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

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FXUS64 KLIX 040906
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
406 AM CDT FRI SEP 4 2015

.SHORT TERM...

NOT MUCH CHANGE IN THINKING FROM THE PREVIOUS FORECAST PACKAGE.
INCREASING NEGATIVE VORTICITY ADVECTION ASSOCIATED WITH A
DEPARTING UPPER LEVEL TROUGH SHIFTING TO THE EAST AND AN UPPER
LEVEL RIDGE BUILDING IN FROM THE WEST WILL BRING LOWER RAIN
CHANCES TO THE AREA TODAY. A NORTH-SOUTH GRADIENT WILL REMAIN IN
PLACE...WITH ONLY ISOLATED CONVECTIVE COVERAGE EXPECTED OVER THE
NORTHERN HALF OF THE FORECAST AREA...AND LOW END CHANCE POPS
AROUND 30 TO 40 PERCENT FOR THE SOUTHERN HALF OF THE AREA. COASTAL
SECTIONS OF LOUISIANA AND THE OFFSHORE WATERS WILL SEE THE BEST
CHANCES OF RAIN TODAY DUE TO INCREASED VORTICITY AND HIGHER THETA
E VALUES OVER THESE AREAS. ANY CONVECTION WILL QUICKLY DISSIPATE
AFTER SUNSET...AND EXPECT TO SEE A DRY NIGHT FOR MUCH OF THE
FORECAST AREA. ONCE AGAIN...COASTAL LOUISIANA AND THE OFFSHORE
WATERS COULD SEE ISOLATED TO SCATTERED CONVECTION THROUGH THE
NIGHT DUE TO HIGHER MOISTURE CONTENT IN THE ATMOSPHERE AND
SLIGHTLY GREATER UPPER LEVEL SUPPORT.

THE HOLIDAY WEEKEND WILL SEE THE UPPER LEVEL RIDGE GAIN SOME MORE
DOMINANCE AS THE UPPER LEVEL TROUGH AND MAIN MOISTURE AXIS SHIFTS
AWAY FROM THE AREA. ALTHOUGH THE AIRMASS ALOFT WILL TURN DRIER AS
THE RIDGE ALOFT STRENGTHENS...PW VALUES WILL STILL BE NEAR
SEASONAL NORMS OF AROUND 1.8 TO 1.9 INCHES. THERE WILL ALSO STILL
BE FAVORABLE LOW AND MID-LEVEL LAPSE RATES AND AMPLE MLCAPE OF
AROUND 2000 J/KG TO SUPPORT DIURNALLY FORCED CONVECTION EACH DAY.
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS CAN BE EXPECTED TO
FORM DURING THE LATE MORNING HOURS AND CONTINUE TO DEVELOP IN A
HIT AND MISS FASHION THROUGH THE EARLY EVENING HOURS BEFORE
DISSIPATING. TEMPERATURES WILL BE SLIGHTLY ABOVE NORMAL...WITH
HIGHS IN THE LOWER TO MIDDLE 90S AND OVERNIGHT LOWS ONLY COOLING INTO
THE MIDDLE TO UPPER 70S. THE AIRMASS WILL BE VERY MUGGY FEELING AS
DEWPOINTS REMAIN IN THE LOWER TO MIDDLE 70S THROUGH LABOR DAY.
OVERALL...A VERY TYPICAL LATE AUGUST AND EARLY SEPTEMBER AIRMASS
AND WEATHER PATTERN WILL DOMINATE FOR THE HOLIDAY WEEKEND.

.LONG TERM...

THE UPPER LEVEL TROUGH OVER THE SOUTHEASTERN CONUS WILL BEGIN TO
RETROGRADE BACK TO THE WEST BY TUESDAY AND WEDNESDAY OF NEXT WEEK.
AS THIS TROUGH AXIS SLOWLY MOVES TO THE WEST...INCREASING UPPER
LEVEL FORCING AND DEEPER ATMOSPHERIC MOISTURE PROFILES WILL
OVERSPREAD THE FORECAST AREA. TUESDAY WILL BE A TRANSITIONAL
DAY...AND STILL EXPECT TO SEE ONLY ISOLATED TO SCATTERED
CONVECTION OVER INLAND ZONES. HOWEVER...THE IMMEDIATE COAST AND
OFFSHORE WATERS COULD SEE GREATER CONVECTIVE COVERAGE AS THE DAY
GOES ON DUE TO THE INCREASE IN FORCING ALOFT AND HIGHER THETA E
VALUES ADVECTING IN FROM THE EAST. THE TREND OF INCREASING
CONVECTIVE COVERAGE WILL CONTINUE ON WEDNESDAY...AND HAVE POPS
INCREASE FROM 20 TO 30 PERCENT TO CLOSER TO 40 PERCENT FOR MOST
OF THE FORECAST AREA BY WEDNESDAY AFTERNOON.

