...WIND CHILLS IN THE 20S ARE POSSIBLE. THURSDAY WILL START OUT CLOUDY AND THEN SOME CLEARING IS LIKELY LATER IN THE DAY. ONCE AGAIN WE'LL SEE BRISK NW WINDS AND TEMPERATURES THAT REMAIN IN THE 40S. ANY SNOW ACCUMULATION IN THE MOUNTAINS IS EXPECTED TO BE LIGHT. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... THE BLOCKING RIDGE OVER GREENLAND BREAKS DOWN AND IS REPLACED BY A TROF AS A HIGH AMPLITUDE RIDGE DEVELOPS ALONG THE WEST COAST DURING THIS PERIOD. A BROAD TROF STRETCHES FROM THE INTERIOR NORTHWEST STATES TO THE GREAT LAKES. THE UPPER LOW OVER NEW ENGLAND FILLS AND LIFTS EAST AS AN UPPER RIDGE PUSHES INTO THE OHIO VALLEY FRIDAY. FRIDAY MORNING MAY START OUT QUITE COLD AND ONLY WARM INTO THE 40/S IN THE METRO AREAS AGAIN. IT LOOKS LIKE IT WILL BE SUNNY AND PERHAPS THE MARCH SUNSHINE WILL WARM THINGS UP A FEW DEGREES MORE. AS THE RIDGE SHIFTS OVERHEAD HI CLOUDS INCREASE SATURDAY / SATURDAY NIGHT. THE GFS BRINGS SOME OVERRUNNING SHOWERS INTO THE WESTERN AREAS SATURDAY NIGHT. IT ALSO SHOWS A 110KT JET OVER THE ROCKIES LATE SATURDAY WHICH CARVES OUT AN UPPER LOW WITH A NEGATIVE TILT OVER THE SE STATES. A 996MB SURFACE LOW BOMBS OUT OVER TENNESSEE EARLY SUNDAY. THE ECMWF HAS THIS MUCH FARTHER SOUTH HOWEVER. A DIFFLUENT FLOW OVER THE MID ATLANTIC COULD LEAD TO A CHANCE OF SHOWERS SUNDAY IF THE GFS IS RIGHT. THERE IS A HIGH DEGREE OF UNCERTAINTY IN THE FORECAST OUT TOWARD MONDAY AS SOME MODELS SHOW GOOD PHASING OF ENERGY FROM A CLIPPER TYPE SYSTEM WITH A SOUTHERN BRANCH SYSTEM...BRINGING ANOTHER PERIOD OF UNSETTLED WEATHER. WE WILL CONTINUE TO MONITOR THIS. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... CIGS/VSBYS MAINLY AOB IFR. WARM AIR WL BE OVERRIDING COOL SFC CONDS TNGT...A PTTN WHICH SUPPORTS LOW FLGT CATEGORIES...SO ANY FORAY TO MVFR SHUD BE BRIEF. A COLD FRONT WILL CROSS THE TERMINALS PREDAWN AND MOVE OFFSHORE EARLY TUESDAY MORNING. WNDS WL VEER WLY AND CIGS/VSBYS WILL IMPROVE BEHIND THE FRONT. GUSTY WEST-NORTHWEST WINDS ARE EXPECTED TUESDAY AFTERNOON. WIND GUSTS AROUND 25 KNOTS ARE EXPECTED. WEDNESDAY BEGINS VFR UNDER SURFACE HI PRESSURE. A COLD FRONT WILL MOVE THROUGH WEDNESDAY NIGHT AND EARLY THURSDAY WITH MVFR CIGS OVC030 LATE IN THE DAY WEDNESDAY TO EARLY THURSDAY AT THE IAD...BWI AND DCA TERMINALS. IFR RASN LIKELY ALONG THE WV MTNS DURING THIS TIME. MVFR TO VFR REDEVELOPS THURSDAY DURING THE DAY AS UPSLOPE SHOWERS CONTINUE ALONG THE MTNS. VFR LIKELY FRIDAY AS SURFACE HI PRESSURE RETURNS. && .MARINE... A WEDGE OF COOL STBL AIR RESIDES E OF THE APLCHNS THIS EVNG...AND THUS OVER THE WATERS. WNDS MAINLY E OR NE. WINDS NO HIER THAN 10-15 KT...AND ALL SCA/S HV BEEN DROPPED. A COLD FRONT WILL PASS THROUGH THE WATERS EARLY TUESDAY. WEST- NORTHWEST WINDS WILL INCREASE BEHIND THE FRONT LATER TUESDAY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS. THE STRONGEST WINDS ARE EXPECTED IN THE AFTERNOON. BREEZY W-NW WINDS DECREASE AND SHIFT TO THE SOUTHWEST DURING THE DAY WEDNESDAY UNDER HIGH PRESSURE. A COLD FRONT WILL PASS OVER THE WATERS LATE WEDNESDAY NIGHT INTO EARLY THURSDAY WITH LITTLE MOISTURE. HOWEVER THERE WILL BE CLOUDS AND GUSTY W-NW WINDS ONCE AGAIN THURSDAY. HIGH PRESSURE BUILDS IN FRIDAY WITH LESS WIND. && .TIDES/COASTAL FLOODING... TIDAL DEPARTURES REMAIN AOB 1 FT ABOVE NORMAL THIS EVNG. DO NOT EXPECT MUCH CHG THRU THE NIGHTTIME TIDE CYCLE. THEREFORE BELIEVE THAT THERE WL BE NO PROBLEMS TNGT. WNDS WL TURN NWLY TUE MRNG...WHICH SHUD PUSH THE EXCESS WATER OUT OF THE BAY/TIDAL PTMC. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...WINTER WEATHER ADVISORY UNTIL 2 AM EDT TUESDAY FOR MDZ003-004- 501-502. VA...WINTER WEATHER ADVISORY UNTIL 2 AM EDT TUESDAY FOR VAZ025>031- 036>040-042-501-503-504. WV...WINTER WEATHER ADVISORY UNTIL 2 AM EDT TUESDAY FOR WVZ050>053- 055-501>506. MARINE...SMALL CRAFT ADVISORY FROM 10 AM TO 8 PM EDT TUESDAY FOR ANZ530>543. && $$ SYNOPSIS... NEAR TERM...HTS SHORT TERM...SDG LONG TERM...SDG AVIATION...HTS/BJL/SDG MARINE...HTS/BJL/SDG TIDES/COASTAL FLOODING...HTS