Severe Thunderstorm Warning 47, NWS New Orleans, LA

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1104 AM CDT FRI MAY 11 2007

.CONVECTIVE UPDATE...

WILL NOT BE MAKING ANY CHANGES TO CURRENT FORECAST PACKAGE. THE
REFRESHER ON THE HAZARDOUS WEATHER OUTLOOK WILL MENTION STRONG
THUNDERSTORMS BUT NOT QUITE SEVERE...IN LIMITED COVERAGE. SEVERAL
PROS AND CONS TO POTENTIAL TODAY. UPPER LOW OVER THE NORTHWEST
GULF IS PROVIDING A COLD POOL OF SORTS ALOFT AND A 100+KT JET
STREAK ACROSS THE MIDDLE GULF. LOW LEVEL MOISTURE IS ADEQUATE BUT
NOT TERRIBLY DEEP. PRECIPITABLE WATER VALUES AROUND 1.1-1.3 ARE IN
RANGE FOR PREFERRED SATURATION THICKNESSES OF 567DM FOR MAY.
MODELS SHOW A LARGE DIVERGENCE FEATURE DEVELOPING OVER THE AREA
BUT LOW LEVEL CONVERGENCE IS WEAK. IT MAY NEED THE SUPPORT OF SEA
AND LAKE BREEZE WINDS TO FORM THE CONVERGENCE NEEDED FOR FORCING
ALONG A SUBTLE SURFACE PRESSURE TROUGH NEAR THE LA-MS STATE LINE
BELOW MCCOMB. THIS WOULD MEAN AN ONSET PROBABLY 2 PM OR LATER.
THIS AREA IS FAIRLY CLOUD FREE AND ADJACENT TO AN EXTENSIVE CLOUD
DECK TO THE SOUTHWEST...PROVIDING SOME DIFFERENTIAL HEATING INTO
THE AFTERNOON. VERY SLOW STORM MOTIONS CAN SEND MUCH MOISTURE AND
CLOUD POLLUTION ALOFT THAT SHUTS DOWN ANY PERPETUATION BY MID TO
LATE AFTERNOON.

RICKS INDEX OUTPUT USING 332K LIFT FROM MOST UNSTABLE LIFT AT
987MB YIELDS A POP 53 PERCENT...PRECIP 2.91 INCHES...POTENTIAL
PCPN 5.72 INCHES FOR TEMP BELOW 72F. RICKS INDEX 126 GIVES A 16
PERCENT CHANCE OF SEVERE WITH CONVECTIVE GUSTS 46 KT
/41-51KT/...FORECAST HAIL SIZE 0.44 INCHES /PEA/ WITH A VIL OF 56.
THE ARKANSAS METHOD VIL OF THE DAY IS 49. TOR THREAT IS EF0 AND
WATERSPOUTS POSSIBLE. HAIL-VIL SHOWS A 59 VIL NEEDED FOR PENNY
HAIL. DOWNBURST CHECKLIST SHOWS A MODERATE RISK OF DOWNBURST WINDS
ASSUMING CAPE VALUES GREATER THAN 2000 J/KG.

BOTTOM LINE IS ANTICIPATING SCATTERED SLOW MOVING THUNDERSTORMS TO
DEVELOP ALONG WEAK SURFACE TROUGH NORTH OF LAKE PONTCHARTRAIN ONCE
LAKE BREEZE KICKS IN. CONVECTIVE INTIATION TEMP IS AROUND
84F...CLOSE TO FORECAST MAX TEMPS THIS AFTERNOON. STRONG TO MARGINAL
SEVERE WITH RICKS INDEX OUTPUT AS BASIS AND IN AGREEMENT WITH SEE
TEXT COMMENTS OF STORM PREDICTION CENTER. AS UPPER LEVELS
MOISTEN...EXPECTING CONVECTION TO TRANSITION TO HIGH BASED
STRATIFORM WITH EXTENSIVE CLOUD COVER IN COLD POOL SIMILAR TO A
WARM TOPPED MCS. THEREFORE...PRIMARY THREAT OF CONVECTIVE IMPACTS
WILL BE A SMALL WINDOW FROM INITIATION TO TOPSIDE SATURATION...
MAINLY BETWEEN 2 AND 5 PM. HWO OUT SHORTLY.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  86  61  86  63 /  30  20  20  30
BTR  84  64  86  65 /  30  20  20  30
MSY  84  66  86  67 /  30  20  10  20
GPT  85  64  87  66 /  30  20  20  30

&&

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

24

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1112 AM CDT FRI MAY 11 2007

LAZ034>040-046>050-056>070-MSZ068>071-077-080>082-120300-
POINTE COUPEE-WEST FELICIANA-EAST FELICIANA-ST. HELENA-TANGIPAHOA-
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-WILKINSON-AMITE-PIKE-WALTHALL-
PEARL RIVER-HANCOCK-HARRISON-JACKSON-
1112 AM CDT FRI MAY 11 2007

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
LOUISIANA AND SOUTHERN MISSISSIPPI.

.DAY ONE...THIS AFTERNOON AND TONIGHT
SCATTERED STRONG TO MARGINALLY SEVERE THUNDERSTORMS MAY DEVELOP IN
THE DAYTIME HEATING BY MID-AFTERNOON TODAY...PRIMARILY NORTH AND
WEST OF THE LOUISIANA TIDAL LAKES INTO SOUTHWEST MISSISSIPPI. THE
PRIMARY THREAT WILL BE LOCALIZED DOWNBURST WINDS GUSTS NEAR 50 MPH
AND PEA TO MARBLE SIZED HAIL FROM THE STRONGER STORMS THAT MAY
FORM BETWEEN 2 PM AND 5 PM. DUE TO SLOW MOVING NATURE OF ANY
STORMS...LOCALLY HEAVY RAINFALL MAY PRODUCE SOME PONDING OF WATER
AND ISOLATED ACCUMULATIONS OF 3 TO 5 INCHES OF RAINFALL. DUE TO
THE LIMITED EXTENT OF COVERAGE...A WIDESPREAD SEVERE OR FLOOD
THREAT IS NOT EXPECTED.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A CHANCE OF THUNDERSTORMS MAINLY SUNDAY AND LATE
WEDNESDAY INTO THURSDAY. AT THIS TIME...NO HAZARDOUS WEATHER IS
EXPECTED.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT REQUIRED TODAY. HOWEVER ONE OR TWO
STORMS MAY BRIEFLY APPROACH SEVERE LEVELS. LAW ENFORCEMENT AND
EMERGENCY MANAGERS ARE URGED TO NOTIFY THE NATIONAL WEATHER
SERVICE IF HIGH WINDS OR HAIL IS REPORTED THIS AFTERNOON.

24

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
310 PM CDT FRI MAY 11 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0303 PM     HAIL             8 W GULFPORT            30.39N 89.20W
05/11/2007  E1.75 INCH       HARRISON           MS   TRAINED SPOTTER

            GOLFBALL SIZE HAIL REPORTED ON KILN-DELISLE ROAD. REPORT
            RELAYED BY WLOX RADIO STATION.

&&

RSW

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
333 PM CDT FRI MAY 11 2007

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0331 PM     HAIL             KILN                    30.42N 89.43W
05/11/2007  E1.25 INCH       HANCOCK            MS   EMERGENCY MNGR

            REPORT FROM HANCOCK COUNTY EOC.

&&

RSW