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

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212
FXUS64 KLIX 210907
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
407 AM CDT SUN SEP 21 2014

.SHORT TERM...

NORTHWEST FLOW WILL REMAIN IN PLACE IN THE MID AND UPPER LEVELS OF
THE ATMOSPHERE THROUGH TUESDAY DUE TO A PERSISTENT UPPER LEVEL
TROUGH DOMINATING THE EASTERN THIRD OF THE CONUS. WITH THIS FLOW
PATTERN IN PLACE...A REINFORCING COLD FRONT WILL SWEEP THROUGH THE
REGION ON MONDAY. THIS FRONT WILL HAVE LITTLE IN THE WAY OF
MOISTURE TO WORK WITH...AND ONLY EXPECT TO SEE ISOLATED CONVECTION
DEVELOP AS IT MOVES THROUGH. THIS CONVECTION WILL BE FOCUSED
IMMEDIATELY ALONG THE FRONT WHERE OVERALL FORCING WILL BE
GREATEST. OUTSIDE OF THE PASSING FRONT...A DRY FORECAST IS IN
PLACE FOR ALL OF THE LAND BASED ZONES THROUGH TUESDAY. IN THE GULF
WATERS...SLIGHTLY HIGHER LOW LEVEL MOISTURE CONTENT AND THE
REMAINS OF THE FRONTAL BOUNDARY SHOULD SERVE AS A FOCUS FOR VERY
ISOLATED SHOWER ACTIVITY.

TEMPERATURES WILL GENERALLY BE NEAR NORMAL FOR TODAY AND TOMORROW
ACROSS THE REGION. HOWEVER...SURGE OF DRIER AND SLIGHTLY COOLER
AIR WILL ADVECT INTO THE REGION MONDAY NIGHT AND LINGER THROUGH
TUESDAY. THIS WEAK COLD AIR ADVECTION WILL PUSH TEMPERATURES
SLIGHTLY BELOW SEASONAL NORMS...WITH OVERNIGHT LOWS DIPPING INTO
THE UPPER 50S ACROSS SOUTHWEST MISSISSIPPI AND FAR INLAND PORTIONS
OF THE FLORIDA PARISHES.


.LONG TERM...

MODEL DIFFERENCES BEGIN TO ARISE HEADING INTO THE LATTER HALF OF
THE WEEK AND THE UPCOMING WEEKEND. THE BIGGEST DIFFERENCE BETWEEN
THE MODELS IS THE SPEED OF A STRONG UPPER LEVEL TROUGH MOVING OUT
OF THE WESTERN THIRD OF THE CONUS AND INTO THE CENTRAL PORTION OF
THE CONUS LATE THIS WEEK. THE GFS IS FASTER WITH THIS FEATURE THAN
EITHER THE CMC OR THE ECMWF. GIVEN RECENT TRENDS OVER THE WEST
COAST...AS ENERGY DIGS INTO CALIFORNIA IT SHOULD BECOME CUT OFF
FROM THE STRONGER UPPER LEVEL FLOW OVER THE PACIFIC NORTHWEST AND
WESTERN CANADA. AS THE LOW CLOSES OFF AND BECOMES INDEPENDENT OF
THE JET STREAM TO THE NORTH IT WILL MEANDER OVER CALIFORNIA AND
THE FOUR CORNERS UNTIL THE NEXT UPPER LEVEL TROUGH DIVES INTO THE
PACIFIC NORTHWEST EARLY NEXT WEEK AND FINALLY KICKS THE SYSTEM TO
THE EAST. OVER THE EASTERN HALF OF THE CONUS...A BROAD UPPER LEVEL
RIDGE SHOULD BEGIN TO FORM ON WEDNESDAY AND BECOME FIRMLY
ENTRENCHED FOR THE WEEKEND. THE GULF SOUTH WILL BE ON THE SOUTHERN
PERIPHERY OF THIS BROAD RIDGE AND THUS WILL BE STUCK FIRMLY IN
DEEP LAYER EASTERLY FLOW.

THIS EASTERLY FLOW WILL LEAD TO A GRADUAL INCREASE IN MOISTURE
ACROSS THE REGION THROUGH THE LATTER PORTION OF THE WEEK.
INITIALLY...THERE WILL CONTINUE TO BE A FAIRLY SHARP MOISTURE
GRADIENT OVER THE AREA...WITH DEEPER MOISTURE GENERALLY CONFINED
TO THE COAST AND OFFSHORE WATERS ON WEDNESDAY. CONDITIONS WILL
BEGIN TO TURN MORE FAVORABLE FOR PRECIPITATION TO DEVELOP OVER THE
AREA ON THURSDAY...AS MID-LEVEL INVERTED TROUGH RIDING AROUND THE
RIDGE TO THE NORTH SLIDES THROUGH THE GULF SOUTH. INCREASED
VORTICITY IN THE MID-LEVELS AND SOME LOW LEVEL SPEED CONVERGENCE
IN THE VICINITY OF THE TROUGH WILL ALLOW FOR HIGHER CHANCES OF
RAINFALL ON THURSDAY. RAIN CHANCES WILL BE GREATEST OVER THE
COASTAL WATERS AND IMMEDIATE COAST...BUT SOME ISOLATED CONVECTION
SHOULD BEGIN TO SPREAD INLAND DURING THE AFTERNOON HOURS.

