Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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602
FXUS64 KLIX 272331 AAA
AFDLIX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NEW ORLEANS LA
631 PM CDT SAT SEP 27 2014

.UPDATE...
UPDATED FOR AVIATION DISCUSSION BELOW.  14/MM

&&

.AVIATION...
DRY LAYER IN THE MID LEVELS HAS RESULTED IN VERY LITTLE
PRECIPITATION THUS FAR. SHRA ARE EXPECTED TO GRADUALLY BECOME MORE
WIDESPREAD THIS EVENING AS THE ATMOSPHERE SATURATES. ACTIVITY WILL
BEGIN TO IMPACT NEW ORLEANS TERMINALS...KGPT...KASD 02-04Z AND
KBTR/KHDC AROUND 08Z. EXPECT WIDESPREAD SHRA WITH ISOLATED
THUNDER...WHICH WILL CONTINUE THROUGH THE DAY SUNDAY. MVFR
CEILINGS ARE LIKELY AT MOST OF THE TERMINALS TONIGHT/SUNDAY.
VISIBILITIES OF 1-3SM AND BRIEF WIND GUSTS 20-30 KTS WILL BE
POSSIBLE IN THE STRONGEST STORMS. ACTIVITY WILL END LATE SUNDAY
BUT LOW CEILINGS WILL BE AN ISSUE SUNDAY NIGHT/MONDAY MORNING. 14/MM

&&

.PREV DISCUSSION... /ISSUED 409 PM CDT SAT SEP 27 2014/

SHORT TERM...

THE COMBINATION OF AN ELONGATED TROUGH OF LOWER PRESSURE MOVING
NORTH FROM THE CENTRAL GULF OF MEXICO INTO THE FORECAST AREA AND A
VIGOROUS SHORT WAVE TROUGH EJECTING OUT OF SOUTHERN TEXAS TOWARD
THE CENTRAL GULF COAST WILL BE THE MAIN WEATHER FEATURES IMPACTING
THE AREA THROUGH THE WEEKEND AND INTO MONDAY. THE ELONGATED TROUGH
CURRENTLY MOVING THROUGH THE GULF WILL BRING DEEPER TROPICAL
MOISTURE AND INCREASED UPPER LEVEL FORCING INTO THE AREA FOR
TONIGHT. EXPECT TO SEE A SHIELD OF LIGHT TO MODERATE RAINFALL
SPREAD INLAND THROUGH THE OVERNIGHT HOURS...AND HAVE BUMPED UP
POPS TO CATEGORICAL FOR AREAS ALONG AND SOUTH OF A DONALDSONVILLE
TO HAMMOND TO POPLARVILLE LINE. TO THE NORTH AND WEST OF THIS LINE
HAVE PUT IN LIKELY POPS FOR TONIGHT AS FORCING AND THE AMOUNT OF
DEEPER TROPICAL MOISTURE WILL BE MORE LIMITED. LATE TONIGHT...SOME
HEAVIER RAINS MAY DEVELOP ALONG THE LOUISIANA AND MISSISSIPPI
COASTS. THESE HEAVY RAINS WILL CONTINUE INTO THE MORNING HOURS AS
THE ELONGATED TROUGH LINGERS OVER THE AREA AND SERVES AS A FOCAL
POINT FOR REPEATED HEAVIER CONVECTION.

THE VIGOROUS SHORT WAVE TROUGH WILL MOVE ACROSS THE FORECAST AREA
DURING THE DAY TOMORROW...AND WILL ALLOW FOR THE FORMATION OF A
SURFACE LOW IN A REGION OF ENHANCED BAROCLINICITY OVER THE
NORTHERN GULF. THIS LOW WILL QUICKLY RACE TO THE NORTHEAST AND
SHOULD BE FOUND OVER SOUTHERN ALABAMA BY LATE SUNDAY NIGHT. AS
THIS LOW INTENSIFIES...AND THE SHORTWAVE TROUGH PULLS TO THE
NORTHEAST...A REGION OF INCREASING SUBSIDENCE AND DRIER MID-LEVEL AIR
WILL BEGIN TO FEED INTO THE AREA. EXPECT TO SEE FAIRLY WIDESPREAD
SHOWER AND THUNDERSTORM ACTIVITY CONTINUE THROUGH THE AFTERNOON
HOURS ON SUNDAY...BUT OVERALL COVERAGE SHOULD RAPIDLY DIMINISH
DURING THE EVENING HOURS ON SUNDAY AS THE POOL OF DRY AIR IN THE
MID-LEVELS MOVES INTO THE REGION. CONDITIONS WILL FIRST IMPROVE
OVER SOUTHWEST MISSISSIPPI AND THE BATON ROUGE AREA...AND THEN
FINALLY IMPROVE BY MONDAY AFTERNOON OVER THE MISSISSIPPI AND
LOUISIANA COASTS.

