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

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632
FXUS64 KLIX 201343
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
743 AM CST FRI FEB 20 2015

...SOUNDING DISCUSSION...
THE SOUNDING THIS MORNING HAS A 12 F SFC TEMPERATURE INVERSION.
SOUTH WINDS ARE NEAR THE SFC WITH WESTERLY FLOW ALOFT BEGINNING
ABOVE THE INVERSION AT 036 FT. THE JET MAX IS 135 KTS AT 200 MB.
THERE IS ALREADY SLIGHTLY MORE MOISTURE IN THE PROFILE THAN
YESTERDAY WITH PW AT .43 INCHES.

KRAUTMANN

&&

.PREV DISCUSSION... /ISSUED 345 AM CST FRI FEB 20 2015/

SHORT TERM...
TEMPERATURES WILL BEGIN TO MODIFYING TODAY AS UPPER LEVEL TROUGH
OVER THE EASTERN HALF OF THE COUNTRY LIFTS NORTHEAST AND 500MB
HEIGHTS INCREASE LOCALLY. MOST LOCATIONS SHOULD SEE ABOUT A 10
DEGREE INCREASE FROM YSTRDY. MOISTURE LEVELS WILL START INCREASING
AS WELL WITH THE SURFACE RIDGE TO THE NORTH SLIDING EAST AND
ALLOWING SOUTHEASTERLY FLOW TO BECOME BETTER ESTABLISHED. COULD SEE
A 20 DEGREE JUMP IN DEWPOINTS FROM THIS MORNING TO LATE AFTERNOON
WITH A GRADIENT OF HIGHER MOISTURE FROM EAST TO WEST. MODEL
SOUNDINGS SHOW PRECIP WATER VALUES DOUBLING FROM MORNING TO
AFTERNOON. A FEW SHOWERS COULD BEGIN TO DEVELOP TODAY ACROSS THE
AREA BUT COVERAGE WILL PROBABLY BE QUITE SPARSE. THE BEST CHANCE TO
SEE ANY RAIN WILL BE ALONG THE LA COAST WEST OF THE MISSISSIPPI
RIVER. LOOKS LESS POSSIBLE EAST OF NEW ORLEANS...SO HAVE DROPPED
POPS FROM THE GRIDS THERE AND ONLY 20PCT FOR THE REST OF THE CWA.

A LEESIDE TROUGH OF LOW PRESSURE CURRENTLY IN PLACE OVER THE TEXAS
PANHANDLE WILL BEGIN MOVING EAST IN RESPONSE TO AN UPPER LEVEL
TROUGH DIGGING OUT OF CANADA AND INTO THE CENTRAL PLAINS. THIS LOW
WILL TRACK ACROSS OKLAHOMA AND ARKANSAS TONIGHT. GULF MOISTURE WILL
BE DRAWN INTO THIS LOW WHICH WILL ENHANCE SHOWER DEVELOPMENT OVER
THE CWA. GFS SEEMS TO BE TOO BULLISH AND ECWMF TOO CONSERVATIVE...SO
FORECAST IS A BLEND OF THE TWO. THIS TREND WILL CONTINUE INTO
SATURDAY WITH THE SFC LOW RACING NORTHEAST AND A COLD FRONT MOVES
SOUTHWARD ACROSS TEXAS AND LOUISIANA IN ITS WAKE. HIGHER RAIN
CHANCES SHOULD STILL BE IN THE NORTHERN HALF OF THE FORECAST AREA.
DO HAVE ISOLATED THUNDERSTORMS IN THE FCST FOR SATURDAY AS THERE
WILL BE JUST ENOUGH INSTABILITY FOR A FEW RUMBLES OF THUNDER.

THE FRONTAL BOUNDARY WILL FINALLY MAKE ITS WAY INTO THE CWA SATURDAY
NIGHT. IT WILL BE THE FOCUS FOR SHOWERS AND A FEW THUNDERSTORMS AND
POPS WILL CONTINUE TO RISE NORTH OF INTERSTATE 12. HAVE INCREASED
THEM TO 60-80% FOR THIS TIMEFRAME. THE FRONT WILL SLOWLY CONTINUE
SOUTHWARD ACROSS THE FORECAST AREA SUNDAY. THIS TIMING IS SLIGHTLY
FASTER THAN PREVIOUS MODEL RUNS SO HAVE BROUGHT IN COOLER AIR
QUICKER FOR MAX TEMPS SUNDAY FROM THE PREVIOUS FORECAST. THERE WILL
BE QUITE A LARGE GRADIENT IN TEMPS ACROSS THE AREA AND THUS COULD BE
A LARGER THAN NORMAL ERROR IN FCST HIGHS IF THE COLD AIR MOVES IN
FASTER OR SLOWER THAN CURRENT FORECAST.

