873 
FXUS64 KLIX 210544
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1144 PM CST FRI NOV 20 2009

.AVIATION...
MAINLY JUST SPRINKLES FALLING FROM MID LEVELS CLOUDS WERE
OCCASIONALLY BEING OBSERVED AT THE TAF SITES AS A LAYER OF DRY AIR
IN THE LOWER LEVELS PREVAILED ACROSS THE FORECAST AREA LATE THIS
EVENING. AS THE COLUMN BECOMES SATURATED OVERNIGHT...MORE IN THE
WAY OF LIGHT RAIN WILL BE OBSERVED TOWARD MORNING. THIS FIRST
BATCH OF LIGHT RAIN WAS RESULTING FROM A LEAD SHORT WAVE MOVING
ACROSS THE REGION. MORE SUBSTANTIAL RAIN WAS OCCURRING TO THE
SOUTHWEST OF LAKE CHARLES AND THIS RAIN WILL GRADUALLY MAKE ITS
WAY INTO THE FORECAST AREA LATE TONIGHT AND SATURDAY MORNING.
OCCASIONAL LIGHT RAIN CAN BE EXPECTED AT THE TERMINAL SITES DURING
THE DAY SATURDAY. THE LATEST MODEL GUIDANCE APPEARS TO BE SOMEWHAT
SLOWER IN MOVING THE RAIN OUT OF THE AREA...THEREFORE RAIN MAY
LINGER THROUGH SATURDAY EVENING AT MOST LOCATIONS. VFR CEILINGS TONIGHT
WILL LOWER TO MVFR CEILINGS DURING THE MID AND LATE MORNING HOURS
SATURDAY...AND THEN INTO THE IFR RANGE SATURDAY EVENING. LIGHT
RAIN AND LIGHT FOG WILL RESULT IN MVFR VISIBILITIES DURING MUCH OF
THE DAY SATURDAY. 11

&&

.PREV DISCUSSION... /ISSUED 911 PM CST FRI NOV 20 2009/ 

UPDATE...
THERE IS FINALLY SOME WEATHER TO TALK ABOUT THIS EVENING. A
SERIES OF WELL DEFINED UPPER LEVEL DISTURBANCES ARE MOVING EAST
ACROSS THE WESTERN GULF COAST REGION. THE LEAD SHORTWAVE IS
NEAR THE WESTERN BORDER OF THE FORECAST AREA AND IS PRECEDED BY
PATCHY LIGHT RAIN...MOSTLY FALLING AS SPRINKLES WITH ONLY TRACE
RAINFALL AMOUNTS REPORTED THUS FAR DUE TO THE VERY DRY AIR BELOW
700 MB. THERE IS LIKELY SOME MEASURABLE LIGHT RAIN REACHING THE
GROUND OVER THE COASTAL WATERS FROM SOUTHWEST PASS TO THE LOWER
ATCHAFALAYA RIVER. DEEPER CONVECTION WITH LIGHTNING IS OCCURRING
FARTHER OFFSHORE NEAR THE MIDDLE BUOY /42001/.

THERE IS A BREAK BEHIND THIS FIRST DISTURBANCE WITH NO RAIN
CURRENTLY BEING REPORTED ACROSS MUCH OF SOUTHWEST LOUISIANA.
RADAR SHOWS ONLY ISOLATED SHOWER ACTIVITY OFF THE COAST OF
SOUTHWEST LOUISIANA.

FARTHER WEST...THE MAIN...STRONGER SHORTWAVE TROUGH AND DEVELOPING
UPPER LOW IS OVER CENTRAL TEXAS AND PRECEDED BY ANOTHER
DISTURBANCE AND THE MAIN SURFACE LOW NEAR THE CENTRAL TEXAS COAST.
THUNDERSTORMS ASSOCIATED WITH THIS DISTURBANCE EXTEND FARTHER
NORTH...BUT ARE MOSTLY ELEVATED. THIS SYSTEM PRODUCED OVER 10
INCHES OF RAIN ALONG PORTIONS OF THE CENTRAL TEXAS COAST LAST
NIGHT AND THIS MORNING.

THE COMPLICATING PART OF THIS UPDATE IS HOW TO DESCRIBE THE RAIN
TRENDS TONIGHT WITH THE AFOREMENTIONED FEATURES IN THE PREVIOUS
PARAGRAPHS. THE BEST WAY TO DESCRIBE THE FORECAST IS A FEW
SPRINKLES WITH A SLIGHT CHANCE OF BARELY MEASURABLE /.01 INCHES/
EARLY ON...TRENDING TOWARDS MORE STEADY RAIN IN SOME SOUTHERN
AREAS...BUT THEN ONLY A SLIGHT CHANCE OF SHOWERS FOR SEVERAL
HOURS BETWEEN SHORTWAVES...FOLLOWED BY MORE WIDESPREAD RAIN AND
SHOWERS SPREADING FROM WEST TO EAST AFTER MIDNIGHT AS ISENTROPIC
LIFT INCREASES AHEAD OF THE SECOND DISTURBANCE AND APPROACHING
SURFACE LOW. HAVING SAID THAT...HAVE PLACED WORDING OF SPRINKLES
EARLY ON IN THE ZONE FORECAST THEN TRENDED TOWARDS THE MORE
NUMEROUS TO WIDESPREAD SHOWERS IN THE WESTERN AND CENTRAL ZONES
LATER ON TONIGHT. A NOTE ABOUT THE MODELS...THE 18Z GFS WILL
VERIFY HORRIBLY WITH ITS HEAVY RAIN THAT IS SHOWS THIS EVENING
OVER SOUTHERN PORTIONS OF SOUTHEAST LOUISIANA.

