Severe Thunderstorm Warning 74, NWS New Orleans, LA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1119 AM CDT WED MAR 30 2016

.UPDATE...

UPDATED FORECAST TO REFLECT CURRENT TRENDS WHICH IS NO RAIN ON
RADAR/NO WEATHER...TRANSITIONING TO A SLIGHT CHANCE OF SHOWERS
EARLY THIS AFTERNOON THEN HIGHER CHANCES OF SHOWERS AND
THUNDERSTORMS BY MID TO LATE AFTERNOON. THE EXCEPTION WILL BE FOR
THE SOUTHEAST/EAST COASTAL AREAS THAT WILL LIKELY NOT SEE MUCH IF
ANY CONVECTION TODAY. AS MENTIONED IN THE SOUNDING
DISCUSSION...AND UPPER LEVEL INVERSION NEAR 340 MB IS LIMITING
CAPE TODAY...DRAMATICALLY SO COMPARED TO YESTERDAY WHEN BOTH LARGE
CAPE AND STEEP MID LEVEL LAPSE RATES SUPPORTED THE SEVERE CRITERIA
HAIL THAT OCCURRED YESTERDAY AFTERNOON. GFS MODEL SOUNDINGS
INDICATE THE UPPER LEVEL INVERSION WILL LOWER FURTHER TODAY
LOWERING THE POTENTIAL CAPE. CURRENT RADAR DEPICTION WITH A
GROWING RING OF LOW 5 TO 15 DBZ RETURNS IS LIKELY VERIFICATION
THAT THE INVERSION IS IN FACT LOWERING. EVEN WITH THESE
NEGATIVES...THERE IS STILL ENOUGH DYNAMICS...INSTABILITY AND LIFT
WITH DAYTIME HEATING FOR SCATTERED SHOWERS AND THUNDERSTORMS LATER
THIS AFTERNOON...HOWEVER SEVERE THUNDERSTORM POTENTIAL WILL LIKELY
REMAIN NEGLIGIBLE UNTIL LATER THIS EVENING OR OVERNIGHT WHEN BOTH
KINEMATIC AND THERMODYNAMIC PROFILES WILL BECOME MORE FAVORABLE
NORTH OF I-12 AND WEST OF I-59. 22/TD

&&

.PREV DISCUSSION... /ISSUED 814 AM CDT WED MAR 30 2016/

..SOUNDING DISCUSSION...

SOUNDING SHOWS AN ABOVE AVERAGE AMOUNT OF MOISTURE IN AIR COLUMN
WITH A PWAT VALUE OF 1.31 INCHES. THIS MEANS THE LOW LEVEL MOISTURE
IS STILL ON THE INCREASE FOR SOME POTENTIALLY HEAVY RAINS LATER
THIS WEEK. BROAD INVERSION NEAR 970 MB (1300 FT) TO 800 MB (6600
FT) WILL HELP DELAY MUCH OF THE CONVECTION TODAY. ADDITIONALLY
THERE IS SOME INSTABILITY ABOVE THIS INVERSION WITH 3-6 KM LAPSE
RATES NEAR 7 C/KM BUT AN UPPER LEVEL INVERSION NEAR 340 MB (28
KFT) KEEPS CAPE VALUES BELOW 900 J/KG. THIS WILL MITIGATE ANY
SEVERE STORMS. AN INTERESTING NOTE IS THAT THE DCAPE VALUE IS
ABOVE 1000 J/KG WHICH MEANS ANY STORMS THAT DO FORM LATER COULD
GENERATE GUSTY WINDS OF 20+ KTS. VEERING WINDS STILL DOMINATE THE
AIR PROFILE WITH EAST WINDS AT THE SURFACE BECOMING WESTERLY
ALOFT. MAX WINDS ARE 149 KTS AT 170 MB (43 KFT).

