Severe Thunderstorm Warning 135, NWS New Orleans, LA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
344 PM CDT THU MAY 22 2008

.SHORT TERM...

A STRONG SHORT WAVE TROUGH SLIDING THROUGH THE CENTRAL GULF COAST...AND
ASSOCIATED JET MAX MOVING THROUGH THE EASTERN GULF OF MEXICO WILL
CONTINUE TO BRING UNSETTLED WEATHER TO THE CWA EARLY TONIGHT. HAVE
WENT WITH HIGH END CHANCE POPS FOR EASTERN AND SOUTHERN
ZONES...WITH LOW END CHANCE POPS ELSEWHERE. HEAVY RAINS WILL
MAINLY FALL SOUTH AND EAST OF LAKE PONTCHARTRAIN THROUGH THIS
EVENING...BEFORE THE RAINFALL PULLS TOWARD THE FLORIDA
PANHANDLE...AS THE STRONG MOISTURE CONVERGENCE AND DEEPER MOISTURE
POOL IS IN PLACE OVER THIS REGION AS INDICATED BY MSAS AND LAPS
ANALYSIS. WATER VAPOR AND GOES SOUNDER DATA INDICATE SOME STRONG
NEGATIVE VORTICITY ADVECTION TAKING PLACE BEHIND THE SHORTWAVE
TROUGH. THIS NVA SHOULD OVERSPREAD THE REGION TONIGHT...LEADING TO
LOWER POPS AND A SOMEWHAT DRIER AIRMASS.

TOMORROW...STRONG UPPER LEVEL RIDGING WILL BUILD ACROSS THE GULF
SOUTH. HOWEVER...THE RIDGE WILL CONTINUE TO HAVE SOME LOW AND MID-
LEVEL MOISTURE IN PLACE...WHICH WILL ALLOW FOR THE CONTINUED
DEVELOPMENT OF DIURNALLY FORCED CONVECTION. HAVE WENT WITH LOW END
CHANCE POPS FRIDAY AND SATURDAY DUE TO THIS LINGERING MOISTURE.
THE CONVECTION WILL TEND TO INITIATE ALONG MESO-SCALE BOUNDARIES
SUCH AS SEABREEZE AND LAKEBREEZE FRONTS AND OUTFLOW BOUNDARIES
FROM PREVIOUS CONVECTION. IN ADDITION...THE THUNDERSTORMS SHOULD
BE NEARLY STATIONARY FRIDAY AND SATURDAY...DUE TO LACK OF STRONG
FLOW ALOFT. THE THUNDERSTORM ACTIVITY WILL TEND TO DIE OFF SHORTLY
AFTER SUNSET...WITH MAINLY DRY CONDITIONS EXPECTED FRIDAY AND
SATURDAY NIGHTS. DUE TO THE STRONG RIDGING ALOFT...AND RESULTANT
SUBSIDENCE...TEMPERATURES WILL BE ABOVE NORMAL THROUGH SATURDAY.

.LONG TERM...

THE STRONG UPPER LEVEL RIDGE WILL REMAIN IN PLACE THROUGH THE
REMAINDER OF THE MEMORIAL DAY WEEKEND...AS A CLASSIC OMEGA BLOCK
PATTERN ESTABLISHES ITSELF OVER THE CONUS. WITH THE STRONG
RIDGING ALOFT...SUBSIDENCE AND DRY AIR IN THE MIDDLE AND UPPER
LEVELS WILL LEAD TO SOME CAPPING. THIS WILL TEND TO LIMIT MOST
CONVECTIVE DEVELOPMENT IN THE REGION. HOWEVER...A BACK DOOR COLD
FRONT WILL SLIP THROUGH THE REGION SATURDAY NIGHT AND STALL OVER
THE AREA ON SUNDAY. THIS FRONT WILL REMAIN IN PLACE THROUGH
MONDAY...AND SERVE AS A FOCUSING MECHANISM FOR AFTERNOON AND
EVENING CONVECTION EACH DAY. TEMPERATURES WILL REMAIN QUITE
WARM...DUE TO THE THERMAL RIDGING ASSOCIATED WITH THE UPPER LEVEL
ANTICYCLONE. WITH THESE WARM TEMPERATURES...CONVERGENCE ALONG THE
FRONT...AND A FAIRLY UNSTABLE ENVIRONMENT IN THE LOW LEVELS...THE
POTENTIAL FOR BREAKING THE CAP EXISTS. THUS...HAVE WENT WITH LOW
END CHANCE POPS THROUGH THE WEEKEND. ANY CONVECTION WILL BE
DIURNAL IN NATURE...WITH LITTLE PRECIPITATION EXPECTED OVERNIGHT.