LOOKING AT WINDS...THEY HAVE BEEN TRENDING A BIT LIGHTER THAN
FORECAST...SO DO NOT SEE THE REASON TO RAISE THE SMALL CRAFT
ADVISORY /SCA/ FLAGS JUST YET. THE NEXT SHIFT WILL HAVE TO
MONITOR NEW DATA AND DECIDE IF A SCA IS NEEDED ON SATURDAY.

ON SATURDAY...ALSO MADE SOME ADJUSTMENTS TO INCLUDE ISOLATED TO
SCATTERED THUNDERSTORMS OVER MAINLY COASTAL LAND AREAS AND SOME
INLAND PARISHES AND COUNTIES TO BE CONSISTENT WITH SPC. MODEL
SOUNDINGS SHOW VERY ELEVATED INSTABILITY LIFTING FROM 750-700
EARLY MORNING LOWERING TO 850-800 MB IN THE AFTERNOON BEFORE DRIER
AIR DIMINISHES THE POPS LATE IN THE AFTERNOON. IT APPEARS ANY
TRUE SURFACE BASED INSTABILITY WILL REMAIN WELL OFFSHORE EVEN IF
THE SURFACE LOW TRACKS SLIGHTLY INLAND...OWING TO THE LINGERING
EFFECTS OF CURRENT DRY AIR IN THE LOW LEVELS. WILL HAVE TO WATCH
THIS HOWEVER...AND AM STILL INDICATING THE POSSIBILITY OF STRONG
TO A FEW SEVERE STORMS NEAR THE COAST AND OFFSHORE IN THE
HAZARDOUS WEATHER OUTLOOK GIVEN THE STRENGTH OF THE MID/UPPER
SYSTEM AND THE STRONG DIFFLUENT FLOW AHEAD OF IT.

FORTUNATELY FOR US...THE EXCESSIVE RAINFALL AMOUNTS THAT FELL IN
TEXAS SHOULD NOT EVEN COME CLOSE TO SOUTHEAST LOUISIANA AND
COASTAL MISSISSIPPI...AND THE MODELS APPEAR TO HAVE A GOOD HANDLE
ON THIS SHOWING THE HIGHER AMOUNTS IN THE 1 TO 2 INCH RANGE.

UPDATED GRIDS AND TEXT PRODUCTS HAVE BEEN SENT.

22/TD

AVIATION...
MID CLOUD DECK WILL PROGRESSIVELY LOWER TO 4 TO 6 KFT BY 08-12Z
AS RAIN FALLS INTO DRIER AIR AND THE SURFACE LOW APPROACHES. RAIN
SHIELD FROM THIS FEATURE WILL GRADUALLY MOVE IN TONIGHT AN INTO
TOMORROW MORNING. CIGS WILL DROP TO MOSTLY MVFR AROUND DAYBREAK
TO MID MORNING...WITH LOWER CUGS POSSIBLE DURING CLUSTERS OF
STRONGER SHOWERS AND ANY THUNDERSTORMS. WINDS WILL GRADUALLY
INCREASE TO AROUND 10-12 KT AND REMAIN MOSTLY NORTHEAST.

PREV DISCUSSION... /ISSUED 725 PM CST FRI NOV 20 2009/ 

UPDATE...
.SOUNDING DISCUSSION...

NO PROBLEMS WITH THE FLIGHT THIS EVENING. MOISTURE CREEPING BACK
EVER SO SLOWLY WITH A PW UP TO 0.91 INCHES. STILL PLENTY OF DRY
AIR BELOW 700 MILLIBARS BUT A VERY MOIST SOUNDING ABOVE THAT
LAYER. RAINFALL AMOUNTS WILL LIKELY BE ONLY SPRINKLES AND VERY LIGHT
SHOWERS UNTIL THE LOWER LAYERS BECOME MOIST. WINDS ARE LIGHT AND
VARIABLE IN THE LOWEST LEVELS AND FROM THE SOUTHWEST ALOFT.

