Special Weather Statement, NWS New Orleans, LA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1135 AM CDT THU MAY 21 2015

.UPDATE...

FORECAST REASONING FROM SOUNDING DISCUSSION ALONG WITH
RADAR...MESO-ANALYSIS...AND HRRR MODEL TRENDS ALL SUPPORT RAISING
THE POP TO LIKELY RANGE FOR MUCH OF THE AREA THE REMAINDER OF
TODAY. TEMPERATURES WERE RISING A BIT FASTER AND ALREADY REACHED
THE FORECAST HIGHS. ANOTHER RISE OF A DEGREE OR TWO IS
POSSIBLE...HOWEVER INCREASING SHOWERS AND THUNDERSTORMS AND
ASSOCIATED CLOUD COVER WILL BE CAPPING OFF THE TEMPERATURES AND
CAUSING A GENERAL DOWNTREND AS THE AFTERNOON PROGRESSES. UPDATES
HAVE BEEN SENT. 22/TD

&&

.PREV DISCUSSION... /ISSUED 757 AM CDT THU MAY 21 2015/

..SOUNDING DISCUSSION...

PLENTY OF MOISTURE POOLING AHEAD OF THE WEAK FRONT CURRENTLY
LOCATED OVER NORTHERN LOUISIANA AND SOUTHERN MISSISSIPPI. PW IS
ABOUT 150% OF NORMAL FOR LATE MAY. AN INVERSION FROM THE SURFACE
TO 1000 FEET IS CAPPING THE ATMOSPHERE NOW...BUT WILL MIX OUT
WITH DAYTIME HEATING. PLENTY OF INSTABILITY WITH MLCAPE AROUND
1900 J/KG WITH ML LI OF -6 AND A 500MB TEMPERATURE OF -10C. WITH
THIS INSTABILITY...GOOD MOISTURE...AND THE FRONT AND ANY SEA
BREEZE BOUNDARIES BEING LIFTING MECHANISMS...STRONG TO PERHAPS
SEVERE STORMS WILL BE POSSIBLE TODAY. MAIN CONCERN WOULD BE STRONG
WIND GUSTS WITH A LESSER CHANCE OF HAIL GIVEN HIGH FREEZING LEVEL
AROUND 13700 FEET AND WET BULB ZERO ABOUT 2000 LESS THAN THAT.
THERE IS NOT MUCH IN THE WAY OF DIRECTIONAL WIND SHEAR ON THE
CURRENT SOUNDING WITH ALL WINDS HAVE A WESTERLY COMPONENT. BUT AS
THE FRONT NEARS MAY GET A BIT MORE DIRECTIONAL SHEAR. ONE LAST
THING TO MENTION IS WE MAY SEE A FEW THUNDERSTORMS DEVELOP AHEAD
OF THE FRONT WITH A CONVECTIVE TEMPERATURE CALCULATED AT
82F. CURRENT FORECAST HAS US REACHING 82F AROUND 16-17Z AND 11Z
HRRR HAS PRECIPITATION FORMING AROUND THEN TOO.

12Z BALLOON INFO: NO ISSUES WITH THE FLIGHT THAT LASTED 94 MINUTES
AND ASCENDED TO A HEIGHT OF 20.4 MILES ABOVE THE GROUND. THE
BALLOON BURST 21 MILES DOWNRANGE FROM THE OFFICE NEAR ANSLEY.

ANSORGE

PREV DISCUSSION... /ISSUED 430 AM CDT THU MAY 21 2015/

SYNOPSIS...
LATEST SURFACE ANALYSIS SHOWED A 1011MB LOW OVER WESTERN TENNESSEE
WITH A FRONTAL BOUNDARY EXTENDING SOUTHWEST TO WEST CENTRAL
ALABAMA TO WEST CENTRAL MISSISSIPPI TO WEST CENTRAL LOUISIANA.
A 1024MB HIGH WAS LOCATED OVER NEBRASKA/KANSAS. UPPER AIR
ANALYSIS SHOWED A HIGH OVER MEXICO...DISTURBANCE RIDING ON TOP OF THE
RIDGE OVER TEXAS AND A POSITIVELY TILTED TROUGH FROM GREAT LAKES
TO IOWA. IR SHOWED CLOUD COOLING AND SEVERAL THUNDERSTORM COMPLEX
EAST OF THE BIG BEND TO NORTH CENTRAL TEXAS. RADAR REVEALED
ISOLATED CONVECTION ALONG THE FRONT OVER SOUTHERN MISSISSIPPI AND
EAST CENTRAL LOUISIANA.

