FXUS64 KLIX 012151
AFDLIX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
351 PM CST TUE DEC 1 2009
.SHORT TERM...
A STRONG GULF LOW CURRENTLY DEEPENING OVER THE WESTERN GULF OF
MEXICO WILL CONTINUE TO BE THE MAIN WEATHER FEATURE OF NOTE OVER
THE NEXT 72 HOURS. A BROAD SHIELD OF LIGHT TO MODERATE RAIN HAS
OVERSPREAD THE REGION...AND WILL REMAIN IN PLACE THROUGH THE LATE
EVENING HOURS. HEADING INTO TONIGHT AND EARLY TOMORROW
MORNING...THE LOW IS EXPECTED TO TRACK ACROSS SOUTHEAST LOUISIANA
AND COASTAL MISSISSIPPI.
AS THE LOW DEEPENS AND APPROACHES THE REGION...THE GRADIENT FLOW
WILL INCREASE DRAMATICALLY. THIS STRONG GRADIENT FLOW IS DUE TO A
COMBINATION OF THE DEEPENING LOW...AND A FAIRLY STRONG SURFACE
HIGH PARKED OVER THE SOUTHEASTERN STATES. WINDS OF 20 TO 30 MPH
WILL BE POSSIBLE OVER COASTAL LOUISIANA AND MISSISSIPPI DURING THE
OVERNIGHT HOURS. THE WINDS WILL BEGIN TO DIE OFF DURING THE DAY
TOMORROW...AS THE LOW QUICKLY PULLS OFF TO THE NORTHEAST. IN
ADDITION TO THE WIND...IT APPEARS THAT A RISK OF STRONG TO
POSSIBLY SEVERE THUNDERSTORMS COULD DEVELOP OVER COASTAL LOUISIANA
LATE TONIGHT. OVERALL INSTABILITY PARAMETERS REMAIN VERY
WEAK...WITH CAPE VALUES OF 500 J/KG OR LESS. HOWEVER...STRONG LOW
LEVEL SHEAR WILL ALLOW FOR A RISK OF STRONG WINDS AND ISOLATED
TORNADOES OVERNIGHT. IT APPEARS THAT EXTREME COASTAL LOUISIANA
WILL HAVE THE BEST CHANCE OF ANY SEVERE WEATHER TONIGHT. A THIRD
CONCERN WILL BE THE POSSIBILITY OF SOME COASTAL FLOODING OUTSIDE
OF THE PROTECTION LEVEES. STRONG EASTERLY FLOW OVER THE NEXT 12
HOURS SHOULD PUSH TIDES ABOUT 1 TO 2 FEET ABOVE NORMAL ALONG EAST
FACING SHORES. HOWEVER...GIVEN THE SHORT DURATION OF STRONGER
WINDS...MORE SIGNIFICANT COASTAL FLOODING IS NOT EXPECTED. DUE TO
THIS...HAVE ONLY WENT WITH AN ADVISORY AND NOT A WARNING FOR
COASTAL FLOODING.
A FINAL IMPACT FROM THIS STRONG GULF LOW WILL BE HEAVY RAINFALL.
THE LIGHT TO MODERATE STRATIFORM PRECIPITATION SHOULD BE REPLACED
BY A HEAVIER RAINFALL AND SOME ELEVATED CONVECTION. THESE ELEVATED
THUNDERSTORMS COULD DUMP VERY HEAVY RAINFALL OF 2 TO 3 INCHES IN A
SHORT AMOUNT OF TIME. DUE TO THE RISK OF HEAVY RAINS FROM THESE
THUNDERSTORMS...HAVE WENT WITH A FLASH FLOOD WATCH FOR COASTAL
MISSISSIPPI AND LOUISIANA. IN ADDITION...DRAINAGE MAY BE SLOWED BY
THE HIGHER THAN NORMAL TIDES.
THE SURFACE LOW WILL LIFT INTO THE SOUTHERN APPALACHIANS BY
WEDNESDAY AFTERNOON. HOWEVER...A VERY STRONG UPPER LEVEL LOW WILL
BE TRANSITING THROUGH THE LOWER MISSISSIPPI VALLEY. THIS COLD
UPPER LEVEL FEATURE SHOULD PROVIDE ENOUGH INSTABILITY TO PRODUCE A
FEW SHOWERS AND KEEP LINGERING CLOUD COVER OVER THE AREA THROUGH
WEDNESDAY EVENING. SKIES WILL RAPIDLY CLEAR WEDNESDAY NIGHT...AS
STRONG SUBSIDENCE IN THE WAKE OF THE UPPER LEVEL LOW ADVECTS INTO
THE REGION. THESE CLEAR SKIES AND DRY CONDITIONS WILL PERSIST
THROUGH THURSDAY NIGHT.
.LONG TERM...
