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

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295
FXUS64 KLIX 200107
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
807 PM CDT THU MAR 19 2015

...SOUNDING DISCUSSION...
THE SOUNDING THIS EVENING HAS SOUTHWESTERLY WINDS AT THE SFC THEN
BECOME WESTERLY BY 025 FT. PEAK WIND IS 75 KTS AT 225 MB. THE
PROFILE APPROACHES SATURATION AT A COUPLE POINTS IN LAYERS WITH
SCATTERED CLOUDS... NEAR 880 MB... 700 MB... AND 375 MB. PW IS
WELL ABOVE AVERAGE AT 1.5 INCHES.

KRAUTMANN

&&

.PREV DISCUSSION... /ISSUED 345 PM CDT THU MAR 19 2015/

SHORT TERM...

WEAK UPPER LEVEL RIDGING EXTENDING ACROSS THE GULF SOUTH REMAINS
IN CONTROL OF THE AREA...AND WILL CONTINUE TO DO SO THROUGH
TOMORROW. WITH THIS RIDGING IN PLACE ALOFT...A FAIRLY POTENT CAP
IS NOTED FROM THE MORNING SOUNDING AND IN THE MODEL SOUNDINGS AS
WELL. THIS CAP WILL EFFECTIVELY LIMIT MOST CONVECTIVE POTENTIAL
THROUGH TOMORROW...AND ONLY HAVE SLIGHT CHANCE POPS FOR THE REST
OF TODAY AND TONIGHT ACROSS THE AREA. TOMORROW...SLIGHT CHANCE
POPS WILL CONTINUE IN THE MORNING...BUT AS THE RIDGE BEGINS TO
WEAKEN SLIGHTLY DURING THE AFTERNOON HOURS SOME MORE SCATTERED
CONVECTION COULD FORM FAR INLAND ZONES. THIS WEAKENING OF THE
RIDGE ALOFT WILL BE DUE TO INCREASING POSITIVE VORTICITY ADVECTION
TAKING HOLD IN ADVANCE OF AN APPROACHING SOUTHERN STREAM TROUGH.

OUTSIDE OF THE LOW RAIN CHANCES...THE BIGGEST CONCERN WILL THE
RISK OF FOG FORMING BOTH TONIGHT AND TOMORROW NIGHT. CONDITIONS
WILL BE PRIMED FOR FOG DUE TO THE COMBINATION OF BOUNDARY LAYER
WINDS OF AROUND 5 KNOTS...HIGH DEWPOINTS AND RESULTANT RELATIVE
HUMIDITIES...OVERNIGHT LOWS FALLING BELOW THE CRITICAL CROSS-OVER
TEMPERATURE. HAVE INCLUDED AREAS OF FOG IN THE FORECAST FOR
TONIGHT AND TOMORROW NIGHT...AND EXPECT TO SEE SOME PATCHY DENSE
FOG DEVELOP AROUND DAYBREAK. HAVE DECIDED TO HOLD OFF ON ISSUING A
DENSE FOG ADVISORY FOR NOW...BUT THIS WILL NEED TO MONITORED
THROUGH THE NIGHT.

THE SOUTHERN STREAM TROUGH WILL FINALLY BEGIN TO PULL INTO THE
SOUTHERN PLAINS ON SATURDAY. THIS TROUGH WILL BE FAIRLY WEAK AND
RETAIN A POSITIVE TILT...AND OVERALL SHEAR VALUES ARE VERY LIMITED
WITH THIS FEATURE. GIVEN THIS...DO NOT EXPECT TO SEE A SEVERE
WEATHER THREAT WITH THIS SYSTEM. HOWEVER...A BROAD AREA OF HIGHER
OMEGA AND AMPLE WARMTH AND MOISTURE WILL BRING PERIODS OF SHOWERS
AND THUNDERSTORMS TO THE ENTIRE FORECAST AREA BEGINNING ON
SATURDAY AND PERSISTING THROUGH THE DAY ON SUNDAY. CONDITIONS ON
SATURDAY WILL LARGELY BE DRIVEN BY WARM FRONTAL PROCESSES IN
ADVANCE OF A DEVELOPING SURFACE LOW. SCATTERED SHOWERS IN THE
MORNING WILL TURN MORE NUMEROUS DURING THE AFTERNOON AND EVENING
HOURS...AND SOME SCATTERED THUNDERSTORMS WILL BE POSSIBLE DURING
THE PEAK HEATING HOURS IN THE AFTERNOON AND EVENING. THESE
CONDITIONS WILL PERSIST INTO SATURDAY NIGHT AS THE TROUGH AND
ATTENDANT SURFACE LOW CONTINUE TO APPROACH THE LOWER MISSISSIPPI
VALLEY. THE ONE LIMITING COMPONENT FOR SUSTAINED THUNDERSTORMS
OVERNIGHT WILL BE WEAK LAPSE RATES THROUGH THE ATMOSPHERIC COLUMN.