DRJ

PREV DISCUSSION... /ISSUED 336 AM CDT WED MAR 30 2016/

SHORT TERM...
THE NEXT 48 HOURS OR SO COULD BE ACTIVE AS ONSHORE FLOW MAINTAINS
MOIST AND UNSTABLE AIR MASS OVER A LARGE PORTION OF THE PLAINS
STATES AND MISSISSIPPI VALLEY. DEVELOPING SURFACE CYCLOGENESIS
OVER CENTRAL HIGH PLAINS WILL MOVE EAST AND NORTHEAST AND BRING
SOME LOW LEVEL CONVERGENCE INTO THE MISSISSIPPI VALLEY LATER
TODAY. THIS IS A COMPLEX SITUATION IN THAT INITIAL SURFACE
REFLECTION RACES INTO OHIO VALLEY BY THIS EVENING WHILE MORE
PRESSURE FALLS TAKE PLACE BACK OVER THE CENTRAL PLAINS UNDER LARGE
CUT-OFF LOW ALOFT. THE INITIAL LOW DOES FOCUS THE LOW LEVEL
MOISTURE IN PRE-FRONTAL OR TROWAL LINEAR FASHION OVERNIGHT THAT
WILL LIKELY BE IN THE FORM OF A LARGE MCS OR MCC NEAR THE I-20
CORRIDOR AND EXTENDING SOUTHWARD TO THE GULF COAST ON OPTIMAL INFLOW.

LOOKED EXTENSIVELY AT CHAP...SOUNDING ANALYSIS AND UPPER CHARTS TO
BETTER DETERMINE THE SEVERE THREAT OVER THE CWA. OBJECTIVE CHAP
RUN ON 00Z GFS DATA FOR KMCB DOES PING ON LOW END SEVERE TSTM
POTENTIAL WITH A RI 140...PROB SVR 30-35 PERCENT FOR GUSTS 58-60
KT /67-70 MPH/...LOW END EF-1 TORNADO POTENTIAL AND MARBLE TO DIME
SIZED HAIL IN THE OVERNIGHT HOURS. THE NAM OUTPUT WAS SUB-SEVERE.
THE OTHER LOCATIONS REMAINED BELOW SEVERE LEVELS WITH A GENERAL
CONSENSUS OF GUST POTENTIAL 40-50 MPH AND PEA TO MARBLE HAIL ON
RI VALUES CLOSER TO 120. IN SHORT...BETTER CHANCES ARE ON THE
NORTHERN FRINGES OF CWA IN SW MISSISSIPPI AND INCREASING IN
SEVERITY POTENTIAL INTO JAN CWA. THIS FITS WELL WITH SPC OUTLOOK
FOR THE NEXT 24 HOURS OR SO. QPF FOR THIS EVENT DOES BULK UP TO
AROUND 1.5-2.0 INCHES IN 6 HOURS ALONG THE BETTER FOCAL
AXIS...WITH AMOUNTS GENERALLY LESS THAN 1 INCH ON THE FLANKS.
HEADING INTO THURSDAY NIGHT...THE MODELS ARE MORE SUGGESTIVE OF
LARGE SCALE RAINFALL AND SUB-SEVERE STORMS AS OUTFLOWS PUSH BEST
FOCUS CLOSER TO THE GULF COAST AND RAIN COOLED MESO-HIGH PROCESSES
MAINTAINING GENERAL RAINFALL THROUGH BETTER PART OF THE NIGHT
THURSDAY NIGHT BEFORE IMPROVING FRIDAY MORNING FROM WEST TO EAST.
ONE CONSIDERATION WILL BE FAVORABLE PLACEMENT OF UPPER JET STREAM
STRUCTURE OVER THE GULF STATES THAT COULD BE BROUGHT DOWNWARD
BEHIND ORGANIZED CONVECTION IN THE FORM OF BOWING LINE SEGMENTS
AND SUPERCELLS WITH STRONG REAR FLANK DOWNDRAFTS. WENT PRETTY
CLOSE TO MODEL BLENDS WITH A LITTLE WEIGHT TOWARDS GFS ON TEMPS
AND POPS THROUGH FRIDAY. 24/RR