BY TUESDAY...THE UPPER LEVEL RIDGE WILL SHIFT EASTWARD AND BREAK
DOWN AS A TROUGH RACES THROUGH THE NORTHERN PLAINS AND INTO THE
NORTHEASTERN STATES. HOWEVER...AT THE SURFACE...A MUCH DRIER
AIRMASS SHOULD ADVECT IN FROM THE NORTHEAST...AS THE BACK DOOR
COLD FRONT FINALLY PULLS WEST OF THE AREA. THIS DRIER AIRMASS AT
THE SURFACE...ALONG WITH CONTINUED STRONG CAPPING ALOFT SHOULD
SEVERELY LIMIT CONVECTIVE DEVELOPMENT TUESDAY AND WEDNESDAY. HAVE
WENT WITH A DRY FORECAST BOTH DAYS. WITH STRONG SOLAR INSOLATION
AND A DRIER AIRMASS...TEMPERATURES SHOULD BE ABOVE NORMAL.

A SECONDARY SURGE OF ENERGY IN THE NORTHERN STREAM WILL ALLOW FORM
A DEEPENING OF THE EASTERN TROUGH...AND THE ESTABLISHMENT OF
ANOTHER OMEGA BLOCKING PATTERN BY THE MIDDLE OF NEXT WEEK. AS THE
TROUGH DIGS SOUTHWARD...A COLD FRONT WILL SWEEP DOWN FROM THE
MIDWEST INTO THE LOWER MISSISSIPPI VALLEY. UPPER LEVEL RIDGING
OVER THE GULF SOUTH WILL BREAK DOWN...ALLOWING THE CAP TO WEAKEN.
WITH SOUTHERLY FLOW OFF THE GULF CONTINUING...A HIGHLY UNSTABLE
AIRMASS SHOULD BE IN PLACE. THUS...HAVE PUT BACK IN SLIGHT CHANCE
POPS FOR WEDNESDAY AND THURSDAY.

&&

.AVIATION...

ONGOING CONVECTION WILL CONTINUE TO IMPACT THE TERMINALS THROUGH
AT LEAST 00Z. PERIODS OF STRONG WINDS OVER 20 KNOTS AND IFR
CONDITIONS CAN BE EXPECTED WITH THESE CONVECTIVE BANDS. THE SHORT
WAVE TROUGH PRODUCING THE CONVECTION WILL PULL TO THE EAST
OVERNIGHT...WITH SOME RIDGING BUILDING IN LATE. CONDITIONS SHOULD
IMPROVE TO VFR AFTER 00Z...WITH ONLY A MIDLEVEL DECK OF CLOUDS
EXPECTED. HOWEVER...AROUND 12Z SOME FOG COULD DEVELOP AROUND KMCB
AND KBTR. CONDITIONS COULD DROP DOWN TO IFR IN KMCB FOR A BRIEF
PERIOD OF TIME DUE TO THE FOG. BY 14Z...MVFR CONDITIONS ARE
EXPECTED AT THE TERMINALS...AS A BROKEN DECK OF STRATOCUMULUS
DEVELOPS.

&&

.MARINE...

STRONG GRADIENT FLOW OF 15 TO 20 KNOTS WILL CONTINUE OVERNIGHT
INTO TOMORROW MORNING AS A SHORT WAVE TROUGH AND UPPER LEVEL JET
MAX MOVES THROUGH THE GULF. SEAS WILL ALSO REMAIN HIGH AT 3 TO 6
FEET...WHICH HAS PROMPTED THE ISSUANCE OF EXERCISE CAUTION
ADVISORIES FOR SMALL CRAFT FOR THE OFFSHORE COASTAL WATERS. BY
TOMORROW AFTERNOON...THE GRADIENT FLOW WILL WEAKEN CONSIDERABLY AS
HIGH PRESSURE SETTLES OVER THE AREA. LIGHT WINDS AND CALM SEAS
WILL BE THE RULE THROUGH THE REST OF MEMORIAL DAY WEEKEND.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  68  92  73  92 /  30  30  20  30
BTR  69  92  73  93 /  30  30  20  30
MSY  73  89  74  90 /  50  40  20  30
GPT  72  87  73  89 /  50  40  20  30