LONG TERM...
CHANCE CATEGORY POPS WILL CONTINUE ON MONDAY AS THE AREA REMAINS
UNDER AN UPPER LEVEL SHEAR AXIS BETWEEN TROUGH TO THE NORTH AND
RIDGE TO THE SOUTH. MEANWHILE...COLD AIR ADVECTION WILL BRING TEMPS
DOWN CONSIDERABLY. HIGHS WILL STRUGGLE TO REACH LOWER TO UPPER 40S
ACROSS THE CWA. RAIN CHANCES SHOULD BE FOCUSED ALONG THE COAST WITH
SOME INLAND INTRUSION. HOW FAR IN BECOMES CRITICAL IN THE OVERNIGHT
PERIOD AS TEMPS BEGIN TO FALL. THERE COULD BE A WINDOW OF
OPPORTUNITY FOR FREEZING RAIN ALONG THE MISSISSIPPI/LOUISIANA BORDER
IN THE CWA MONDAY NIGHT BUT VERY DEPENDENT ON THE AVAILABILITY OF
MOISTURE AND IF TEMPS ARE COLD ENOUGH AT THAT TIME. HOLDING OFF ON
MENTION OF ZR- FOR NOW AS GFS SHOWS COLDER AND NO PRECIP WHILE ECMWF
SHOWS RAIN BUT WARMER.

MODEL DISCONTINUITY GETS EVEN WORSE MIDWEEK. THE GFS SHOWS A SFC LOW
DEVELOPING ALONG THE CENTRAL GULF COAST WEDNESDAY AND RACING
NORTHEAST BEFORE ANOTHER UPPER LEVEL TROUGH DIGS ACROSS THE ROCKIES
AND SWINGS THROUGH OVER THE WEEKEND. THE ECMWF IS ABOUT 30 HOURS
SLOWER ON THE GULF LOW DEVELOPMENT AND TROUGH SWINGING THROUGH. SO
FOR NOW HAVE JUST KEPT THE FORECAST POPS ON THE LOW SIDE THE REST OF
THE WEEK.

MEFFER

AVIATION...
VFR CONDITIONS AND CLEAR SKIES WILL GRADUALLY BECOME MVFR DUE TO
CIGS THIS AFTERNOON AND EVENING. ISOLATED TO LOCALLY SCATTERED SHRA
MAY DEVELOP DURING THE MID TO LATE AFTERNOON HOURS THEN INCREASE IN
COVERAGE TONIGHT. IFR CIGS WILL BE POSSIBLE AT TIMES LATE TONIGHT
AND EARLY SATURDAY MORNING AT SOME OF THE TAF SITES. 11

MARINE...
ONSHORE FLOW WAS DEVELOPING ACROSS THE COASTAL WATERS EARLY THIS
MORNING AS A RIDGE OF HIGH PRESSURE CONTINUED TO SHIFT OFF TO THE
EAST. THIS FLOW WILL INCREASE IN MAGNITUDE TODAY AS A TIGHT
PRESSURE GRADIENT DEVELOPS ACROSS THE COASTAL WATERS IN RESPONSE TO
DEVELOPING LOW PRESSURE IN THE SOUTHERN PLAINS IN CONJUNCTION WITH
HIGH PRESSURE OVER THE SOUTHEAST CONUS. ONSHORE FLOW OF 20 TO 30
KNOTS IS EXPECTED FROM LATE TODAY THROUGH SATURDAY. SMALL CRAFT
ADVISORIES ARE IN PLACE FOR THIS TIME PERIOD. WINDS WILL DIMINISH ON
SUNDAY. A COLD FRONT WILL PUSH ACROSS THE COASTAL WATERS LATE SUNDAY
AND SUNDAY NIGHT RESULTING IN THE DEVELOPMENT OF MODERATE TO STRONG
OFFSHORE FLOW SUNDAY NIGHT INTO MONDAY. 11

DECISION SUPPORT...
DSS CODE...BLUE.
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  58  55  70  56 /  20  50  50  80
BTR  62  57  74  58 /  20  30  50  80
ASD  60  55  74  56 /  10  30  40  60
MSY  62  58  75  60 /  20  30  40  40
GPT  57  55  68  57 /  10  20  30  60
PQL  57  53  69  58 /  10  20  30  60

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
GM...SMALL CRAFT ADVISORY FROM NOON FRIDAY TO 3 AM SUNDAY FOR THE
     FOLLOWING ZONES: BRETON SOUND...CHANDELEUR SOUND...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 PASCAGOULA MS TO STAKE ISLAND LA OUT 20
     NM...COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA
     RIVER FROM 20 TO 60 NM...COASTAL WATERS FROM PORT FOURCHON
     TO LOWER ATCHAFALAYA RIVER OUT 20 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 FROM 6 PM FRIDAY TO 6 PM SATURDAY FOR THE
     FOLLOWING ZONES: AND MISSISSIPPI SOUND.

MS...NONE.
GM...SMALL CRAFT ADVISORY FROM 6 PM FRIDAY TO 6 PM SATURDAY FOR THE
     FOLLOWING ZONES: AND MISSISSIPPI SOUND.

     SMALL CRAFT ADVISORY FROM NOON FRIDAY TO 3 AM SUNDAY FOR THE
     FOLLOWING ZONES: BRETON SOUND...CHANDELEUR SOUND...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 PASCAGOULA MS TO STAKE ISLAND LA OUT 20
     NM...COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA
     RIVER FROM 20 TO 60 NM...COASTAL WATERS FROM PORT FOURCHON
     TO LOWER ATCHAFALAYA RIVER OUT 20 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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