Severe Thunderstorm Warning 114, NWS New Orleans, LA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1146 PM CDT THU MAY 31 2012

.AVIATION...
A NEARLY SOLID LINE OF CONVECTION HAS DEVELOPED ACROSS THE MID
SECTION OF THE FORECAST AREA LATE THIS EVENING ALONG WITH OTHER
ISOLATED SHOWERS AND THUNDERSTORMS. THE CONVECTION WAS DEVELOPING
IN A MOIST AND UNSTABLE ATMOSPHERE AIDED BY DIFLUENT FLOW ALOFT
AND THE TAIL END OF SOME DYNAMICS MOVING THROUGH THE AREA. THIS
CONVECTION WILL LIKELY IMPACT KASD...KMSY...KNEW...KHSA AND KGPT
PRIOR TO 08Z. OTHERWISE...MOST VFR CONDITIONS WILL PREVAIL THROUGH
THE EARLY MORNING HOURS ALTHOUGH LOCALIZED IFR CONDITIONS OR LOWER
MAY IMPACT KMCB AND PERHAPS A COUPLE OF OTHER SITES BRIEFLY BEFORE
SUNRISE. DURING THE DAY FRIDAY AS WELL AS FRIDAY EVENING...VFR
CONDITIONS ARE EXPECTED TO PREVAIL IN THE WAKE OF A COLD FRONT PASSAGE.
11

&&

.PREV DISCUSSION... /ISSUED 944 PM CDT THU MAY 31 2012/

UPDATE AND SOUNDING DISCUSSION...
UPDATED GRIDS A COUPLE TIMES AS THE SHOWERS AND THUNDERSTORMS
SWEPT THROUGH THE AREA. LOOKING AT SATELLITE AND SURFACE AND UPPER
AIR ANALYSIS...THE UPPER LEVELS AROUND 250-300 MB ARE RATHER
DIFLUENT ACROSS LOUISIANA AND MISSISSIPPI. THE 500 AND 700 MB
TROUGHS ARE APPROACHING THE WESTERN PORTION OF THE FORECAST AREA
NEAR THE LOWER MISSISSIPPI RIVER VALLEY AND SOUTH CENTRAL
LOUISIANA. THE 850 MB TO SURFACE COLD FRONTS REMAIN WELL TO THE
NORTHWEST ACROSS THE ARKLATEX REGION AND MOVEMENT HAS BEEN RATHER
SLOW. THIS FRONT SHOULD START TO ACCELERATE SLOWLY TO THE
SOUTHEAST AS THE STRONG NORTHERN STREAM PORTIONS OF THE UPPER
TROUGH PUSHES FROM THE NORTHERN PLAINS ACROSS THE MID MISSISSIPPI
VALLEY LATE TONIGHT.

THE 00Z KLIX SOUNDING HAD STABILIZED QUITE A BIT BEHIND THE STRONG
INITIAL SHORTWAVE TROUGH THAT BROUGHT THE SEVERE WEATHER TO
PORTIONS OF THE REGION. THE LI WAS ONLY MARGINALLY UNSTABLE AT -1
WITH THE LOWER LEVELS HAVING DRIED. A PRONOUNCED SURFACE INVERSION
HAD FORMED DUE TO THE RAIN COOLED AIR. WINDS IN THE LOWEST 5K FEET
AVERAGED SOUTH AT 9 KNOTS INCREASING QUITE A BIT AND VEERING TO
THE WEST AT 32 KNOTS FROM 5 TO 10K FEET. THE 00Z KLCH SOUNDING WAS
MUCH MORE UNSTABLE WITH AN LI OF -9.

GIVEN THE UNSTABLE AIR TO THE WEST AND THE STRONG DYNAMICS...HAVE
KEPT A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE FORECAST FOR
THE REMAINDER OF THE EVENING AND MUCH OF THE OVERNIGHT. ISOLATED
SHOWERS AND THUNDERSTORMS HAVE STARTED REDEVELOPING THE LAST HALF
HOUR TO HOUR NEAR THE LOWER ATCHAFALAYA RIVER AND PORTIONS OF THE
NORTHSHORE OF LAKE PONTCHARTRAIN. SEVERE THUNDERSTORMS ARE NO
LONGER EXPECTED...HOWEVER A FEW STORMS COULD PRODUCE FREQUENT
LIGHTNING STRIKES...GUSTY WINDS...AND HEAVY RAINFALL.