DISCUSSION...
FRONTAL BOUNDARY WILL CONTINUE TO PUSH SOUTH INTO THE FORECAST
AREA TODAY. SURFACE HEATING WILL INCREASE INSTABILITY AND SURFACE
CONVERGENCE WILL YIELD SCATTERED CONVECTION TODAY. WITH THE
FRONTAL BOUNDARY PUSHING SOUTH THROUGH THE AREA TONIGHT...THE
THREAT OF CONVECTION WILL CONTINUE OVERNIGHT. UPPER LEVEL TROUGH
UP NORTH WILL SWING SOUTH ... GREAT LAKES AND MID ATLANTIC
REGIONS. SURFACE HIGH ON THE PLAINS WILL PRESS SOUTHEAST OVER THE
MID SOUTH THROUGH FRIDAY AND DRY AIR WILL FILTER IN AS EARLY AS
THIS AFTERNOON ACROSS THE NORTH ZONES.

THE FRONTAL BOUNDARY IS EXPECTED TO PUSH SOUTH INTO THE CENTRAL
GULF COAST REGION TONIGHT AND LINGERS ACROSS THE AREA ON FRIDAY
BEFORE BECOMING DIFFUSE ON SATURDAY. HIGH PRESSURE WILL SETTLE
OVER THE EAST AND SOUTHERLY FLOW DEVELOP OVER THE LOWER
MISSISSIPPI VALLEY AND FORECAST AREA SATURDAY AFTERNOON. A
BUILDING UPPER LEVEL RIDGE OVER THE CENTRAL U.S AT THE END OF WEEK
WILL TRAVERSE INTO THE EASTERN CONUS OVER THE WEEKEND. THIS UPPER
LEVEL RIDGE ALONG WITH OVERALL DRIER AIR IN THE ATMOSPHERIC COLUMN
SHOULD HAMPER MOST CONVECTION ON SATURDAY...ISOLATED FOR WEST
ZONES. RAIN CHANCES WILL START TO GO UP AGAIN ON SUNDAY AS THE
UPPER RIDGE AXIS SHIFTS TO THE EAST OF THE REGION AND DISTURBANCES
IN THE SOUTHWEST FLOW ALOFT AHEAD OF A WESTERN CONUS SYSTEM BEGIN
TO IMPACT THE REGION. THIS PATTERN WILL CONTINUE THROUGH THE EARLY
PART OF NEXT WEEK WITH DAILY CHANCES FOR SCATTERED CONVECTION.

AVIATION...
FOG SHOULD ONLY AFFECT THE HOUMA TERMINAL THIS MORNING. CEILINGS
SHOULD STAY ABOVE 015 THIS MORNING AS WELL. WILL SHOW VCTS FOR TODAY
AT ALL SITES. IT LOOKS LIKE THERE WILL BE TWO WAVES OF SH/TS...ONE
DURING THE MORNING AS THE BOUNDARY SINKS SOUTHWARD THEN AGAIN IN THE
AFTERNOON AS HEATING AND BOTH THE FRONTAL BOUNDARY AND C-BRZ
BOUNDARIES BEGIN TO ENHANCE ACTIVITY DURING THE AFTERNOON AND EARLY
EVENING. NOT EXPECTING TO SEE ANY LARGE RESTRICTIONS IN VIS
OVERNIGHT AND CEILINGS SHOULD STAY AROUND 020 FOR THE MOST PART.