&&

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

32

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1059 AM CDT THU MAY 22 2008

GMZ530-550-555-570-575-LAZ034>040-046>050-056>070-MSZ068>071-077-
080>082-231100-
PASCAGOULA TO SW PASS MISSISSIPPI RIVER OUT 20 NM-
PASCAGOULA TO SW PASS MISSISSIPPI RIVER 20-60 NM OUT-
SW PASS MISSISSIPPI RIVER TO ATCHAFALAYA RIVER OUT 20 NM-
SW PASS MISSISSIPPI RIVER TO ATCHAFALAYA RIVER 20-60 NM OUT-AMITE-
ASCENSION-ASSUMPTION-EAST BATON ROUGE-EAST FELICIANA-HANCOCK-
HARRISON-IBERVILLE-JACKSON-LAKES PONTCHARTRAIN AND MAUREPAS-
LIVINGSTON-LOWER JEFFERSON-LOWER LAFOURCHE-LOWER PLAQUEMINES-
LOWER ST BERNARD-LOWER TERREBONNE-ORLEANS-PEARL RIVER-PIKE-
POINTE COUPEE-ST CHARLES-ST HELENA-ST JAMES-ST JOHN THE BAPTIST-
ST TAMMANY-TANGIPAHOA-UPPER JEFFERSON-UPPER LAFOURCHE-
UPPER PLAQUEMINES-UPPER ST BERNARD-UPPER TERREBONNE-WALTHALL-
WASHINGTON-WEST BATON ROUGE-WEST FELICIANA-WILKINSON-
1059 AM CDT THU MAY 22 2008

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS WILL CONTINUE TO DEVELOP TODAY ACROSS
SOUTHEAST LOUISIANA AND SOUTHERN MISSISSIPPI. AN ISOLATED STRONG OR
SEVERE THUNDERSTORM WILL BE POSSIBLE DURING THE AFTERNOON OR EARLY
EVENING. THE MAIN THREAT FROM MOST OF THE THUNDERSTORMS WILL BE
LOCALLY HEAVY RAINFALL AND FREQUENT LIGHTNING STRIKES.  HOWEVER...A
FEW OF THE STRONGEST STORMS COULD PRODUCE SMALL HAIL AND GUSTY WINDS.
THE THUNDERSTORM ACTIVITY SHOULD BEGIN TO DISSIPATE LATE THIS
EVENING.

HIGH FLOWS AND FLOODING WILL CONTINUE AT POINTS ALONG THE
MISSISSIPPI...ATCHAFALAYA...AND PEARL RIVERS. PLEASE REFER TO THE
LATEST RIVER FLOOD STATEMENTS FOR UPDATED INFORMATION.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

SCATTERED AFTERNOON AND EARLY EVENING THUNDERSTORMS ARE EXPECTED
THROUGH THE WEEKEND. THE MAIN HAZARD WILL BE FREQUENT LIGHTNING AND
LOCALLY HEAVY RAINFALL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED.

32

LAZ059-065-066-230100-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
659 PM CDT THU MAY 22 2008

...THUNDERSTORM WITH HEAVY RAIN MOVING OVER RAIN SOAKED AREAS...

AT 654 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
A CLUSTER OF THUNDERSTORMS WITH HEAVY RAINFALL...15 MILES WEST OF
HOUMA...OR ABOUT 12 MILES SOUTHWEST OF GRAY...MOVING NORTHEAST
AT 15 TO 20 MPH.

THE THUNDERSTORM WITH HEAVY RAINFALL WILL BE NEAR...GRAY AND
SCHRIEVER AT 730 PM...LOCKPORT AT 745 PM...RACELAND AND MATHEWS AT
800 PM...

EXPECT HEAVY RAINFALL IN THE PATH OF THE STORM. LOCALIZED RAINFALL
AMOUNTS OF UP TO 2 INCHES ARE POSSIBLE. MOTORISTS SHOULD WATCH OUT
FOR PONDING OF WATER ON ROADWAYS AND POOR DRAINAGE FLOODING.

BE PREPARED TO TAKE QUICK ACTION IF A FLASH FLOOD 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.

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