LONG TERM...

A SHORT WAVE RIDGE AXIS WILL BE FOUND OVER THE LOWER MISSISSIPPI
VALLEY FOR TUESDAY...AS THE TROUGH IMPACTING THE AREA THIS
WEEKEND MOVES TOWARD THE EASTERN SEABOARD. THIS RIDGE WILL KEEP A
STABLE AIRMASS IN PLACE OVER THE AREA...DUE TO THE CONTINUED
PRESCENCE OF DRIER MID-LEVEL AIR...UPPER LEVEL SUBSIDENCE...AND A
MID-LEVEL CAP. AT MOST...SOME SCATTERED STRATO-CUMULUS DEVELOP CAN
BE EXPECTED ON TUESDAY. SINKING AIR ALOFT AND A DRIER AIRMASS
OVERALL WILL ALLOW FOR WARMER HIGHS BOTH TUESDAY AND
WEDNESDAY...AND READINGS SHOULD CLIMB INTO THE UPPER 80S BOTH
DAYS. THE BIGGEST DIFFERENCE ON WEDNESDAY WILL BE THE WEAK
BOUNDARY OFFSHORE BEGINNING TO MOVE INLAND BY LATE WEDNESDAY
AFTERNOON. THIS BOUNDARY WILL BEGIN TO FEEL THE INFLUENCE OF A
DEVELOPING LOW PRESSURE SYSTEM IN THE PLAINS AND WILL THUS BEGIN
TO MOVE NORTHWARD THROUGH THE FORECAST AREA. HAVE INCLUDED SLIGHT
CHANCE POPS FOR COASTAL AREAS OF LOUISIANA INCLUDING METRO NEW
ORLEANS. CONVECTION WILL CONTINUE TO MOVE INLAND FROM THE COASTAL
WATERS THROUGH THE NIGHT ON WEDNESDAY...AND KEEP SLIGHT CHANCE
POPS IN FOR COASTAL MISSISSIPPI AND LOUISIANA.

THURSDAY LOOKS TO BE FAIRLY UNSETTLED AND KEEP CHANCE POPS IN
PLACE ACROSS THE AREA...AS A REGION OF INCREASING POSITIVE
VORTICITY ADVECTION AND DIFLUENCE ALOFT OVERSPREAD THE GULF SOUTH.
WITH INCREASING OMEGA IN PLACE ALOFT AND THE WEAK WARM FRONTAL
BOUNDARY CONTINUES TO MOVE THROUGH THE AREA...EXPECT TO SEE
SCATTERED SHOWERS AND THUNDERSTORMS DEVELOP OVER THE AREA. THESE
CONDITIONS SHOULD PERSIST INTO THURSDAY NIGHT EVEN AS THE WARM
FRONTAL BOUNDARY MOVES FURTHER TO THE NORTH AND EAST DUE TO THE
STRONG UPPER LEVEL FORCING MOVING INTO THE REGION.

ON FRIDAY...THE SURFACE LOW WILL HAVE RACED INTO THE EASTERN GREAT
LAKES AND THE PARENT UPPER LEVEL TROUGH WILL BE SLIDING THROUGH
THE MISSISSIPPI VALLEY. A STRONG COLD FRONT WILL ACCOMPANY THIS
UPPER LEVEL TROUGH AXIS AS IT MOVES THROUGH THE AREA. THIS FRONT
WILL SERVE AS A FOCUS FOR ANOTHER ROUND OF SHOWER AND THUNDERSTORM
ACTIVITY DURING THE DAY ON FRIDAY. FORTUNATELY...THE STRONGEST
DYNAMICS WILL BE WELL NORTH OF THE FORECAST AREA...SO THE THREAT
OF SEVERE THUNDERSTORM ACTIVITY WILL BE LOW. A SECONDARY UPPER
LEVEL TROUGH WILL THEN SLIDE THROUGH FRIDAY NIGHT...PUSHING THE
FRONT WELL OFFSHORE AND ALLOWING A MUCH DRIER AND COLDER AREA OF
HIGH PRESSURE BUILD INTO THE AREA FOR SATURDAY.