MARINE...LIGHT WIND REGIME EXPECTED TO PERSIST TODAY BUT STILL
LOOKS LIKE A WEAK NOCTURNAL JET OVER THE MS SOUND AND JUST TO THE
SOUTH WILL DEVELOP THE NEXT FEW NIGHTS CAUSING WINDS TO STRENGTHEN
IN THESE AREAS TO NEAR OR JUST OVER 10 KTS. HIGH PRESSURE SLIDES
THROUGH THE AREA TODAY/FRIDAY AS A WEAK FRONT TRIES TO PUSH INTO THE
COASTAL WATERS. HIGH PRESSURE WILL QUICKLY SHIFT EAST AND MODERATE
ONSHORE FLOW WILL DEVELOP OVER THE WEEKEND.

DECISION SUPPORT...
DSS CODE...GREEN...UPGRADE TO YELLOW POSSIBLE THIS AFTERNOON.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...MONITORING STRONG TO SEVERE THUNDERSTORM POTENTIAL
TODAY.

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 RISK SVR AND/OR DIRECT
         TROPICAL THREATS; EVENTS OF NATIONAL SIGNIFICANCE

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  82  62  81  65 /  60  20  40  20
BTR  86  65  82  68 /  60  30  40  20
ASD  86  67  80  68 /  60  30  40  20
MSY  86  73  84  73 /  60  30  40  20
GPT  86  68  80  71 /  50  30  40  20
PQL  86  66  81  68 /  50  30  40  10

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1102 AM CDT THU MAY 21 2015

GMZ530-532-534-536-538-550-552-555-557-570-572-575-577-LAZ034>037-
039-040-046>050-056>072-MSZ068>071-077-080>082-220415-
LAKE PONTCHARTRAIN AND LAKE MAUREPAS-MISSISSIPPI SOUND-
LAKE BORGNE-CHANDELEUR SOUND-BRETON SOUND-
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-
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 OUT 20 NM-
COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA RIVER FROM
20 TO 60 NM-
COASTAL WATERS FROM THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER
TO PORT FOURCHON 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 PASCAGOULA MS TO STAKE ISLAND LA FROM 20 TO
60 NM-POINTE COUPEE-WEST FELICIANA-EAST FELICIANA-ST. HELENA-
WASHINGTON-ST. TAMMANY-IBERVILLE-WEST BATON ROUGE-
EAST BATON ROUGE-ASCENSION-LIVINGSTON-ASSUMPTION-ST. JAMES-
ST. JOHN THE BAPTIST-UPPER LAFOURCHE-ST. CHARLES-UPPER JEFFERSON-
ORLEANS-UPPER PLAQUEMINES-UPPER ST. BERNARD-UPPER TERREBONNE-
LOWER TERREBONNE-LOWER LAFOURCHE-LOWER JEFFERSON-
LOWER PLAQUEMINES-LOWER ST. BERNARD-NORTHERN TANGIPAHOA-
SOUTHERN TANGIPAHOA-WILKINSON-AMITE-PIKE-WALTHALL-PEARL RIVER-
HANCOCK-HARRISON-JACKSON-
1102 AM CDT THU MAY 21 2015

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
LOUISIANA...SOUTH MISSISSIPPI AND THE ADJACENT COASTAL WATERS.

.DAY ONE...TODAY AND TONIGHT

SCATTERED TO NUMEROUS THUNDERSTORMS ARE EXPECTED THIS AFTERNOON
AND EVENING AS A WEAK COLD FRONT MOVES INTO THE AREA. A FEW
STRONG TO SEVERE THUNDERSTORMS WILL BE POSSIBLE...WITH THE
PRIMARY THREATS BEING STRONG GUSTY WINDS...FREQUENT
LIGHTNING...HAIL...AND LOCALLY HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED EACH DAY.
ORGANIZED SEVERE WEATHER IS NOT ANTICIPATED AT THIS TIME...THOUGH
A FEW STORMS COULD BECOME STRONG EACH AFTERNOON. THE PRIMARY
THREATS FROM ANY THUNDERSTORMS WILL BE FREQUENT LIGHTNING...GUSTY
WINDS AND HEAVY RAINFALL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

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