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

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208
FXUS64 KLIX 220045
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
645 PM CST SAT FEB 21 2015

...SOUNDING DISCUSSION...
THE SOUNDING THIS EVENING REPRESENTS A WARM AND MOIST AIRMASS FOR
THIS TIME OF YEAR WITH PW AT 1.22 INCHES. LOW LEVELS FROM THE SFC
TO 700 MB HAVE WARMED 10-15 F FROM 24 HOURS AGO. WINDS ARE
SOUTHWEST FROM THE SFC TO 850 MB THEN BECOME WESTERLY FOR THE REST
OF THE PROFILE ALOFT. PEAK WIND IS 95 KTS AT 195 MB.
KRAUTMANN

&&

.PREV DISCUSSION... /ISSUED 424 PM CST SAT FEB 21 2015/

SYNOPSIS...

THERE HAS BEEN LITTLE CHANGE IN THE OVERALL FORECAST FROM THE
PREVIOUS PACKAGE...AS THE MODELS CONTINUE TO SHOW A VERY UNSETTLED
ZONAL FLOW PATTERN DOMINATING THE GULF SOUTH. A SERIES OF WEAK
UPPER LEVEL VORTICITY MAXIMA EJECTING OUT OF THE FOUR
CORNERS...COMBINED WITH CONTINUED TROUGHING OVER THE GREAT LAKES
SENDING DOWN A SERIES OF REINFORCING FRONTAL BOUNDARIES INTO THE
DEEP SOUTH WILL KEEP A COOL AND WET PATTERN OVER THE REGION FOR
MUCH OF THE FORECAST PERIOD.

SHORT TERM...

TONIGHT AND INTO TOMORROW...ONSHORE FLOW FROM THE GULF OF MEXICO IN
ADVANCE OF A PASSING SHORTWAVE TROUGH AND ASSOCIATED WEAK SURFACE
LOW MOVING THROUGH THE LOWER MISSISSIPPI VALLEY WILL CONTINUE TO
PUMP AND WARM AND MOIST AIRMASS INTO THE REGION. LARGELY OVERCAST
SKIES AND A RISK OF SOME SCATTERED SHOWERS AND A FEW THUNDERSTORMS
WILL BE FOUND OVER MOST OF THE FORECAST AREA TONIGHT. ANY
THUNDERSTORMS WILL GENERALLY BE OVER FAR NORTHERN ZONES WHERE THE
THERMODYNAMIC PROFILES ARE MORE FAVORABLE FOR SOME DEEPER
CONVECTION TO FORM. TEMPERATURES WILL BE WELL ABOVE NORMAL...WITH
LOWS IN THE UPPER 50S OVER MOST OF THE AREA. THE WIND FIELD IS
EXPECTED TO WEAKEN LATER TONIGHT...AND THERE COULD BE SOME AREAS
OF FOG FORMING LATE TONIGHT INTO EARLY TOMORROW MORNING. DENSE FOG
IS NOT EXPECTED AS OVERALL MIXING IN THE BOUNDARY LAYER SHOULD
STILL BE FAIRLY STRONG.

THE SLOW MOVING AREA OF LOW PRESSURE WILL MOVE INTO GEORGIA BY
TOMORROW AFTERNOON. AS THE LOW PULLS TO THE EAST...A COLD FRONT
WILL DRIFT SOUTH ACROSS THE FORECAST AREA THROUGH THE DAY. IN
ADVANCE OF THIS FRONT...SOME MARGINAL CAPE COULD ALLOW FOR
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS TO DEVELOP FROM THE
LATE MORNING INTO THE EARLY EVENING HOURS. ANY CONVECTION WILL
TEND TO BE LOW TOPPED AS A WEAK MID-LEVEL CAP LINGERS INTO THE
AFTERNOON HOURS. NO SEVERE THUNDERSTORM ACTIVITY IS
EXPECTED...WITH A BRIEF HEAVY DOWNPOURS AND LIGHTNING STRIKES
EXPECTED TO BE THE PRIMARY THREAT FROM ANY THUNDERSTORM ACTIVITY.
TEMPERATURES WILL REMAIN WARM IN ADVANCE OF THE FRONT...WITH HIGHS
RISING BACK INTO THE LOWER 70S ACROSS MOST OF THE FORECAST AREA.

