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

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275
FXUS64 KLIX 170100
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
700 PM CST TUE DEC 16 2014

.SOUNDING DISCUSSION...

ROUTINE FLIGHT TERMINATED OVER MISSISSIPPI SOUND SOUTH OF
PASCAGOULA JUST NORTH OF THE EAST END OF HORN ISLAND. BALLOON
BURST AT 110.2K FEET...OR ABOUT 20.9 MILES UP.

AIRMASS HAS DRIED OUT SIGNIFICANTLY OVER THE LAST 24 HOURS...WITH
PRECIPITABLE WATER VALUES NOW DOWN TO 0.38 INCHES...ABOUT 45
PERCENT OF NORMAL...COMPARED TO 1.18 LAST EVENING. INVERSIONS FROM
ABOUT 940 MB TO AROUND 750 MB THIS EVENING...ASIDE FROM THE
SURFACE INVERSION BEGINNING TO DEVELOP. NORTHWEST WINDS AT THE
SURFACE BECOME WESTERLY BY 700 MB...AND REMAIN WESTERLY THROUGH
THE TROPOPAUSE. WIND MAX BELOW 100 MB WAS 67 KNOTS AT 38.2K FEET.
35

&&

.PREV DISCUSSION... /ISSUED 357 PM CST TUE DEC 16 2014/

SHORT TERM...

DEEP LAYER RIDGING WILL CONTINUE TO DOMINATE THE FORECAST AREA
THROUGH TONIGHT...WITH CLEAR SKIES AND A DRY AIRMASS EXPECTED.
WITH CLEAR SKIES AND LIGHT WINDS IN PLACE...TEMPERATURES WILL BOTTOM OUT
TONIGHT. LOWS ARE EXPECTED TO FALL INTO THE MIDDLE AND UPPER 30S
FOR MOST AREAS AWAY FROM THE COAST AND TIDAL LAKES.

HEADING INTO TOMORROW...THE RIDGE AXIS WILL START TO SLIDE TO THE
EAST OF THE REGION...AND A WEAK ONSHORE FLOW WILL DEVELOP IN THE
LOW LEVELS. THERE WILL BE SOME INCREASED MOISTURE INTO THE
AREA...AND CLOUDS WILL BE ON THE INCREASE DURING THE AFTERNOON.
A WEAK ELONGATED VORT MAX WILL SLIDE THROUGH THE MID-SOUTH
WEDNESDAY NIGHT INTO THURSDAY...WHICH WILL BRING AN INCREASE IN
MID AND UPPER LEVEL MOISTURE WITH IT. AS MOISTURE ALOFT
RISES...THE AMOUNT OF CLOUD COVER OVER THE NORTHERN HALF OF THE
FORECAST WILL INCREASE WEDNESDAY NIGHT. MOSTLY CLOUDY CONDITIONS
ARE EXPECTED OVER THE NORTHERN AND WESTERN PORTIONS OF THE CWA BY
THURSDAY. THE ELONGATED VORT WILL ALSO KEEP A REGION OF INCREASED
UPPER LEVEL OMEGA OVER THE NORTHWEST PART OF THE FORECAST AREA ON
THURSDAY. THIS SHOULD ALLOW FOR SCATTERED RAIN SHOWERS TO DEVELOP
OVER THIS AREA THROUGH THE DAY. TEMPERATURES WILL BE NEAR NORMAL
AS A LARGELY ZONAL FLOW REGIME DOMINATES THE GULF SOUTH.