HEADING INTO THE WEEKEND...LARGE DISAGREEMENTS BETWEEN THE GFS AND
EURO MODELS DEVELOP. HOWEVER...THESE DISAGREEMENTS ARE MOSTLY
CONFINED TO THE LOW LEVELS...AND THE DEVELOPMENT OF ANOTHER GULF
LOW HEADING INTO FRIDAY NIGHT AND SATURDAY. IN THE UPPER
LEVELS...BOTH MODELS ARE IN VERY GOOD AGREEMENT THAT A STRONG AND
DEEP UPPER LEVEL TROUGH WILL DIVE THROUGH THE PLAINS STATES AND
INTO THE GULF SOUTH. THE MAIN TROUGH AXIS SHOULD PASS THROUGH THE
AREA FRIDAY NIGHT...ALONG WITH A VERY STRONG FRONTAL BOUNDARY.
BOTH MODELS ARE ALSO IN GOOD AGREEMENT...THAT STRONG COLD AIR
ADVECTION IN THE WAKE OF A COLD FRONT FRONT PROGGED TO SWEEP
THROUGH FRIDAY NIGHT WILL TAKE PLACE. TEMPERATURES WILL DROP BELOW
FREEZING ACROSS THE NORTHERN THIRD OF THE FORECAST AREA FOR FRIDAY
AND SATURDAY NIGHTS. DAYTIME HIGHS WILL BE A GOOD 10 DEGREES BELOW
NORMAL AS THIS DEEP COLD POOL SLIDES THROUGH THE REGION. THE MAIN
DIFFERENCE ARISES WITH THE AMOUNT OF CYCLOGENESIS EXPECTED WITH
THIS APPROACHING TROUGH. THE GFS IS VERY AGRESSIVE AND QUICKLY
SPINS UP ANOTHER DEEP LOW PRESSURE SYSTEM IN THE CENTRAL GULF OF
MEXICO. THIS STRONG LOW WRAPS DEEP TROPICAL MOISTURE UP INTO THE
GULF SOUTH...JUST AS THE COLDER AIR BEGINS TO BLEED INTO THE
REGION. BASED ON THIS FORECAST...SOME TYPE OF WINTER PRECIPITATION
WOULD BE POSSIBLE. HOWEVER...THE ECMWF HAS A MUCH WEAKER LOW FORM
IN THE CENTRAL GULF. MOISTURE IS LIMITED ALONG THE FRONT...AND
EXITS THE REGION WELL BEFORE THE COLDEST AIR MOVES IN. THIS
SCENARIO WOULD KEEP ANY WINTER WEATHER OUT OF THE FORECAST. GIVEN
THE HIGH UNCERTAINTY OF THE SITUATION...HAVE DECIDED TO KEEP THE
ONGOING FORECAST IN PLACE AND WAIT FOR ADDITIONAL GUIDANCE OVER
THE NEXT DAY OR SO.
IN EITHER EVENT...A COLD AND DRY LOW LEVEL AIRMASS WILL SETTLE
OVER THE FORECAST AREA SATURDAY AND SUNDAY. IN THE UPPER
LEVELS...THE PATTERN WILL TURN MORE ZONAL AS THE DEEP TROUGH OVER
THE EASTERN SEABOARD QUICKLY LIFTS TO THE NORTH AND EAST. SOME
WEAK WARM AIR AND MOISTURE ADVECTION WILL DEVELOP SUNDAY NIGHT
AS ANOTHER FAST MOVING SHORT WAVE TROUGH APPROACHES. AS THIS
WARMER AIR MEETS THE COLDER LOW LEVEL AIRMASS...SOME WEAK
ISENTROPIC LIFT WILL TAKE HOLD. INCREASING CLOUDS AND A FEW
SHOWERS WILL BE POSSIBLE BY LATE SUNDAY NIGHT. THE SHORT WAVE WILL
SWEEP THROUGH MONDAY INTO MONDAY...AND HAVE DECIDED TO GO WITH LOW
END CHANCE POPS TO REFLECT THE PASSAGE OF THIS SYSTEM. A VERY
ZONAL FLOW WILL SET UP FOR MONDAY NIGHT AND TUESDAY...WITH A BROAD
AREA OF LIFT EXPECTED TO REMAIN OVER THE REGION. WITH THIS IN
MIND...HAVE KEPT A CHANCE OF RAIN IN THROUGH TUESDAY.
&&
.AVIATION...
IN GENERAL...IFR CONDITIONS WILL PREVAIL TONIGHT AND WEDNESDAY AT
EACH OF THE TAFS SITES DUE TO LOW CEILINGS AND OCCASIONAL RAIN.
THERE MAY BE TIMES THIS EVENING WHEN CONDITIONS IMPROVE TO MVFR.
THERE WILL BE AN IMPROVING TREND COMMENCING LATE WEDNESDAY MORNING
AND CONTINUING INTO THE AFTERNOON AS THE RAIN TAPERS OFF AND CEILINGS
GRADUALLY RISE INTO THE MVFR CATEGORY. WINDS WILL BE GUSTY AT
TIMES...ESPECIALLY AT KMSY AND KGPT. 11
&&
.MARINE...