THE FRONT WILL FINALLY PUSH SOUTH AND EAST OF THE FORECAST AREA
LATE SUNDAY NIGHT INTO EARLY MONDAY. AS THIS OCCURS...ANOTHER WEAK
VORT LOBE WILL SLIDE THROUGH THE REGION. INCREASED UPPER LEVEL
OMEGA...COMBINED WITH A WARMER AND MORE MOIST AIRMASS JUST OFF THE
SURFACE RIDING UP OVER A COOLER AND MORE STABLE AIRMASS AT THE
SURFACE WILL KEEP EXTENSIVE CLOUD COVER AND A CHANCE OF RAIN OVER
THE AREA THROUGH THE DAY MONDAY AND INTO MONDAY NIGHT.
TEMPERATURES WILL BE SIGNIFICANTLY COLDER AS LOW LEVEL COLD AIR
ADVECTION CONTINUES AND THE CLOUDS REDUCE SOLAR INSOLATION LEVELS
DRAMATICALLY. HIGHS WILL BE A GOOD 30 DEGREES COLDER WITH READINGS
IN THE 40S OVER MOST OF THE AREA. THE OVERRUNNING PRECIPITATION
EVENT WILL CONTINUE INTO MONDAY NIGHT AND EARLY TUESDAY. AS
OVERNIGHT LOWS COOL INTO THE 30S AND POSSIBLY UPPER
20S...CONDITIONS WILL TURN FAVORABLE FOR SOME LIGHT FREEZING RAIN
TO IMPACT THE SOUTHWEST MISSISSIPPI COUNTIES AND NORTHERN PORTIONS
OF THE NORTHSHORE AND METRO BATON ROUGE. MODEL SOUNDINGS SHOW A
FULLY SATURATED AIRMASS COOLING TO BELOW FREEZING OVER THE
NORTHERN THIRD OF THE FORECAST AREA AS WEAK COLD AIR ADVECTION
CONTINUES ON THE BACK OF A NORTHEAST WIND IN THE LOW LEVELS.
ABOVE THIS SHALLOW COLD LAYER AT THE SURFACE...WESTERLY FLOW WILL
RESULT IN A MUCH WARMER MID-LEVEL AIRMASS WITH STRONG WARMING OF
AROUND 8 DEGREES CELSIUS NOTED ALONG THE INVERSION. GIVEN
THIS...EXPECT TO RAIN FALLING THROUGH THE ATMOSPHERIC COLUMN UNTIL
IT REACHES THE BELOW FREEZING SURFACE. THE FREEZING RAIN LINE
GENERALLY LOOKS TO EXTEND FROM MARINGOUIN TO BAKER TO GREENSBURG
TO POPLARVILLE AND POINTS NORTHWARD AT THIS TIME. ANY ICE
ACCUMULATIONS WILL BE LIGHT...WITH A TENTH OF AN INCH OR ICE OR
LESS EXPECTED BY MID- MORNING ON TUESDAY. TEMPERATURES WILL RISE
ABOVE FREEZING BY LATE MORNING TUESDAY...AND THE ICE SHOULD
QUICKLY MELT AFTER THAT. TEMPERATURES WILL REMAIN COLD ON
TUESDAY...WITH HIGHS RISING ONCE AGAIN ONLY CLIMBING INTO THE 40S.

LONG TERM...

THE MOST POTENT OF THE VORTICITY MAXIMA KICKING OUT OF THE
SOUTHWEST CONUS WILL APPROACH THE AREA TUESDAY NIGHT AND PASS
THROUGH THE REGION DURING THE DAY ON WEDNESDAY. AS THIS FAIRLY
VIGOROUS TROUGH APPROACHES...STRONG POSITIVE VORTICITY ADVECTION
WILL LEAD TO INCREASING MID AND UPPER LEVEL OMEGA ACROSS THE AREA.
IN THE LOW LEVELS...JET DYNAMICS WILL BE FAVORABLE FOR A SURFACE
LOW TO FORM IN A REGION OF STRONG BAROCLINICITY OVER THE WESTERN
GULF. A GULF LOW WILL DEVELOP AND QUICKLY TRACK TO THE EAST
THROUGH THE NORTHERN GULF OF MEXICO ON WEDNESDAY. WARM FRONTAL
PROCESSES IN ADVANCE OF THIS LOW WILL INCREASE THE LOW LEVEL
ISENTROPIC FORCING...AND EXPECT TO SEE A FAIRLY BROAD SHIELD OF
LIGHT TO MODERATE RAIN IMPACT THE AREA TUESDAY NIGHT AND
WEDNESDAY. FORTUNATELY...THESE WARM FRONTAL PROCESSES WILL ALLOW
TEMPERATURES TO REMAIN ABOVE FREEZING TUESDAY NIGHT INTO EARLY
WEDNESDAY. HIGHS WILL REMAIN COOL ON WEDNESDAY...WITH READINGS IN
THE UPPER 40S AND LOWER 50S DUE TO THE CLOUD
COVER...RAINFALL...AND A NORTHEAST FLOW INTENSIFYING IN THE WAKE
OF THE PASSING LOW DURING THE AFTERNOON HOURS.

