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

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563
FXUS64 KLIX 141629
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1129 AM CDT MON APR 14 2014

.UPDATE...
GFS AND MET GUIDANCE ARE BOTH MAINTAINING NORTH WINDS AT ABOVE 30
KNOTS AT LAKEFRONT FROM 06Z TO 12Z. IN ADDITION...ASTRONOMICAL
HIGH TIDE WILL OCCUR THIS EVENING AT NEW CANAL AND OTHER POINTS
ALONG THE SOUTH SHORE. THIS DURATION WILL ALLOW WINDS TO PUSH
WATER ON ROADS OUTSIDE THE PROTECTION LEVEE AT TIMES.

&&

.PREV DISCUSSION... /ISSUED 853 AM CDT MON APR 14 2014/

UPDATE...
..SOUNDING DISCUSSION...

NO PROBLEMS WITH THE FLIGHT THIS MORNING. THE SOUNDING SHOWS THE
HUGE INCREASE IN MOISTURE OVER THE AREA AS PW VALUES ARE UP TO
1.63 INCHES ALTHOUGH THERE IS A DECENT AMOUNT OF DRY AIR IN THE
MID-LEVELS. SOUTHERLY WINDS AT THE SURFACE QUICKLY SHIFT TO THE
WEST...PROVIDING A GOOD AMOUNT OF DIRECTIONAL SHEAR IN THE LOWER
LEVELS. IN ADDITION...0-3KM SHEAR VALUES OF 30-35 KNOTS ARE SHOWN.
FREEZING LEVEL HEIGHT JUST ABOVE 13K FEET BUT WET BULB ZERO
HEIGHTS ARE LOWER AROUND 11K. AS THE MORNING AND AFTERNOON
PROGRESS...DESTABILIZATION WILL OCCUR AS TEMPERATURES REACH TO
NEAR 80 ACROSS MOST OF THE AREA. THIS WILL ALLOW FOR A DECENT
AMOUNT OF MLCAPE WITH MODERATE LAPSE RATES. THE SOUNDING HODOGRAPH
ALSO SHOWS A FAIRLY IMPRESSIVE CURVED SHAPE WITH HELICITY VALUES
BETWEEN 350-400 M2/S2 AT THE PRESENT TIME...ALTHOUGH MODEL
SOUNDINGS SHOW THIS NUMBER DROPPING OFF CONSIDERABLY BEFORE THE
STRONGER STORMS ARE EXPECTED TO DEVELOP.

ALL OF THAT SAID...STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE
THROUGHOUT THE DAY TODAY...BEGINNING LATER ON THIS AFTERNOON.
STRONG STRAIGHT LINE WINDS AND DAMAGING HAIL ARE LIKELY TO BE THE
MAIN IMPACTS. SEE BELOW DISCUSSION FOR MORE DETAILS ON THE EXPECTED
IMPACTS TODAY.

98/SO

PREV DISCUSSION... /ISSUED 545 AM CDT MON APR 14 2014/

.STRONG TO SEVERE THUNDERSTORMS AND VERY HEAVY RAINFALL POSSIBLE
TODAY AND EARLY TONIGHT...

SYNOPSIS...

COLD FRONT AT 3 AM EXTENDED FROM ST. LOUIS TO TEXARKANA TO THE
BIG BEND OF TEXAS. A PRE-FRONTAL BAND OF CONVECTION HAS SAGGED
SOUTH TO INTERSTATE 20. ANOTHER BAND OF CONVECTION HAS BEEN
ASSOCIATED WITH THE COLD FRONT...BUT HAS BECOME DRIVEN BY A COLD
POOL ON THE NORTH END AND HAS CAUGHT UP TO THE PREFRONTAL
CONVECTION. IT APPEARS THAT ALL CONVECTION WILL REMAIN NORTH AND
WEST OF THE AREA THROUGH SUNRISE...ALTHOUGH PERHAPS JUST BARELY.
SOUTHEAST WINDS AT 10 TO 20 MPH ARE HOLDING TEMPERATURES UP IN THE
LOWER 70S THIS MORNING WITH DEW POINTS IN THE UPPER 60S.