MARINE...

A TIGHT PRESSURE GRADIENT REMAINS OVER THE EASTERN LEGS OF THE
COASTAL WATERS THIS AFTERNOON...AND SMALL CRAFT ADVISORY
CONDITIONS CONTINUE TO IMPACT THESE WATERS. AS THE HIGH OVER THE
SOUTHEAST WEAKENS AND A TROUGH OF LOW PRESSURE BECOMES MORE
CENTERED OVER THE AREA TONIGHT...WINDS WILL GRADUALLY WEAKEN.
EXPECT TO SEE CONTINUED EXERCISE CAUTION CONDITIONS OVER THE
EASTERN WATERS TONIGHT...BUT THEN WINDS SHOULD TURN MORE VARIABLE
TOMORROW AS A SURFACE LOW BEGINS TO DEVELOP OVER THE NORTHERN
GULF. THIS WILL PULL EAST OF THE AREA TOMORROW NIGHT...ALLOWING
WINDS TO TURN FROM A SOUTHERLY DIRECTION TO A MORE NORTHWEST
DIRECTION LATE TOMORROW NIGHT AND MONDAY. FOR THE FIRST HALF OF
NEXT WEEK...WITH A WEAK BOUNDARY LINGERING OVER THE WATERS...WINDS
WILL GENERALLY BE LIGHT AND VARIABLE THROUGH TUESDAY AND SEAS WILL
FALL TO 2 FEET OR LESS. THE WEAK BOUNDARY WILL BEGIN TO SURGE
INLAND ON WEDNESDAY AS A SURFACE LOW DEVELOPS IN THE
PLAINS...WHICH WILL ALLOW FOR A MORE SUSTAINED ONSHORE FLOW OF 5
TO 10 KNOTS TO DEVELOP WEDNESDAY AFTERNOON INTO WEDNESDAY NIGHT.

DECISION SUPPORT...

DSS CODE...GREEN.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT.

DECISION SUPPORT SERVICES (DSS) CODE LEGEND
GREEN  = NO WEATHER IMPACTS THAT REQUIRE ACTION
BLUE   = LONG FUSED WATCH/WARNING/ADVISORY IN EFFECT OR HIGH
         VISIBILITY EVENT
YELLOW = HEIGHTENED IMPACTS WITH SHORT FUSED
         WATCH/WARNING/ADVISORY ISSUANCES; RADAR SUPPORT
ORANGE = HIGH IMPACTS - SLIGHT TO MODERATE RISK SEVERE; NEARBY
         TROPICAL EVENTS; HAZMAT OR OTHER LARGE EPISODES
RED    = FULL ENGAGEMENT FOR MODERATE TO HIGH RISK SVR
         AND/OR DIRECT TROPICAL THREATS; EVENTS OF NATIONAL
         SIGNIFICANCE.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  67  82  66  85 /  60  60  40  10
BTR  69  83  68  85 /  60  60  40  10
ASD  69  82  68  85 /  80  80  50  20
MSY  73  82  71  83 /  80  80  50  20
GPT  72  82  68  83 / 100 100  60  30
PQL  71  81  67  84 / 100 100  70  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 10 PM SATURDAY FOR THE FOLLOWING
     ZONES: COASTAL WATERS FROM BOOTHVILLE LA TO THE SOUTHWEST
     PASS OF THE MISSISSIPPI RIVER OUT 20 NM...COASTAL WATERS
     FROM PASCAGOULA MS TO STAKE ISLAND LA FROM 20 TO 60
     NM...COASTAL WATERS FROM PASCAGOULA MS TO STAKE ISLAND LA
     OUT 20 NM...AND COASTAL WATERS FROM STAKE ISLAND LA TO THE
     SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60 NM.

MS...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 10 PM SATURDAY FOR THE FOLLOWING
     ZONES: COASTAL WATERS FROM BOOTHVILLE LA TO THE SOUTHWEST
     PASS OF THE MISSISSIPPI RIVER OUT 20 NM...COASTAL WATERS
     FROM PASCAGOULA MS TO STAKE ISLAND LA FROM 20 TO 60
     NM...COASTAL WATERS FROM PASCAGOULA MS TO STAKE ISLAND LA
     OUT 20 NM...AND COASTAL WATERS FROM STAKE ISLAND LA TO THE
     SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60 NM.

&&

$$







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