PREV DISCUSSION... /ISSUED 327 PM CST FRI NOV 20 2009/ 

SHORT TERM...
ADVANCING HIGH CLOUD DECK A RESULT OF LARGE CONVECTIVE FLARE-UP IN
THE WEST GULF THIS MORNING THAT HAS SINCE MOVED INTO THE MID-GULF
AND WEAKENED DURING THE PAST FEW HOURS. LARGE UPPER LEVEL
DIVERGENCE STRUCTURE WITH ADVANCING LOW PRESSURE TROUGH SWINGING
ACROSS LOWER TEXAS. PRESSURE FALLS NOTED ALONG THE LOWER TEXAS
COAST VICINITY OF BROWNSVILLE FOR WHAT APPEARS TO BE CYCLOGENESIS.
MEANWHILE...HIGH PRESSURE THAT WAS SETTLED OVER THE SOUTEASTERN
U.S. HAS WEAKENED AND RETREATED NORTHWARD...THEREBY SOFTENING THE
GRADIENT MORE THAN PREVIOUSLY EXPECTED FROM EARLIER MODEL RUNS.
GENERALLY FOLLOWING CONTINUITY OF PAST FORECASTS AND SOMEWHAT IN
LINE WITH GFS. BIGGEST UNCERTAINTIES LIE WITH FUTURE TRACK OF
SURFACE LOW...WHICH MAY BE MUCH FARTHER SOUTH THAN ANY MODELS ARE
INDICATING WITH WAKE DEPRESSION HEIGHT FALLS BEHIND CONVECTIVE
COMPLEX IN GULF CARVING A MORE APT TRAJECTORY THAN MODEL INDICATED.
IF SUCH IS THE CASE...THEN MOST OF THE LAND AREAS WILL BE
SUBJECTED TO ISENTROPIC LIFT STRATIFORM AND ELEVATED CONVECTION
FOR A DURATION OF 12 TO 18 HOURS ONSETTING AROUND MIDNIGHT IN THE
WEST AND EXITING THE EAST AROUND SATURDAY LATE AFTERNOON. THE BULK
OF SURFACE BASED CONVECTION SHOULD REMAIN OVER MARINE AREAS BUT
TRENDS WILL HAVE TO BE MONITORED CLOSELY OVERNIGHT AND
PARTICULARLY SATURDAY MORNING. CURRENT AMBIENT CONDITIONS ARE
RATHER DRY AND CONTINENTALLY INFLUENCED SO THE SATURATION PROCESS
FROM TOP-DOWN WILL BE A RATHER SLOW ONE. AFTER LOW PRESSURE
PASSAGE SATURDAY...HIGH PRESSURE SHOULD BUILD INTO THE REGION AND
MAINTAIN A LONG STRETCH OF SEASONABLY COOL TO MILD TEMPERATURES.

LONG TERM...
SEASONABLY COOL TO MILD TEMPERATURES AND GENERALLY RAIN FREE DAYS
ARE IN STORE EXCEPT FOR A BRIEF SHOT AT ISOLATED SHOWERS TUESDAY
WITH THE PASSAGE OF RE-ENFORCING COLD FRONT. MOISTURE DOES APPEAR
TO BE LIMITED WITH THIS SYSTEM. THANKSGIVING TRAVEL SHOULD BE
DEVOID OF ANY WEATHER DELAYS ACROSS THE FORECAST AREA.

MARINE... TRENDS WITH SURFACE PRESSURE GRADIENT WILL HAVE TO BE
MONITORED NEXT 12 HOURS BUT DOES APPEAR TO BE HOLD AROUND THE
15-20 KT RANGE AS LONG AS THE LOW PRESSURE SYSTEM DOES NOT DEEPEN
MUCH FURTHER THAN 1010MB UPON APPROACH. A PERIOD OF HIGHER GUSTS
IN THE 25 TO 30 KT RANGE MAY BE POSSIBLE SATURDAY LATE MORNING BUT
NOT HIGHLY CONFIDENT GIVEN THE WEAKEING GRADIENT. WILL POST
A'SMALL CRAFT EXERCISE CAUTION' HEADLINE VALID AFTER 00Z FOR THE
COASTAL AREAS AT THIS TIME WITH THE POSSIBILITY OF SMALL CRAFT
ADVISORIES IF CONDITIONS EXCEED EXPECTATIONS. AFTER LOW
PASSES...SOME ENHANCED WINDS DUE TO SHORT DURATION COLD AIR
ADVECTION INTO SUNDAY...THEN FLATTENING OUT FOR MUCH OF NEXT WEEK.
FRONTAL PASSAGE ON TUESDAY DOES NOT APPEAR TO HAVE MUCH IMPACT ON
COASTAL AREAS OTHER THAN TO RE-ENFORCE HIGH PRESSURE ALREADY IN
PLACE.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  48  58  46  64 /  60  80  40  10 
BTR  50  59  47  67 /  80  80  20  10 
MSY  55  63  52  66 /  80  80  20  10 
GPT  53  63  52  64 /  40  90  40  10 

&&

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

$$

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