SHORT TERM...

THROUGH TUESDAY NIGHT...

INITIAL SHORTWAVE TROUGH AND ASSOCIATED STRONG COLD FRONT AND
OUTFLOW BOUNDARIES HAVE BEEN PUSHING INTO MID/LOWER MISSISSIPPI
VALLEY...AND THIS HAS BEEN THE FOCUS FOR STRONG THUNDERSTORMS AND
TORRENTIAL RAINFALL ACROSS PORTIONS OF THE ARK-LA-MISS AREA THE LAST
SEVERAL HOURS. THIS HAS GENERATED A COLD POOL AND MERGED BOUNDARIES
OVER CENTRAL MISSISSIPPI WHERE FLASH FLOOD WARNINGS HAVE BEEN ISSUED
DUE TO REPEAT THUNDERSTORMS AND EXTREMELY EFFICIENT RAINFALL
PRODUCTION. OUTFLOW WILL LIKELY CAUSE SHOWERS AND THUNDERSTORMS TO
DEVELOP SOUTH ACROSS SOUTHWEST AND SOUTH CENTRAL MISSISSIPPI EARLY
THIS MORNING...POSSIBLY CROSSING OVER INTO THE ADJACENT UPPER
SOUTHEAST LOUISIANA PARISHES DURING THE MORNING. THERE SHOULD BE
A LULL PERIOD AS FAR AS SUPPORT FOR SEVERE THUNDERSTORMS AND
PERSISTENT HEAVY RAINFALL AS THE MORNING PROGRESSES AND ACTIVITY
MOVES INTO THE FORECAST AREA...HOWEVER AN ISOLATED STRONG TO SEVERE
STORM CANNOT BE RULED OUT ACROSS THE FAR NORTHERN AREAS.

THE FIRST SHORTWAVE WILL LIFT AWAY FROM THE AREA BY LATE MORNING. A
STRONGER LONGWAVE TROUGH WILL DEVELOP AND MOVE ACROSS THE PLAINS/MS
VALLEY TODAY AND TONIGHT WITH AN ASSOCIATED COLD FRONT MOVING
THROUGH SOUTHEAST LOUISIANA AND SOUTHERN MISSISSIPPI LATE THIS
AFTERNOON AND EVENING. PWS OF 1.6-1.9 INCHES WILL POOL AHEAD OF THE
FRONT WHICH WILL BE FROM NEAR TWO STANDARD DEVIATIONS TO THE 99TH
PERCENTILE OF CLIMATOLOGY FOR MID APRIL. INSTABILITY WILL BE RATHER
IMPRESSIVE WITH SURFACE BASED CAPE 2000 TO 3000 J/KG...MEAN LAYER
CAPE OF 1500-2000 J/KG AND LIS OF  -4 TO -8 FROM AROUND MIDDAY
THROUGH AT LEAST MID AFTERNOON. SHEAR PROFILES ARE NOT IDEAL FOR
TORNADOES...BUT STILL ADEQUATE TO SUPPORT A BRIEF WINDOW FOR
SUPERCELLS BEFORE CONVECTION BECOMES MOSTLY LINEAR. EVEN AFTER
THUNDERSTORMS BECOME LINEAR...THERE COULD STILL BE THE POTENTIAL FOR
A FEW STORMS EMBEDDED IN THE SQUALL LINE TO ROTATE AND PRODUCE A
BRIEF TORNADO. OTHERWISE...THE MAIN CONCERNS WILL BE FOR STRONG TO
DAMAGING WINDS ALONG BOWING SEGMENTS...FREQUENT LIGHTNING...AND
POTENTIAL FLASH FLOODING FROM ANY SLOW MOVING BANDS OF THUNDERSTORMS
WITH TORRENTIAL RAINFALL.

