FXUS64 KLIX 221312
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
712 AM CST TUE DEC 22 2009

.UPDATE...
.SOUNDING DISCUSSION...

OVERALL THE ATMOSPHERE REMAINS DRY WITH A LARGE AREA OF DRY AIR FROM
900 MB TO 475 MB. A BIT OF MOISTURE IS PRESENT AT THE SURFACE AND
NEAR 3700 FEET WHERE A FEW STRATOCUMULUS CLOUDS ARE
PRESENT...PRECIPITABLE WATER VALUE IS 0.45 INCHES. AN INVERSION IS
PRESENT NEAR 600 FEET AND A SECONDARY INVERSION NEAR 5600 FEET.
WINDS ARE OUT OF THE SOUTH AND SOUTHWEST IN THE LOWER
LEVELS...WEST IN THE MID LEVELS AND NORTHWEST ALOFT.

&&

.PREV DISCUSSION... /ISSUED 432 AM CST TUE DEC 22 2009/ 

SHORT TERM...
SIMILAR CONDITIONS ACROSS THE AREA FROM YESTERDAY BUT WITH A FEW 
CHANGES. GENERALLY...TEMPS AND DEWPOINTS ARE ABOUT 5 DEGREES WARMER. 
DEWPOINT SPREADS ARE A LITTLE HIGHER WHICH HAS RESULTED IN LESS 
WIDESPREAD FOG DEVELOPMENT SO HAVE TRIMMED OUT MUCH OF AREAS OF 
DENSE FOG TO PATCHY DENSE. LOCATIONS ALONG THE PEARL RIVER IN ST. 
TAMMANY PARISH AND PEARL RIVER/HANCOCK COUNTIES AS WELL AS HARRISON 
ARE THE MOST SUSCEPTIBLE TO MORE WIDESPREAD DENSE FOG. NO PLANS ATTM 
TO ISSUE DENSE FOG ADVISORY BUT WILL CONTINUE TO MONITOR. 

SURFACE HIGH NOW TO THE EAST OF THE AREA WILL PROMOTE INCREASE 
MOISTURE WITH SERLY WINDS ON THE INCREASE TODAY. TEMPERATURES WILL 
CONTINUE TO MODERATE WITH INCREASING THICKNESSES. STAYED VERY CLOSE 
TO MAV FCST HIGHS DUE TO ITS GOOD PERFORMANCE THE LAST FEW DAYS. 
SHOULD SEE HIGHS FROM THE MID TO UPPER 60S WITH A FEW 70S POSSIBLE. 
CLOUDS WILL BE ON THE INCREASE FROM THE WEST TODAY BUT SHOULD MOSTLY 
BE IN THE FORM OF CIRRUS. THE INTRODUCTION OF SHOWERS INTO THE 
FORECAST BEGINS TONIGHT WITH THE FOCUS ON EXTREME NWRN ZONES. POPS 
AROUND 30 MAY BE A LITTLE ON THE GENEROUS SIDE. CONTINUED INCREASING 
CLOUDS AND MOISTURE WILL RESULT IN SUBSTANTIALLY WARMER LOWS TONIGHT 
WITH TEMPS ONLY DROPPING INTO THE MID 50S.  
 
LONG TERM...
UPPER TROUGH WILL BE DIGGING SEWD ACROSS THE WESTERN HALF OF THE 
COUNTRY TODAY AND WEDNESDAY. MODELS HAVE BACKED OFF SOME ON POPS 
WEDNESDAY. NO ARGUMENTS HERE AND GOES BETTER WITH UNDERCUTTING 
GUIDANCE YESTERDAY FOR THAT PERIODS POPS. SH/TS POTENTIAL WILL 
PROGRESSIVELY INCREASE WED NIGHT OUT AHEAD OF APPROACHING COLD 
FRONT. MODEL SOUNDINGS SUGGEST PW/S COMING UP TO AROUND 1.5 INCHES 
BY MIDNIGHT. THINKING IS THAT A SQUALL LINE WILL DEVELOP ALONG THE 
FRONT AND MOVE THROUGH THE CWA THURSDAY AFTN AND INTO THE EARLY 
EVENING HRS. THIS COINCIDES WITH THE ECMWF/GFS SPEED AS OPPOSED TO 
THE SLIGHTLY SLOWER NAM12. INSTABILITY WILL BE FAIRLY MARGINAL BUT 
SHOULD HAVE ENOUGH FORCING ALONG THE BOUNDARY FOR A SVR WX THREAT. 
MAIN THREAT WILL BE DAMAGING WINDS WITH ISOLATED TORNADOES. 