THE INVERTED TROUGH WILL CONTINUE TO MOVE THROUGH THE GULF OF
MEXICO AND THE FORECAST AREA ON FRIDAY AND SATURDAY...BRINGING
DEEP TROPICAL MOISTURE INTO THE REGION. AMPLE LIFT AND INSTABILITY AS A
RESULT...HAVE PUT CHANCE POPS FOR SCATTERED SHOWERS AND
THUNDERSTORMS IN PLACE FOR ALL OF THE FORECAST AREA BOTH DAYS.
WITH THE INCREASED CLOUD COVER AND CONVECTION IN
PLACE...AFTERNOON TEMPERATURES WILL LIKELY BE SLIGHTLY COOLER
THAN AVERAGE FOR FRIDAY AND SATURDAY...BUT OVERNIGHT LOWS WILL BE
NEAR NORMAL.

&&

.AVIATION...

VFR CONDITIONS ARE FORECAST TO PREVAIL WITH A DRY AIRMASS IN PLACE.
THE EXCEPTION WILL BE MVFR CONDITIONS DUE TO AREAS OF LIGHT FOG /BR/
FOR KMCB AND POSSIBLY KBTR EARLY THIS MORNING...AND POSSIBLY A FEW
ADDITIONAL AIRPORTS LATE TONIGHT/EARLY MONDAY MORNING WHEN SOME
TEMPO IFR COULD OCCUR. ANY ISOLATED SHOWERS ARE EXPECTED TO REMAIN
MOSTLY OFFSHORE/ WELL SOUTH OF THE COASTAL AIRPORTS THROUGH SUNDAY
NIGHT. ISOLATED SHRA/TSRA...ASSOCIATED WITH THE NEXT COLD
FRONT...COULD IMPACT A FEW TERMINALS OR THE VICINITY OF TERMINALS ON
MONDAY...BUT THE PROBABILITY WILL LIKELY REMAIN TOO LOW FOR MENTION
IN THE TAFS WITH THE LATER TAF ISSUANCES TODAY. 22/TD

&&

.MARINE...

A SOMEWHAT TIGHT PRESSURE GRADIENT REMAINS IN PLACE ACROSS THE
COASTAL WATERS RESULTING FROM HIGH PRESSURE OVER THE SOUTHEAST U.S.
AND LOWER PRESSURE NEAR THE STALLED FRONTAL BOUNDARY OVER THE NORTH
GULF OF MEXICO. WITH THE EXCEPTION OF THE HIGHER PLATFORMS...WINDS
HAVE DIMINISHED SLIGHTLY DOWN TO AROUND 15 KNOTS WITH SEAS MOSTLY 5
FEET OR LESS. THIS WILL LEAD TO PERIOD OF LIGHTER WINDS AND LOWER
SEAS FOR THE LAKES...SOUNDS...AND NEAR SHORE WATERS TODAY AND OUTER
COASTAL WATERS BY TONIGHT AND MONDAY.

A FAIRLY STRONG REINFORCING COLD FRONT...BRINGING THE FIRST AUTUMN
EPISODE OF BELOW NORMAL TEMPERATURES AND FAIRLY DRY AIR...WILL PUSH
SOUTH ACROSS THE COASTAL WATERS LATE MONDAY AND MONDAY NIGHT. THIS
IS EXPECTED TO CREATE UNSTABLE NEAR SURFACE CONDITIONS OFFSHORE DUE
TO HIGHER AIR VERSUS WATER TEMPERATURE DIFFERENTIALS. THE MODELS
OFTER TEND TO UNDERESTIMATE THE WINDS IN THESE AUTUMN PATTERNS...SO
HAVE GONE WITH THE HIGHER MAV ADJUSTED WINDS OFFSHORE MONDAY NIGHT
AND EARLY TUESDAY MORNING WHEN A SMALL CRAFT ADVISORY WILL LIKELY BE
REQUIRED FOR AT LEAST THE COASTAL WATERS TO THE EAST OF SOUTHWEST
PASS.

THE PRESSURE GRADIENT WILL REMAIN TIGHT OVER THE NORTH GULF COAST
REGION TUESDAY AND ESPECIALLY ON WEDNESDAY DUE TO HIGH PRESSURE
ASSOCIATED WITH THE COOLER DRY AIRMASS OVER LAND AND THE FRONTAL
BOUNDARY AND LOWER PRESSURE OVER THE GULF. WINDS AND SEAS ARE
EXPECTED TO REMAIN NEAR SMALL CRAFT ADVISORY CRITERIA OVER THE
EASTERN WATERS THROUGH THE DAY ON TUESDAY THEN WINDS EXCEEDING SMALL
CRAFT CRITERIA SHOULD SPREAD INTO ALL COASTAL WATERS AND SOUNDS BY
WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING. THE DURATION OF
STRONGER EAST TO NORTHEAST WINDS WILL ALSO BE LONG ENOUGH TO PUSH
TIDES UP TO AT LEAST ONE FOOT ABOVE NORMAL ALONG THE EAST FACING
SHORELINES THURSDAY INTO FRIDAY MORNING. FOR LONGER RANGE
PLANNERS...WINDS AND SEAS AT THIS POINT LOOK LIKE THEY WILL SUBSIDE
NEXT WEEKEND. 22/TD

&&

.DECISION SUPPORT...

.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  91  69  88  58 /   0  10  20  10
BTR  91  69  88  62 /   0  10  20  10
ASD  90  68  90  61 /  10  10  20  10
MSY  89  73  89  70 /  10  10  20  10
GPT  90  71  91  66 /  10  10  20  10
PQL  89  69  90  63 /  10  10  20  10

&&

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

$$

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