HAVE ISSUED A FLASH FLOOD WATCH THIS AFTERNOON AND EVENING FOR AREAS
SOUTH OF THE TIDAL LAKES...ST. TAMMANY PARISH...AND THE MISSISSIPPI
GULF COAST WHERE THE COMBINATION OF THE BEST INITIALIZED ECMWF AND
THE SUITE OF MESOSCALE BASED MODELS ARE SHOWING THE HEAVIEST
RAINFALL DURING PEAK HEATING AND AHEAD OF THE COLD FRONT THIS
AFTERNOON AND EVENING. JUST BASED OFF THE SYNOPTIC PATTERN AND ECMWF
QPF...MOST AREAS SHOULD EXPERIENCE AT LEAST 1 TO 3 INCHES. A MAJOR
CONCERN OF PROPAGATION VECTORS COULD BE EXACTLY OPPOSED TO THE MEAN
STEERING CURRENTS WHICH COULD RESULT IN BACK-BUILDING OR
REGENERATIVE THUNDERSTORMS ALONG LINE SEGMENTS. THIS SUPPORTS SOME
OF THE WRF MODELS THAT INDICATE AS MUCH AS 3 TO 6 INCHES OF RAIN
OVER SOME AREAS FROM SOUTH OF LAKE PONTCHARTRAIN TO NEAR OR JUST
OFFSHORE FROM THE MISSISSIPPI GULF COAST.

OTHER BIG CONCERN WILL BE STRONG WINDS DEVELOPING BEHIND THE COLD
FRONT. NUMEROUS CONSECUTIVE RUNS OF THE MAV MOS FOR KNEW/LAKEFRONT
AIRPORT HAVE INDICATED AROUND 40 KNOTS OR GREATER DURING THE PERIOD
FROM 1 AM TO 7 AM TONIGHT/EARLY TUESDAY MORNING. MOST OF THE MODELS
INDICATE AT LEAST 35 KNOTS AT THE 925 MB LEVEL DEVELOPING ACROSS
MUCH OF THE COASTAL AREAS DURING THIS TIME FRAME...AND THERE WILL
LIKELY BE SUFFICIENT SUBSIDENCE TO BRING THESE WINDS DOWN TO THE
SURFACE AT LEAST IN GUSTS. AM ANTICIPATING NORTH WINDS WILL EASILY
BE IN THE 25 TO 35 MPH RANGE OVER MOST AREAS JUST INLAND FROM THE
SOUTH SHORE OF THE TIDAL LAKES...AND NEAR THE EXTREME SOUTHEAST
LOUISIANA COAST. IT IS POSSIBLE AS INDICATED IN THE MOS GUIDANCE
THAT THE IMMEDIATE LAKEFRONT OF THE SOUTHSHORE COULD BE IN HIGH WIND
WARNING CRITERIA OF 40 TO 45 MPH FOR A FEW HOURS. HAVE DECIDED NOT
TO GO WITH A HIGH WIND WARNING OR WATCH AT THIS TIME...BUT HAVE
ISSUED A STRONGLY WORDED WIND ADVISORY ADDRESSING THE POTENTIAL FOR
STRONGER WINDS DURING THE LATE NIGHT AND EARLY TUESDAY MORNING
HOURS. AS IS OFTEN THE CASE IN SUCH STRONG NORTHERLY WINDS...LARGE
BATTERING WAVES ON THE SOUTH SHORE OF LAKE PONTCHARTRAIN COULD CAUSE
MINOR FLOODING OF LOW LYING AREAS OUTSIDE THE HURRICANE PROTECTION
LEVEE SYSTEM...LIKE ON THE LOW LYING SECTIONS OF LAKESHORE DRIVE IN
NEW ORLEANS. THIS HAS ALSO BEEN MENTIONED IN THE WIND ADVISORY
PRODUCT.

AFTER A WARMER THAN NORMAL SPELL...AN UNSEASONABLY COLD AND MUCH
DRIER AIRMASS WILL TAKE HOLD TUESDAY INTO TUESDAY NIGHT...AND
TEMPERATURES HAVE TRENDED LOWER TUESDAY NIGHT WHEN A BRIEF LIGHT
FREEZE COULD OCCUR IN SOME OF THE COLDER NORTHERN LOCATIONS.