HEADING INTO SUNDAY...CONDITIONS WILL TURN MORE FAVORABLE FOR
THUNDERSTORMS TO FORM AS A DRYLINE SURGES EASTWARD FROM TEXAS AND
MOVES THROUGH THE FORECAST AREA THROUGH THE DAY.
ADDITIONALLY...WITH THE MAIN UPPER LEVEL LOW MOVING
THROUGH...LAPSE RATES IN THE MID AND UPPER LEVELS WILL IMPROVE
DRAMATICALLY...AND EXPECT TO SEE FORECAST CAPE VALUES APPROACH
1000 J/KG DURING THE AFTERNOON. THE COMBINATION OF INCREASED
FORCING ALONG THE LOW LEVEL BOUNDARY AND AMPLE CONVECTIVE
INSTABILITY WILL SUPPORT THE DEVELOPMENT OF SOME DEEPER
CONVECTION AND STRONGER THUNDERSTORMS SUNDAY AFTERNOON. THE ONE
FACTOR LIMITING ANY CONVECTION WILL BE A LACK OF SHEAR OVER THE
AREA. THIS SHOULD KEEP ANY STORMS FROM ACHIEVING ENOUGH VERTICAL
TILT TO ATTAIN SEVERE STATUS. AS THE DRYLINE SURGES TO THE EAST
THROUGH THE EVENING HOURS ON SUNDAY...RAIN CHANCES WILL COME TO AN
END FROM WEST TO EAST.

LONG TERM...

STRONG SUBSIDENCE AND NEGATIVE VORTICITY ADVECTION IN THE WAKE OF
THE TROUGH WILL BRING RAPIDLY CLEARING SKIES AND DRY WEATHER TO
THE REGION ON MONDAY. TEMPERATURES WILL COOL SLIGHTLY...BACK TO
MORE SEASONAL LEVELS...BUT NO STRONG SURGE OF COLD AIR ADVECTION
IS EXPECTED AS THE AIRMASS MOVING IN WILL BE PACIFIC BASED. THESE
SEASONAL TEMPERATURES AND CLEAR SKIES WILL PERSIST INTO TUESDAY AS
A BROAD AREA OF UPPER LEVEL RIDGING BUILDS OVER THE REGION.

THE UPPER LEVEL FLOW REGIME WILL TURN MORE ZONAL ON WEDNESDAY AND
THURSDAY AS A SERIES OF WEAK UPPER LEVEL IMPULSES SLIDES THROUGH
THE MIDWESTERN STATES AND FLATTENS OUT OF THE UPPER LEVEL RIDGE
OVER THE GULF SOUTH. OVERALL...THERE WILL BE LITTLE IN THE WAY OF
SENSIBLE WEATHER ON WEDNESDAY...WITH ONLY SLIGHTLY WARMER
TEMPERATURES AND A BIT MORE LOW LEVEL CLOUD DEVELOPMENT EXPECTED.
BY THURSDAY...A WEAK FRONTAL BOUNDARY WILL SLOWLY SLIP INTO THE
AREA IN RESPONSE TO THE NEXT PASSING UPPER LEVEL IMPULSE IN THE
MIDWEST. THIS WEAK FRONT SHOULD SERVE AS A FOCUS FOR SOME ISOLATED
TO SCATTERED CONVECTION ON THURSDAY. GIVEN THE LACK OF STRONG
OMEGA AND SHEAR VALUES EXPECTED OVER THE AREA...ANY THUNDERSTORMS
LOOK TO BE WEAK AT THIS TIME.

AVIATION...

ISOLATED SHRA ARE EXPECTED TO REMAIN ISOLATED IN MOST LOCATIONS
THROUGH ABOUT 01Z...HOWEVER AN AIRPORT OR TWO COULD HAVE SOME BRIEF
IMPACTS WITH CIGS AROUND 030 AND LOWERED VSBYS. THE MAIN CONCERN IS
FOR LOW STRATUS AND FOG LATE TONIGHT INTO FRIDAY MORNING WHICH
APPEARS LIKELY...AND LIFR CONDITIONS ARE IN THE TAFS.

22/TD

MARINE...

VERY BENIGN CONDITIONS WILL CONTINUE TO DOMINATE THE MARINE ZONES
THROUGH SATURDAY WITH LIGHT AND VARIABLE WINDS OF 10 KNOTS OR LESS
AND SEAS OF 2 FEET OR LESS EXPECTED. CONDITIONS WILL DETERIORATE
ON SUNDAY...AS A FRONTAL BOUNDARY MOVES OFFSHORE AND A WEAK AREA
LOW PRESSURE SLIDES BY. WINDS WILL INCREASE INTO EXERCISE CAUTION
RANGE BY SUNDAY NIGHT AND PERSIST INTO THURSDAY AND A SLIGHTLY
STRONGER PRESSURE GRADIENT BETWEEN A RIDGE MOVING INTO THE
SOUTHEAST AND A BROADER AREA OF LOW PRESSURE IN THE WESTERN GULF
INTERACT.

DECISION SUPPORT...

DSS CODE...GREEN.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
           MONITORING DENSE FOG POTENTIAL NEXT TWO NIGHTS/MORNINGS.

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 TONIGHT RISK SVR
         AND/OR DIRECT TROPICAL THREATS; EVENTS OF NATIONAL
         SIGNIFICANCE

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  78  62  78  62 /  20  20  30  30
BTR  81  63  80  63 /  20  20  20  20
ASD  80  63  78  63 /  20  20  20  20
MSY  80  63  79  64 /  20  20  20  20
GPT  77  63  79  63 /  20  20  20  20
PQL  80  63  80  62 /  20  20  20  20

&&

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

$$



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