THE COLD FRONT IS EXPECTED TO MOVE THROUGH COASTAL SECTIONS BY MID
MORNING ON FRIDAY. THE MODELS ARE MOSTLY DRY SO HAVE UPDATED THE
GRIDS AND FORECASTS TO REMOVE MENTION OF RAIN FROM MOST OF THE
AREA ON FRIDAY AND LIMITED THE SLIGHT CHANCE OVER EASTERN AREAS
THROUGH MID MORNING BEFORE ALL AREAS DRY OUT. 22/TD

AVIATION...
DO NOT HAVE ANY MENTION OF SHRA OR TSRA IN THE TAFS SINCE THE
CHANCE OF OCCURRENCE IS ONLY 30 PERCENT. HOWEVER...MAY HAVE TO
AMEND A COUPLE LOCATIONS LATER FOR VCTS OR BRIEF TSRA IF COVERAGE
ON RADAR INCREASES. OTHERWISE...MOSTLY VFR CONDITIONS CAN BE
EXPECTED...EXCEPT FOR A FEW HOURS OF MVFR IN BR AND/OR LOWER CIGS
LATE TONIGHT AT KMCB AND KHUM.

PREV DISCUSSION... /ISSUED 322 PM CDT THU MAY 31 2012/

SHORT TERM...
MOST WEATHER CONCERNS THIS PACKAGE ARE IN THE CURRENT 6 HOURS OR
SO ASSOCIATED WITH MCV INDUCED CONVECTIVE COMPLEX ROLLING THROUGH
THE FORECAST AREA THIS AFTERNOON. THERE HAVE BEEN SEVERAL REPORTS
OF WIND DAMAGE AND HAIL ACROSS THE AREA WITH OCCASIONAL SHORT-
LIVED ROTATIONS NOTED ON RADAR FROM TIME TO TIME. NEW WATCH POSTED
FOR THE EASTERN HALF OF CWA TO RUN THROUGH 9 PM. WILL LIKELY START
SHAVING WESTERN PORTIONS OF WS327 PRIOR TO ZONE ISSUANCE IN AREAS
WHERE THREAT HAS ENDED. COLD FRONT ENTERING WESTERN LOUISIANA
SHOULD CONTINUE TO MOVE THROUGH THE AREA OVERNIGHT AND CLEAR THE
LAND AREAS BY DAYBREAK FRIDAY...PERHAPS STILL LINGERING ACROSS THE
COASTAL WATERS. HAVE NOT MADE MANY CHANGES TO FORECAST
TEMPERATURES AND RAIN CHANCES BEYOND FRIDAY AS THE TREND SEEMS TO
BE ON TRACK PER MODEL GUIDANCE.

LONG TERM...
COLD FRONT SHOULD DISSIPATE AND RETREAT NORTHWARD SUNDAY WITH DEEP
FETCHED TROPICAL FLOW BECOMING ESTABLISHED FOR MUCH OF NEXT WEEK.
THIS SHOULD BRING NEAR TO ABOVE NORMAL TEMPERATURES AND TYPICAL
DAY TO DAY RAIN CHANCES ASSOCIATED WITH GULF AND LAKE BREEZE
INTERACTIONS. MODELS IMPLYING A BERMUDA RIDGE REGIME FOR MUCH OF
THE WEEK ONCE THE FRONT GETS FLUSHED OUT OF REGION.

AVIATION...
CONVECTIVE IMPACTS AT TERMINALS TO LOWER CONDITIONS BRIEFLY TO
MVFR THROUGH ABOUT 00Z. OTHERWISE VFR CONDITIONS ARE EXPECTED
OUTSIDE CONVECTION. LARGE RAIN SHIELD BEHIND LEADING EDGE APPEARS
TO BE COMING FROM MID LAYER DECK ABOVE 070.