AS THE LOW PULLS TO THE EAST WEDNESDAY NIGHT...SOME DRIER AIR AND
INCREASED SUBSIDENCE IN THE WAKE OF THE TROUGH WILL ALLOW FOR A
RESPITE FROM THE RAINFALL. SOME ISOLATED SHOWERS WILL LINGER OVER
THE EASTERN ZONES WEDNESDAY EVENING...BUT EXPECT DRY WEATHER TO BE
IN PLACE FOR THE ENTIRE AREA FROM LATE WEDNESDAY NIGHT THROUGH
THURSDAY NIGHT. SKIES WILL CLEAR PARTIALLY...WITH PARTLY CLOUDY
SKIES EXPECTED ON THURSDAY...AND TEMPERATURES WILL BE WARMER ON
THURSDAY DUE TO THE INCREASED SOLAR INSOLATION. HIGHS WILL REMAIN
BELOW NORMAL...BUT WILL WARM INTO THE MIDDLE 50S BY THE AFTERNOON.
TEMPERATURES WILL BE COOL BOTH WEDNESDAY NIGHT AND THURSDAY NIGHT
INTO THE 30S AND LOWER 40S ACROSS THE AREA.

THE BRIEF BREAK IN THE RAINFALL WILL BE SHORT-LIVED...AS ANOTHER
POTENT UPPER LEVEL TROUGH BEGINS TO EJECT OUT OF THE FOUR CORNERS
ON FRIDAY. INCREASING POSITIVE VORTICITY ADVECTION WILL PRODUCE A
BROAD REGION OF LIFT OVER THE GULF SOUTH. AT THE SAME...ANOTHER
GULF LOW WILL DEVELOP OVER THE WESTERN GULF AND QUICKLY HEAD
TOWARD THE FORECAST AREA. EXPECT TO SEE INCREASING CLOUD COVER AND
RAIN CHANCES THROUGH THE DAY ON FRIDAY AND INTO FRIDAY NIGHT.
THERE WILL BE LITTLE CHANGE IN THE TEMPERATURE REGIME...WITH HIGHS
ONCE AGAIN CLIMBING INTO THE 50S DURING THE AFTERNOON. THE CLOUD
COVER OVER THE REGION...COMBINED WITH ANOTHER ROUND OF WARM
FRONTAL PROCESSES SHOULD KEEP TEMPERATURES WARMER FRIDAY NIGHT.
LOWS WILL ONLY DROP ABOUT 10 DEGREES FROM THE HIGHS...WITH
READINGS IN THE 40S ACROSS THE REGION. CONDITIONS WILL BRIEFLY
IMPROVE IN THE WAKE OF THE NEXT TROUGH ON SATURDAY...WITH
PARTIALLY CLEARING SKIES AND LOWER RAIN CHANCES. TEMPERATURES WILL
REMAIN BELOW AVERAGE IN THE 50S.

AVIATION...

VFR CEILINGS BASED AROUND 040-050 WILL LOWER WITH RAINFALL ON-SETTING
LATER THIS EVENING AND OVERNIGHT...GENERALLY IN MVFR RANGES.
CONVECTION LIKELY TO DEVELOP AFTER SUNSET. TSRA OCCURRING FARTHER
NORTH ALONG I-20 CORRIDOR MAY REMAIN NORTH OF TERMINALS...THOUGH
ISOLATED TSRA CAN NOT BE RULED OUT FOR KMCB AND KBTR LATER TONIGHT.
24/RR

MARINE...