22/TD

LONG TERM...

WEDNESDAY THROUGH THE END OF THE FORECAST.

GUIDANCE CONTINUES TO STRUGGLE SOMEWHAT WITH THE EXTENDED
SCENARIO...BUT HAS COME INTO A LITTLE BETTER AGREEMENT FOR THE END
OF THE WEEK. ECMWF SOLUTION NOW AT LEAST HAS A SYSTEM AFFECTING THE
AREA THURSDAY AND FRIDAY...BUT DRIES EVERYTHING OUT OVER THE
WEEKEND. HAVE BUMPED UP POPS ON THURSDAY AND FRIDAY...NOW CLOSER TO
WHAT GFS HAS BEEN INDICATING. WILL HOLD MINIMAL MENTION OF
PRECIPITATION IN THE FORECAST OVER THE WEEKEND IN RECOGNITION OF THE
POTENTIAL FOR A WEAK FRONT TO WASH OUT ALONG THE COAST.

TEMPERATURES WILL START OUT UNSEASONABLY COLD ON WEDNESDAY MORNING.
AWAY FROM MARINE INFLUENCES...TEMPERATURES WILL FALL INTO THE 30S
ACROSS MUCH OF THE AREA WEDNESDAY MORNING. THIS IS LIKELY TO BE IN
RECORD TERRITORY FOR MANY SITES. WILL NOT GO QUITE AS COLD AS SOME
OF THE MOS GUIDANCE IS SHOWING BUT THIS WILL NEED TO BE MONITORED
FOR THE POTENTIAL OF A LIGHT FREEZE OVER THE NEXT 36 HOURS AS IT
COULD HAVE AN AGRICULTURAL IMPACT. TEMPERATURES WEDNESDAY AND
WEDNESDAY NIGHT WILL BE 10 TO 15 DEGREES BELOW NORMAL BEFORE
MODERATING TO AROUND NORMAL FOR THE REMAINDER OF THE FORECAST
PERIOD. 35

AVIATION...

MVFR WITH SOME IFR CONDITIONS WILL CONTINUE THIS MORNING...WITH SOME
GENERAL IMPROVEMENT THIS AFTERNOON BEFORE MORE WIDESPREAD IFR TO
LIFR DEVELOPS TONIGHT AS THE COLD FRONT MOVES THROUGH. THE OTHER BIG
ISSUE WILL BE STRONG TSRA. STORMS ARE LIKELY TO BECOME NUMEROUS
ENOUGH FOR MENTION AS PREVAILING OR TEMPO IN MOST OF THE TAFS AT
SOME POINT LATER THIS AFTERNOON INTO EARLY TONIGHT. MANY OF THE TSRA
WILL HAVE VERY HEAVY RAIN WITH VSBYS BELOW 2 MILES. CONVECTIVE GUSTS
OF 35 TO 50 KNOTS WILL ALSO BE POSSIBLE. 22/TD

MARINE...

WINDS NEAR 15 KNOTS TODAY AHEAD OF THE COLD FRONT OUTSIDE OF
CONVECTIVE ACTIVITY. WINDS WILL RAMP UP QUICKLY BY LATE EVENING AS
COLD FRONT REACHES THE COASTAL WATERS. THIS WILL REQUIRE THE
ISSUANCE OF A GALE WARNING FOR MUCH OF THE COASTAL WATERS FOR LATE
TONIGHT AND EARLY TUESDAY MORNING AS NOTED IN THE SHORT TERM
PORTION OF THE DISCUSSION. WINDS THEN SHOULD WANE SOMEWHAT...BUT
A SMALL CRAFT ADVISORY WILL STILL BE NECESSARY AT THAT POINT
THROUGH TUESDAY NIGHT. HIGH PRESSURE WILL MOVE QUICKLY EASTWARD
WITH ONSHORE FLOW RETURNING DURING THE DAY THURSDAY WITH AT LEAST
EXERCISE CAUTION HEADLINES NECESSARY FOR PORTIONS OF THE WATERS.
35

DECISION SUPPORT...

DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
             MONITORING RIVER FLOODING.
             MONITORING CONVECTIVE AND HEAVY RAIN TRENDS.

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  43  58  33  69 /  80  10   0   0
BTR  46  61  36  70 /  70  10   0   0
ASD  48  62  35  69 /  90  10   0   0
MSY  49  61  43  68 /  80  10   0   0
GPT  51  63  38  68 /  90  20   0   0
PQL  51  62  34  68 /  90  20   0   0

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...FLASH FLOOD WATCH UNTIL 11 PM MONDAY FOR THE FOLLOWING ZONES:
     ASSUMPTION...LOWER JEFFERSON...LOWER LAFOURCHE...LOWER
     PLAQUEMINES...LOWER ST. BERNARD...LOWER
     TERREBONNE...ORLEANS...ST. CHARLES...ST. JAMES...ST. JOHN
     THE BAPTIST...ST. TAMMANY...UPPER JEFFERSON...UPPER
     LAFOURCHE...UPPER PLAQUEMINES...UPPER ST. BERNARD...AND
     UPPER TERREBONNE.

     COASTAL FLOOD ADVISORY FROM 7 PM MONDAY TO 1 PM TUESDAY FOR THE
     FOLLOWING ZONES: AND ORLEANS.

     WIND ADVISORY FROM 10 PM MONDAY TO 10 AM TUESDAY FOR THE
     FOLLOWING ZONES: LOWER JEFFERSON...LOWER LAFOURCHE...LOWER
     PLAQUEMINES...LOWER ST. BERNARD...ORLEANS...ST.
     CHARLES...ST. JOHN THE BAPTIST...UPPER JEFFERSON...UPPER
     PLAQUEMINES...AND UPPER ST. BERNARD.

GM...GALE WARNING FROM 10 PM MONDAY TO 9 AM TUESDAY 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 THE SOUTHWEST PASS OF
     THE MISSISSIPPI RIVER TO PORT FOURCHON OUT 20 NM...LAKE
     BORGNE...LAKE PONTCHARTRAIN AND LAKE MAUREPAS...AND
     MISSISSIPPI SOUND.

     SMALL CRAFT ADVISORY FROM 9 AM TUESDAY TO 6 AM WEDNESDAY 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
     THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER TO PORT
     FOURCHON OUT 20 NM...LAKE BORGNE...LAKE PONTCHARTRAIN AND
     LAKE MAUREPAS...AND MISSISSIPPI SOUND.

     SMALL CRAFT ADVISORY FROM MIDNIGHT TUESDAY TO 6 AM WEDNESDAY FOR
     THE FOLLOWING ZONES: COASTAL WATERS FROM STAKE ISLAND LA TO
     THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60
     NM...AND COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON FROM 20 TO 60 NM.

MS...FLASH FLOOD WATCH UNTIL 11 PM MONDAY FOR THE FOLLOWING ZONES:
     HANCOCK...HARRISON...AND JACKSON.

GM...GALE WARNING FROM 10 PM MONDAY TO 9 AM TUESDAY 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 THE SOUTHWEST PASS OF
     THE MISSISSIPPI RIVER TO PORT FOURCHON OUT 20 NM...LAKE
     BORGNE...LAKE PONTCHARTRAIN AND LAKE MAUREPAS...AND
     MISSISSIPPI SOUND.

     SMALL CRAFT ADVISORY FROM 9 AM TUESDAY TO 6 AM WEDNESDAY 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
     THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER TO PORT
     FOURCHON OUT 20 NM...LAKE BORGNE...LAKE PONTCHARTRAIN AND
     LAKE MAUREPAS...AND MISSISSIPPI SOUND.

     SMALL CRAFT ADVISORY FROM MIDNIGHT TUESDAY TO 6 AM WEDNESDAY FOR
     THE FOLLOWING ZONES: COASTAL WATERS FROM STAKE ISLAND LA TO
     THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60
     NM...AND COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON FROM 20 TO 60 NM.

&&

$$







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