MARINE...
OUTSIDE OF LOCALLY ROUGH SEAS GENERATED FROM THUNDERSTORMS THIS
EVENING...SEAS SHOULD REMAIN RATHER LOW NEXT FEW DAYS UNTIL STEADY
STATE ONSHORE FLOW BECOMES ESTABLISHED MONDAY ONWARD...BRINGING A
LONG FETCHED GROUND SWELL TRAIN INTO THE COASTAL AREAS NEXT WEEK.

DECISION SUPPORT...
DSS CODE...YELLOW.
DEPLOYED...NONE.
ACTIVATION...STORM SPOTTERS/HIGH IMPACTS DESK/OZONE HAM RADIO.
ACTIVITIES...SEVERE WEATHER SURVEILLANCE/WARNING ISSUANCES.

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  66  86  58  87 /  20  10   0  10
BTR  68  88  61  88 /  20  10  10  10
ASD  68  88  61  88 /  60  10  10  10
MSY  71  87  71  88 /  60  10  10  10
GPT  69  89  64  86 /  60  20  10  10
PQL  69  87  61  88 /  50  20  10  10

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
703 PM CDT THU MAY 31 2012

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>082-020015-
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-
703 PM CDT THU MAY 31 2012

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

.DAY ONE...TONIGHT

SCATTERED THUNDERSTORMS ARE EXPECTED TO MAINLY AFFECT COASTAL
AREAS AND THE COASTAL WATERS TONIGHT. A FEW OF THESE STORMS WILL
PRODUCE FREQUENT LIGHTNING...WIND GUSTS TO 40 MPH...AND SMALL
HAIL. ELSEWHERE...THERE IS A SLIGHT CHANCE OF THUNDERSTORMS
REDEVELOPING THIS EVENING. WIDESPREAD HAZARDOUS WEATHER IS NOT
EXPECTED.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THERE IS A SLIGHT CHANCE OF THUNDERSTORMS FRIDAY MORNING MAINLY
ALONG COASTAL AREAS AND OVER THE COASTAL WATERS.
OTHERWISE...HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

THE ACTIVATION OF STORM SPOTTERS...HAM RADIO OPERATORS...AND
EMERGENCY MANAGEMENT PERSONNEL IN SUPPORT OF SEVERE WEATHER
OPERATIONS...IS NO LONGER REQUESTED.

22/TD

LAZ059>061-063-068-069-010645-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1241 AM CDT FRI JUN 1 2012

...STRONG THUNDERSTORM MOVING EAST AFFECTING ST. CHARLES PARISH...
UPPER LAFOURCHE PARISH...UPPER JEFFERSON PARISH...UPPER PLAQUEMINES
PARISH...LOWER JEFFERSON PARISH...LOWER PLAQUEMINES PARISH...

AT 1239 AM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
STRONG THUNDERSTORM 10 MILES NORTHEAST OF LAROSE...OR ABOUT 11 MILES
WEST OF BARATARIA...MOVING EAST AT 20 MPH.

THE STRONG THUNDERSTORM WILL AFFECT AREAS IN AND AROUND...
BARATARIA...JEAN LAFITTE...LAFITTE AND MYRTLE GROVE

THE PRIMARY THREATS FROM THIS STORM ARE FREQUENT LIGHTNING...SUB
SEVERE HAIL UP TO NICKEL SIZE...AND WIND GUSTS TO NEAR 40 MPH...WHICH
COULD DOWN TREE LIMBS AND BLOW AROUND UNSECURED SMALL OBJECTS. SEEK
SHELTER IN A SAFE HOME OR BUILDING UNTIL THIS STORM HAS PASSED.

BE PREPARED TO TAKE QUICK ACTION IF A WARNING IS ISSUED. STAY TUNED
TO NOAA WEATHER RADIO OR YOUR FAVORITE LOCAL MEDIA OUTLETS FOR
FURTHER DETAILS OR UPDATES FROM THE NATIONAL WEATHER SERVICE.