A LONG FETCH OF 20 TO 30 KNOT WINDS ASSOCIATED WITH A STRONG
PRESSURE GRADIENT BETWEEN A RIDGE OVER THE SOUTHEAST AND A LOW IN
THE ARKLATEX HAS ALLOWED FOR A LONG FETCH SWELL TRAIN OF 2 TO
3 FEET TO FEED INTO THE GULF COASTAL WATERS. AS A RESULT...SEAS OF
9 TO 12 FEET HAVE OCCURRED OVER THE OPEN GULF WATERS TODAY. AS THE
GRADIENT AND OVERALL WIND FIELD DECREASES TONIGHT TO BELOW 15
KNOTS...SEAS WILL REMAIN ELEVATED AND HAVE KEPT UP SMALL CRAFT
ADVISORIES FOR EXPECTED 5 TO 8 FEET SEAS OVER THE OUTER WATERS.
THERE WILL BE A BRIEF PERIOD TOMORROW...WHERE WINDS AND SEAS WILL
FINALLY START TO MATCH UP...AND NO SMALL CRAFT ADVISORY CONDITIONS
ARE EXPECTED. HOWEVER...A STRONG COLD FRONT WILL SWEEP THROUGH
TOMORROW NIGHT...RESULTING IN STRONG OFFSHORE FLOW OF 20 TO 25
KNOTS AND A RETURN TO ROUGH 5 TO 7 FEET IN SEAS IN THE OPEN GULF
WATERS THROUGH MONDAY. WINDS WILL EASE BACK BELOW ADVISORY LEVELS
MONDAY NIGHT AND REMAIN AT 10 TO 15 KNOTS FROM THE EAST-NORTHEAST
THROUGH TUESDAY NIGHT. SEAS WILL FALL BACK TO 2 TO 3 FEET IN THE
SOUNDS AND LAKES...AND 3 TO 5 FEET IN THE OPEN GULF WATERS.
HOWEVER...ANOTHER GULF LOW WILL BRING SMALL CRAFT CONDITIONS BACK
TO COASTAL WATERS WEDNESDAY INTO WEDNESDAY NIGHT.

DECISION SUPPORT...

DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
             ASSESSING WINTER WEATHER POTENTIAL FOR MON NIGHT.

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  70  58  65  36 /  30  80  50  60
BTR  74  60  70  40 /  30  70  40  50
ASD  72  58  73  44 /  30  40  30  40
MSY  74  59  72  46 /  20  30  30  40
GPT  69  57  70  44 /  20  30  30  40
PQL  70  58  72  44 /  20  30  30  40

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 6 AM SUNDAY 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 PORT FOURCHON TO LOWER ATCHAFALAYA RIVER FROM
     20 TO 60 NM...COASTAL WATERS FROM STAKE ISLAND LA TO THE
     SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60
     NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON FROM 20 TO 60 NM...AND
     COASTAL WATERS FROM THE SOUTHWEST PASS OF THE MISSISSIPPI
     RIVER TO PORT FOURCHON OUT 20 NM.

     SMALL CRAFT ADVISORY UNTIL MIDNIGHT SUNDAY FOR THE FOLLOWING
     ZONES: BRETON SOUND...CHANDELEUR SOUND...COASTAL WATERS
     FROM PASCAGOULA MS TO STAKE ISLAND LA OUT 20 NM...AND
     COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA
     RIVER OUT 20 NM.

MS...NONE.
GM...SMALL CRAFT ADVISORY UNTIL MIDNIGHT SUNDAY FOR THE FOLLOWING
     ZONES: BRETON SOUND...CHANDELEUR SOUND...COASTAL WATERS
     FROM PASCAGOULA MS TO STAKE ISLAND LA OUT 20 NM...AND
     COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA
     RIVER OUT 20 NM.

     SMALL CRAFT ADVISORY UNTIL 6 AM SUNDAY 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 PORT FOURCHON TO LOWER ATCHAFALAYA RIVER FROM
     20 TO 60 NM...COASTAL WATERS FROM STAKE ISLAND LA TO THE
     SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60
     NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON FROM 20 TO 60 NM...AND
     COASTAL WATERS FROM THE SOUTHWEST PASS OF THE MISSISSIPPI
     RIVER TO PORT FOURCHON OUT 20 NM.

&&

$$







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