GALE OR NEAR GALE CONDITIONS ARE EXPECTED TO DEVELOP THIS EVENING
ACROSS THE GULF COASTAL WATERS AND CONTINUE THROUGH WEDNESDAY AS LOW
PRESSURE IN THE NORTHWEST GULF MOVE NORTHEAST TOWARD THE SOUTH
LOUISIANA COAST THIS EVENING AND MOVES ACROSS THE COASTAL SECTIONS
OF SOUTHEAST LOUISIANA AND SOUTH MISSISSIPPI LATE TONIGHT AND
WEDNESDAY MORNING. SMALL CRAFT CONDITIONS WILL PREVAIL ACROSS THE
TIDAL LAKES DURING THE SAME PERIOD. WINDS WILL GRADUALLY DIMINISH
WEDNESDAY NIGHT AND THURSDAY AS HIGH PRESSURE SETTLES ACROSS THE
GULF COAST REGION. WINDS MAY PICK UP AGAIN LATE IN THE WEEK AS
ANOTHER AREA OF LOW PRESSURE POSSIBLY DEVELOPS AND TRACKS NORTHEAST
ACROSS THE CENTRAL GULF. 11
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 47 57 38 55 / 80 20 0 0
BTR 48 59 40 57 / 80 20 0 0
MSY 52 64 45 57 / 100 20 0 0
GPT 50 64 42 58 / 100 40 0 0
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...COASTAL FLOOD ADVISORY UNTIL 6 AM WEDNESDAY FOR THE FOLLOWING
ZONES: LOWER JEFFERSON...LOWER LAFOURCHE...LOWER
PLAQUEMINES...LOWER ST. BERNARD...LOWER
TERREBONNE...ORLEANS...ST. TAMMANY...AND UPPER ST. BERNARD.
FLASH FLOOD WATCH FROM 6 PM TUESDAY TO NOON WEDNESDAY FOR THE
FOLLOWING ZONES: ASSUMPTION...LOWER JEFFERSON...LOWER
LAFOURCHE...LOWER PLAQUEMINES...LOWER ST. BERNARD...LOWER
TERREBONNE...ORLEANS...ST. CHARLES...ST. JAMES...ST. JOHN
THE BAPTIST...ST. TAMMANY...UPPER JEFFERSON...UPPER
LAFOURCHE...UPPER PLAQUEMINES...UPPER ST. BERNARD...AND
UPPER TERREBONNE.
GM...SMALL CRAFT ADVISORY UNTIL 9 PM WEDNESDAY FOR THE FOLLOWING
ZONES: AND LAKE PONTCHARTRAIN AND LAKE MAUREPAS.
GALE WARNING UNTIL 9 PM WEDNESDAY FOR THE FOLLOWING ZONES:
COASTAL WATERS FROM PASCAGOULA MS TO THE SOUTHWEST PASS OF
THE MISSISSIPPI RIVER FROM 20 TO 60 NM...COASTAL WATERS
FROM PASCAGOULA MS TO THE SOUTHWEST PASS OF THE MISSISSIPPI
RIVER OUT 20 NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF
THE MISSISSIPPI RIVER TO LOWER ATCHAFALAYA RIVER LA FROM 20
TO 60 NM...AND COASTAL WATERS FROM THE SOUTHWEST PASS OF
THE MISSISSIPPI RIVER TO LOWER ATCHAFALAYA RIVER LA OUT 20
NM.
MS...FLASH FLOOD WATCH FROM 6 PM TUESDAY TO NOON WEDNESDAY FOR THE
FOLLOWING ZONES: HANCOCK...HARRISON...JACKSON...AND PEARL
RIVER.
COASTAL FLOOD ADVISORY UNTIL 6 AM WEDNESDAY FOR THE FOLLOWING
ZONES: HANCOCK...HARRISON...AND JACKSON.
GM...SMALL CRAFT ADVISORY UNTIL 9 PM WEDNESDAY FOR THE FOLLOWING
ZONES: AND LAKE PONTCHARTRAIN AND LAKE MAUREPAS.
GALE WARNING UNTIL 9 PM WEDNESDAY FOR THE FOLLOWING ZONES:
COASTAL WATERS FROM PASCAGOULA MS TO THE SOUTHWEST PASS OF
THE MISSISSIPPI RIVER FROM 20 TO 60 NM...COASTAL WATERS
FROM PASCAGOULA MS TO THE SOUTHWEST PASS OF THE MISSISSIPPI
RIVER OUT 20 NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF
THE MISSISSIPPI RIVER TO LOWER ATCHAFALAYA RIVER LA FROM 20
TO 60 NM...AND COASTAL WATERS FROM THE SOUTHWEST PASS OF
THE MISSISSIPPI RIVER TO LOWER ATCHAFALAYA RIVER LA OUT 20
NM.
&&
$$
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