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