WITH THIS ZONAL FLOW PATTERN DOMINATING THE GULF SOUTH...ANOTHER
MUCH STRONGER SHORTWAVE FEATURE WILL KICK OUT OF THE FOUR CORNERS
AND INTO TEXAS THURSDAY NIGHT. AS THE UPPER LEVEL LOW MOVES INTO
TEXAS...JET DYNAMICS ALOFT WILL CREATE A FAVORABLE AREA FOR LOW
LEVEL CYCLOGENESIS TO OCCUR OVER EASTERN TEXAS. THIS LOW WILL
CONTINUE TO DEEPEN AS IT MOVES TO THE EAST ACROSS THE FORECAST
AREA ON FRIDAY. IN ADVANCE OF THE LOW...EXPECT TO SEE A WARM FRONT
SURGE INLAND FROM THE NORTHERN GULF. THIS WARM FRONT SHOULD EXTEND
FROM CENTRAL LOUISIANA ACROSS SOUTHWEST MISSISSIPPI AND INTO
CENTRAL ALABAMA BY FRIDAY AFTERNOON. THIS WILL PLACE THE VAST
MAJORITY OF THE FORECAST AREA SOUTH OF THE WARM FRONT...OR IN A
REGION OF WARMER AND MORE UNSTABLE AIR. OVERALL INSTABILITY WILL
BE FAIRLY MARGINAL...WITH SKINNY CAPE EXPECTED SOUTH OF THE I-10
CORRIDOR. HOWEVER...SHEAR VALUES WILL VERY HIGH AS A 40 KNOT LOW
LEVEL JET DEVELOPS ACROSS THE REGION. 0-3KM SPEED SHEAR WILL
AVERAGE 30 TO 35 KNOTS AND HELICITY VALUES WILL BE WELL IN EXCESS
OF 300 M2/S2. THIS WILL BE A CLASSIC LOW CAPE-HIGH SHEAR
SCENARIO...WHERE THE MOST LIKELY CONVECTIVE MODES WILL BE STRONG
WINDS AND ISOLATED TORNADOES. THE MOST LIKELY REGION FOR SURFACE
BASED SEVERE WEATHER IMPACTS WILL BE ALONG THE LOUISIANA COAST AND
OFFSHORE WATERS FRIDAY AFTERNOON AND EVENING. THERE COULD BE AN ISOLATED
SEVERE WEATHER EVENT IN THE NEW ORLEANS METRO AREA AS WELL DURING
THIS PERIOD OF TIME.

FRIDAY NIGHT...THE SEVERE THREAT WILL SHIFT TOWARD THE OFFSHORE
WATERS EAST OF THE MISSISSIPPI AS WELL AS THE MISSISSIPPI COAST.
STRONG SHEAR VALUES WILL REMAIN OVER THIS AREA...WITH HELICITY
VALUES IN EXCESS OF 250 M2/S2 ON THE MISSISSIPPI COAST. OVERALL
INSTABILITY WILL BE WEAKER...BUT AN ISOLATED SEVERE WEATHER EVENT
CANNOT BE RULED ALONG THE IMMEDIATE COAST. FARTHER TO THE
WEST...WINDS WILL SHIFT TO THE WEST AND DRIER AIR WILL SLOWLY
BEGIN TO ADVECT INTO THE MID-LEVELS. EXPECT TO SEE LINGERING LOW
LEVEL STRATUS AND SHOWERS THROUGH THE NIGHT AND INTO EARLY
SATURDAY MORNING. BY SATURDAY AFTERNOON...ONLY A FEW SHOWERS WILL
LINGER OVER COASTAL MISSISSIPPI WITH CLEARING SKIES AND DRY
WEATHER EXPECTED ACROSS SOUTHEAST LOUISIANA AND SOUTHWEST
MISSISSIPPI. TEMPERATURES WILL DROP FROM THE LOW TO MID 70S ON
FRIDAY TO THE LOW TO MID 60S ON SATURDAY. BASICALLY READINGS WILL
FALL BACK TO MORE SEASONAL NORMS.

LONG TERM...

