FXUS61 KLWX 161957 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 257 PM EST MON FEB 16 2009 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVER THE MID ATLANTIC TONIGHT INTO TUESDAY. THIS HIGH WILL MOVE OFF THE MID-ATLANTIC COAST LATE TUESDAY AS A STRONG STORM SYSTEM APPROACHES FROM THE WEST. LOW PRESSURE WILL PASS TO THE NORTHWEST OF THE AREA WEDNESDAY...WITH THE COLD FRONT PASSING THROUGH EARLY THURSDAY. AN UPPER LEVEL DISTURBANCE MAY BRING ADDITIONAL PRECIPITATION ON THURSDAY NIGHT. HIGH PRESSURE BUILDS OVER THE AREA FOR FRIDAY. ANOTHER LOW PRESSURE SYSTEM APPROACHES FROM THE NORTHWEST SATURDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... CURRENT ANALYSIS SHOWS AN UPPER-LEVEL DISTURBANCE MOVING OFF THE MID-ATLANTIC COAST WITH SURFACE HIGH BUILDING INTO THE REGION FROM THE OHIO VALLEY. LATEST SATILLITE IMAGERY SHOWS A STRONG CU FIELD THAT HAS DEVELOPED EARLY THIS AFTERNOON DUE TO INSTABILITY ASSOCIATED WITH THE UPPER-LEVEL DISTURBANCE. RADAR IMAGERY IS SHOWING ECHOES...BUT WITH LOW-LEVEL DRY AIR IN PLACE MOST PLACES REMAIN DRY. THE ONE EXCEPTION IS NEAR THE ALLEGHENY FRONT WHERE A LITTLE MORE INSTABILITY ALONG WITH AN UPSLOPE COMPONENT TO THE LOW-LEVEL FLOW HAVE TRIGGERED SNOW SHOWERS. A WINTER WEATHER ADVISORY IS IN EFFECT FOR THE POTOMAC HIGHLANDS THROUGH LATE THIS AFTERNOON. WILL LEAVE THE HEADLINE IN PLACE FOR THE REMAINDER OF THE AFTERNOON...BUT ACTIVITY SHOULD QUICKLY DISSIPATE THIS EVENING AS HIGH PRESSURE BUILDS CLOSER. ACROSS THE REST OF THE CWA...THE CU FIELD WILL QUICKLY DISSIPATE LATE THIS AFTERNOON INTO EARLY EVENING ALLOWING FOR MOSTLY CLEAR SKIES TONIGHT. MIN TEMPS WILL RANGE FROM NEAR 10 IN PORTIONS OF THE POTOMAC HIGHLANDS TO THE UPPER 20S IN WASHINGTON AND BALTIMORE. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... SURFACE HIGH OVER THE REGION TUESDAY WILL MOVE OFF THE MID-ATLANTIC COAST LATE IN THE DAY. MORE DRY AND SEASONABLE CONDITIONS ARE EXPECTED ALONG WITH SOME SUNSHINE. THE NEXT STORM SYSTEM WILL MOVE INTO THE PLAINS AND MID-WEST. HIGH CLOUDS WELL AHEAD OF THIS SYSTEM WILL MOVE INTO OUR AREA DURING THE DAY TUESDAY. THE LAYER SHOULD REMAIN THIN ENOUGH FOR MOSTLY TO PARTLY SUNNY SKIES. MAX TEMPS TUESDAY WILL RANGE FROM THE UPPER 30S IN THE POTOMAC HIGHLANDS TO THE MID 40S IN WASHINGTON DC. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... SFC RDG AXIS SLIDES OFFSHR TUE NGT...OPENING DOOR FOR ISENT LIFT IN RTN FLOW. ANTICIPATE CLDS TO INCR DUE TO UPGLIDE DURING THE EVNG. MEANWHILE...LOPRES WL BE MVG FM CNTRL PLAINS TO MIDWST...SOMEWHERE INVOF IL. THERE ARE SOME DIFFS IN THE DETAILS FM GDNC PROGS...BUT IN THE BIG PICTURE QUITE SIMLR. QPF FM THIS SYSTEM WL CREEP INTO WRN CNTYS PRIOR TO SUNRISE. WHILE WAA SHUD YIELD A MAINLY RA FCST GIVEN BNDRY LYR CONDS...THE TIMING OF PCPN ONSET /DIURNAL MIN/...AND THE LOW DEWPTS AT THAT TIME...MEAN THAT PCPN MAY START BRIEFLY AS SNW. ONLY PLACES WHERE PCPN WL BE MNTND TUE NGT WL BE FROSTBURG TO HARRISONBURG. WL SPREAD THAT /CHC SNW/ ACRS REST OF CWFA DURING THE MRNG...AS LLVL TKNS PROGS DEPICT A COOL SFC WEDGE IN THE NERN CWFA. TIME HGTS DEPICT ALMOST SIMULTANEOUS WAA SFC THRU 800 MB DURING THE MIDDAY...WHICH WL ENABLE ALL PCPN TO CHG OVR TO RA PRIOR TO PCPN RATES INCREASING. UPGLIDE AT ITS STRONGEST /50 KT LLJ/ DURING THE AFTN...JUST PRIOR TO THTE RDG AXIS NUDGING INTO CWFA WED NGT. WENT W/ CAT POPS /80 PCT/ WED AFTN...AND THEN SCALED BACK AS DEEPENING LOW AND H5 TROF RSLT IN DRY SLOT INTO CWFA AT NGT. DUE TO THE DRIER AIR WRAPPING ARND SYSTEM...PCPN SHUD END IN MOST LOCALES PRIOR TO H8 TEMPS/H10-8 TKNS DROPPING. ALLWD FOR CHC RASN NEAR END FOR NWRN HALF OF CWFA...BUT AT GREATLY REDUCED POPS. CAA WL RUSH INTO CWFA THU...AS H5 S/WV SHOOTS TWD CNTRL APPLCHNS FM GRTLKS...AND SFC LOW HEADS TWD CNDN MARITIMES AND DEEPENS. SETUP QUITE FVRBL FOR NMRS UPSLP SHSN...WHICH WL ONLY BE ENHANCED WHEN VORT CROSSES MTNS THU EVE. MNTN IN HWO MOST APPROPRIATE. ATTM...DONT HV POPS E OF THE HIGHLANDS DURING NW FLOW PHASE. BUT...WL NEED TO MONITOR THE VORT AXIS. IF ITS STRONG ENUF...IT CUD SUPPORT SCT SHSN E OF THE MTNS. OTRW...THU SHUD BE QUITE BRZY...WHICH WL SCOUR OUT CLDS...SPCLY E OF BLURDG. NW FLOW WL CONT ON FRI...W/ MORE OF THE SAME XPCTD FOR SENSIBLE WX-- UPSLP SHSN...PT-MOSUN E OF MTNS...AND BRZY EVERYWHERE. GNRL AGREEMENT FOR MOS TEMP FCSTS...AND ACCRDGLY HVNT STRAYED TOO FAR FM THE MACHINE NUMBERS. HV ALTERED THU MRNG MIN-T A BIT TO ACCOUNT FOR CFP NEAR DAWN...ENABLING PCPN TO REMAIN LIQ. THE THU MAXT WL BE THE TRICKIEST...AS IT/LL BE A BALANCE BTWN CAA AND COMPRESSIONAL WARMING FM DOWNSLP. ATTM...HV ACCEPTED GRIDDED/GFS MOS BLEND TIL DAY DRAWS NEARER. WND CHILLS MOST LIIKELY WL COME INTO PLAY THU-FRI. TEMPS WL CONT TO DROP SAT...AS WK LOW EMBEDDED W/IN MEAN LYR FLOW PASSES THRU CWFA. TIMING WL BE EVERYTHING FOR PTYPE...BUT UNLESS LOW PASSES DURING MID AFTN...AIR SHUD BE COLD ENUF FOR AT LEAST SOME SHSN. THERE/S ALSO SOME QSTN TO HOW MUCH OF THE LTMD MSTR THE MTNS WL BE ABLE TO WRING OUT BEFORE ENERGY JUMPS TO THE COAST AND AWAY FM AREA. CRRNT FCST WL KEEP MNTND PCPN W OF METRO CRRDR...AND PREDOMINANT PTYPE AS SHSN. LOW PASSAGE PROGGED FOR LT AFTN-ELY EVE...BUT THIS FAR OUT...ONE SHUD XPCT CHGS IN THE DETAILS AS THE EVENT DRAWS NEAR. UPSLP SHSN TO CONT INTO SUN...BUT BLDG HIPRES WL LWR HGT OF INVSN... DIMINISHING ACTVTY. OTRW...SUN-MON LOOKING DRY BUT COLD. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... HIGH PRESSURE WILL BRING VFR CONDITIONS TONIGHT AND TUESDAY. THE CU FIELD OVER THE TERMINALS THIS AFTERNOON WILL DISSIPATE BY THIS EVENING. SOME HIGH CLOUDS AHEAD OF THE NEXT SYSTEM WILL MOVE INTO THE AREA TUESDAY. NORTHWEST WIND GUSTS AROUND 20 KNOTS THIS AFTERNOON WILL DIMINISH THIS EVENING...AND LIGHT WINDS ARE EXPECTED TUESDAY. FLGT RESTRICTIONS XPCTD WED-WED NGT AS STORM SYSTEM TRACKS ACRS GRTLKS. PREDOMINANT PTYPE WL BE RA...BUT CANNOT RULE OUT A CHC AT SNW AT ONSET WED MRNG. DURING WED...RA WL OVRSPRD TERMINALS /OCNL AOB IFR/...W/ A 50 KT LLJ 3-4K FT YIELDING LLWS CONCERNS AS WELL. LOW TRACKS TO ERN GRTLKS BY THU MRNG. DRY AIR WRAPPING ARND SYSTEM SHUD END PCPN...AND FLGT RESTRICTIONS. BUT...STRONG W/NW WNDS SHUD PICK UP...SUSTAINED 15-20 KT...GUSTING TO 30 KT. GUSTY CONDS TO CONT INTO FRI...THO DIMINISHING SOMEWHAT. && .MARINE... WILL CONTINUE WITH THE SMALL CRAFT ADVISORY FOR WIND GUSTS UP TO 20 KNOTS INTO EARLY THIS EVENING ACROSS THE POTOMAC RIVER FROM KEY BRIDGE TO COBB ISLAND. WINDS WILL DIMINISH LATER THIS EVENING AS HIGH PRESSURE APPROACHES FROM THE WEST. HOWEVER...NORTHERLY WINDS ARE EXPECTED TO CHANNEL DOWN THE CHESAPEAKE BAY AND LOWER POTOMAC OVERNIGHT. WIND GUSTS UP TO 20 KNOTS ARE POSSIBLE DURING THIS TIME. HAVE EXTENDED THE SCA UNTIL 6AM FOR THIS PORTION OF THE WATERS. LOPRES WL TRACK FM CNTRL PLAINS TO CNTRL GRTLKS TUE NGT...AND TO ERN GRTLKS WHILE DEEPENING BY WED NGT. SLY WNDS WL PICK UP IN ADVC OF SYSTM WED AFTN...W/ CFP ELY THU MRNG. SCA PSBL THRUT THIS PD...AND CONTG INTO FRI DUE TO NW FLOW. CANT RULE OUT PSBLTY OF GLW THU NGT EITHER. HV KEPT WNDS AT 30 KT IN THE GRIDS FOR NOW. FOR THE WATERS...ALL PCPN FM THIS EVENT SHUD BE RA. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS AFTERNOON FOR VAZ021. WV...WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS AFTERNOON FOR WVZ054-501. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST TUESDAY FOR ANZ530>534-537. SMALL CRAFT ADVISORY UNTIL 8 PM EST THIS EVENING FOR ANZ535- 536. && $$ SYNOPSIS...BJL/HTS NEAR TERM...BJL SHORT TERM...BJL LONG TERM...HTS AVIATION...BJL/HTS MARINE...BJL/HTS