ONCE THE FRONT CLEARS THE AREA THURSDAY NIGHT...HIGH PRESSURE WILL 
BUILD IN FROM THE NW AND PERSIST THROUGH EARLY NEXT WEEK. MEX TEMPS 
LOOK TO BE ON THE WARM SIDE FOR SUCH PERSISTENT NWRLY COLD AIR 
ADVECTION...SO HAVE UNDERCUT GUIDANCE. MODEL SOLUTIONS DIFFER 
TOWARDS THE END OF THE PERIOD. WHILE ECMWF AND GFS BOTH SHOW AN AREA 
OF LOW PRESSURE DEVELOPING AND TRACKING ALONG THE GULF COAST...ECMWF 
HAS A MUCH STRONGER INVERTED UPPER TROUGH AND SFC LOW TRACKING 
DIRECTLY ACROSS CWA WHILE THE GFS KEEPS THE SFC LOW FARTHER SOUTH IN 
THE GULF WATERS AND THUS MUCH LESS RAIN ACROSS THE CWA. 

MEFFER

AVIATION...
FOG APPEARS TO BE HELD AT BAY THUS FAR TONIGHT AS DEWPOINT SPREADS 
ARE MAINTAINING 2+C ACROSS MUCH OF THE AREA. SOME GROUND FOG NOTED 
AT KBIX AND KPQL AROUND 2SM. KMCB BOUNCING FROM 2SM TO 4SM. SUBTLE 
BUT STEADY WARM AIR ADVECTION MAY OFFSET SURFACE INVERSION ENOUGH TO 
PRECLUDE MUCH FOG IMPACT THIS MORNING BUT TEMPO 1-2 HR OF 1-2SM BR 
POSSIBLE BEFORE 1430Z. MID LEVEL CLOUDS SHOULD STEADILY INVADE FROM 
THE SOUTHWEST AS NEXT STORM SYSTEM DEVELOPS AND MATURES IN THE 
PLAINS STATES NEXT 24 HOURS. VFR CONDITIONS SHOULD PREVAIL THROUGH 
18Z WEDNESDAY. 24/RR

MARINE...
WINDOW OF LIGHT WINDS AND LOW SEAS WILL SLOWLY CLOSE AS RETURN FLOW 
GETS UNDERWAY LATER TODAY AND ESPECIALLY TONIGHT. MODERATE RETURN 
FLOW NOTED IN THE WEST GULF THIS MORNING WILL SPREAD EAST IN TIME. 
STRONG COLD FRONT WITH PRE-FRONTAL SQUALL LINE STILL EXPECTED TO 
MOVE THROUGH LA AND MS COASTAL WATERS THURSDAY WITH COLD HIGH 
PRESSURE BUILDING IN ITS WAKE THROUGH FRIDAY. SMALL CRAFT ADVISORY 
CONDITIONS SHOULD ONSET TONIGHT WITH THE ACTUAL ADVISORY PROBABLY 
POSTED WITH AFTERNOON COASTAL FORECAST ISSUANCE. 24/RR

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  66  53  66  58 /   0  20  30  60 
BTR  69  56  72  59 /  10  30  30  60 
MSY  68  56  74  61 /   0  20  20  50 
GPT  65  53  67  59 /   0  10  20  40 

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
GM...NONE.
MS...NONE.
GM...NONE.
&&

$$