THE ZONAL FLOW PATTERN WILL CONTINUE TO DOMINATE ON SUNDAY...BUT A
MUCH DRIER AIRMASS WILL ADVECT INTO THE LOW AND MID-LEVELS. AS A
RESULT...MOSTLY CLEAR SKIES AND DRY WEATHER ARE EXPECTED THROUGH
THE DAY. HOWEVER...MODELS SHOW ANOTHER ELONGATED TROUGH AXIS
MOVING INTO THE SOUTHERN PLAINS SUNDAY. BOTH THE EURO AND GFS MODELS
INDICATE THAT A JET STREAK WILL ROUND THE BASE OF THE TROUGH
SUNDAY NIGHT AND CAUSE THE TROUGH TO ACCELERATE EASTWARD MONDAY
AND TUESDAY. A SURFACE LOW IS EXPECTED TO DEVELOP IN A REGION OF
ENHANCED BAROCLINICITY OVER THE WESTERN GULF AS THIS JET STREAK
ROUNDS THE BASE OF THE TROUGH. THE SURFACE LOW WILL THEN RACE
EASTWARD ACROSS THE CENTRAL GULF TOWARD FLORIDA MONDAY AND
TUESDAY. AS THE LOW PASSES TO THE SOUTH OF THE FORECAST AREA...SOME
ISENTROPICALLY INDUCED PRECIPITATION TO THE NORTH OF A WEAK
SURFACE BOUNDARY IN THE GULF COULD DEVELOP ALONG THE IMMEDIATE
COAST AND OVER THE OFFSHORE WATERS. HAVE KEPT IN A SLIGHT CHANCE
OF POPS FOR THESE AREAS FROM SUNDAY NIGHT THROUGH MONDAY NIGHT.
OTHERWISE...MAINLY CLEAR SKIES...COOL TEMPERATURES...AND DRY
WEATHER ARE EXPECTED EARLY NEXT WEEK.

AVIATION...

DRY AIR WILL RESULT IN VFR CONDITIONS WITH MOSTLY CLEAR SKIES AND
EXCELLENT VISIBILITIES THROUGH WEDNESDAY. NORTHWEST WINDS MAY
OCCASIONALLY GUST 15 TO 20 KNOTS THROUGH SUNSET TODAY...OTHERWISE
PREVAILING WINDS WILL BE MOSTLY 10 KNOTS OR LESS. 22/TD

MARINE...

NORTHWEST FLOW OF 10 TO 15 KNOTS WILL EAST AND TURN MORE EASTERLY
THROUGH TOMORROW AS A SURFACE HIGH SETTLES OVER THE GULF SOUTH.
SEAS WILL ALSO DROP FROM 2 TO 3 FEET TO 1 TO 2 FEET BY TOMORROW
AFTERNOON. THESE LIGHT EAST AND SOUTHEAST WINDS WILL LINGER INTO
THURSDAY...BUT WILL BEGIN TO INCREASE TO 10 TO 15 KNOTS BY
THURSDAY NIGHT AS A LOW PRESSURE SYSTEM DEVELOP OVER EASTERN
TEXAS. THE GRADIENT WILL CONTINUE TO TIGHTEN ON FRIDAY...AND
EXPECT TO SEE SOUTHEAST AND SOUTHERLY WINDS OF 15 TO 20 KNOTS AND
ROUGH SEAS FRIDAY INTO FRIDAY NIGHT. AS THE LOW PULLS TO THE EAST
ON SATURDAY...WIND WILL VEER TO THE WEST AND NORTHWEST AT 15 TO 20
KNOTS. CONDITIONS WILL BEGIN TO IMPROVE SUNDAY AS THE GRADIENT
WEAKENS. EXPECT TO SEE A NORTHEAST WIND OF 10 TO 15 KNOTS BY
SUNDAY AFTERNOON.

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  35  61  40  65 /   0   0   0  20
BTR  39  62  44  69 /   0   0   0  10
ASD  36  61  40  67 /   0   0   0  10
MSY  43  59  45  67 /   0   0   0  10
GPT  38  61  42  68 /   0   0   0  10
PQL  37  61  38  67 /   0   0   0  10

&&

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

$$







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