FARTHER TO THE NORTH ON WEDNESDAY...A FAIRLY VIGOROUS SHORT WAVE
TROUGH WILL DRIVE A FRONTAL BOUNDARY INTO THE ARKLATEX BY
WEDNESDAY NIGHT. A SECONDARY UPPER LEVEL IMPULSE WILL DIVE INTO
THE MIDWEST ON THURSDAY...FORCING THIS COLD FRONT FURTHER TO THE
SOUTH...AND EXPECT TO SEE THIS BOUNDARY SWEEP INTO THE FORECAST
AREA FOR FRIDAY AND SATURDAY. AS THIS OCCURS...THE INITIAL TROUGH
THAT HAD RETROGRADED BACK OVER THE AREA WILL BE SWEPT BACK TO THE
EAST TOWARD FLORIDA AND THE SOUTHEASTERN CONUS. EVEN WITH THIS
TROUGH DEPARTING...A BROAD REGION OF INCREASING POSITIVE
VORTICITY ADVECTION IN ADVANCE OF THE DEEPENING NORTHERN STREAM
SYSTEM AND THE CONTINUED WARM AND MOIST AIRMASS OVER THE AREA
WILL ALLOW FOR HIGH END CHANCE POPS TO DEVELOP OVER THE AREA BOTH
THURSDAY AND FRIDAY. TEMPERATURES WILL COOL DUE TO THE INCREASED
CLOUD COVER AND RAINFALL...AND HAVE HIGHS ONLY CLIMBING INTO THE
UPPER 80S OVER MOST OF THE REGION.

&&

.AVIATION...

SCATTERED TS COVERAGE SHOULD BRING BRIEF MVFR CONDITIONS TODAY.
AREAL COVERAGE SHOULD BE FAIRLY SMALL NEAR TERMINALS SO VCTS WILL
SUFFICE FOR MOST TERMINALS. TONIGHT SHOULD SEE MAINLY VFR
CONDITIONS...WITH POTENTIAL FOR MVFR VISIBILITIES AT SITES THAT
RECEIVE RAIN. TIMING OF TS DEVELOPMENT SHOULD BE SIMILAR TO
YESTERDAY ~16Z.

&&

.MARINE...

A DEEP TROPICAL MOISTURE AXIS WILL REMAIN OVER THE GULF
FROM NEAR THE YUCATAN NORTHWARD TO THE NORTH CENTRAL GULF COAST.
THIS WEAKNESS WILL KEEP HIGHER CHANCES OF TS ACTIVITY IN THE COASTAL
WATERS THROUGH THE FORECAST. WINDS AND SEAS WILL BE HIGHER NEAR
SCATTERED TS. WIND GUSTS COULD BE AS HIGH AS 30 KNOTS WITH THE
STRONGEST ACTIVITY. OUTSIDE TS ACTIVITY...CONDITIONS WILL REMAIN
RATHER BENIGN WITH A WEAK PRESSURE GRADIENT. NOCTURNAL ACTIVITY WILL
BE THE MOST ABUNDANT WHILE THERE WILL BE A GENERAL DECREASE IN
ACTIVITY DURING THE LATE MORNING THROUGH LATE AFTERNOON HOURS.

&&

.DECISION SUPPORT...

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

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

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  94  72  95  72 /  20  20  30  20
BTR  93  74  94  74 /  20  20  30  20
ASD  91  75  91  74 /  20  20  30  20
MSY  88  78  90  78 /  30  30  30  20
GPT  89  76  91  75 /  20  20  30  20
PQL  91  75  91  74 /  20  20  30  20

&&

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

$$

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