LONG TERM...
AFTER FRIDAY CLEARING THE REMAINDER OF THE FORECAST PACKAGE SHOULD
REMAIN DRY AND SEASONABLY WARM WITH LITTLE IN THE WAY OF IMPACTFUL
WEATHER THROUGH WEDNESDAY UNDER THE INFLUENCE OF CONTINENTAL HIGH
PRESSURE. 24/RR

AVIATION...
A MIX OF IFR AND MVFR CEILINGS HAVE DEVELOPED OVER THE LAST COUPLE
OF HOURS IN RESPONSE TO A STRENGTHENING ELEVATED INVERSION. BOUNDARY
LAYER WINDS ARE STRONG ENOUGH TO KEEP THE INVERSION ELEVATED THROUGH
THE REMAINDER OF THE EARLY MORNING HOURS...SO FOG SHOULD NOT BE A
CONCERN THIS MORNING.  THE LOW CEILINGS RANGING FROM 500 TO 1500
FEET SHOULD BEGIN TO LIFT TO AROUND 2500 TO 3500 FEET AFTER 14Z AS
THE INVERSION BEGINS TO WEAKEN AND MIX OUT.  IN GENERAL...THESE MVFR
AND VFR CEILINGS SHOULD PERSIST THROUGH THE REMAINDER OF THE DAY.
HOWEVER...THERE COULD ALSO BE SOME CONVECTIVE DEVELOPMENT AFTER
18Z...AS A STRONG UPPER LEVEL VORT MAX MOVES THROUGH.  GIVEN THE
HIGH PROBABILITY OF THUNDERSTORMS...HAVE VCTS WORDING IN PLACE AT
PRETTY MUCH ALL OF THE TERMINALS FOR THIS AFTERNOON AND EVENING. ANY
CONVECTION COULD EASILY PRODUCE BRIEF PERIODS OF STRONG WINDS AND
REDUCED VISIBILITIES IF PASSES OVER A TERMINAL. 32

MARINE...
THE PRESSURE GRADIENT OVER THE AREA WILL CONTINUE TO TIGHTEN TODAY
RESULTING IN STRONG ONSHORE FLOW OF 15 TO 25 KNOTS AND INCREASED
SEAS OF 4 TO 7 FEET. SMALL CRAFT ADVISORY FLAGS WILL TAKE HOLD OVER
THE OPEN GULF WATERS AND THE CHANDELEUR AND BRETON SOUNDS THIS
AFTERNOON AND THEN PERSIST THROUGH THURSDAY AFTERNOON. WINDS SHOULD
FALL TO AROUND 10 KNOTS AND SEAS SHOULD FALL TO 4 FEET OR LESS ON
FRIDAY AS A FRONT SLOWLY DRIFTS THROUGH THE COASTAL WATERS.  THE
FRONT IS EXPECTED TO FINALLY PUSH SOUTH OF THE REGION FRIDAY
NIGHT...ALLOWING A SURGE OF DRIER AND COOLER AIR TO OVERSPREAD THE
COASTAL WATERS.  OFFSHORE WINDS SHOULD INCREASE BACK INTO SMALL
CRAFT ADVISORY RANGE OF 20 TO 25 KNOTS AND SEAS SHOULD RISE BACK
INTO THE 4 TO 7 FEET RANGE OVER THE OPEN GULF WATERS LATE FRIDAY
NIGHT INTO SATURDAY.  AS HIGH PRESSURE SLOWLY SETTLES OVER THE
AREA...WINDS AND SEAS WILL DROP OFF SUNDAY INTO MONDAY.  BY MONDAY
AFTERNOON...LIGHT NORTHEAST FLOW OF 5 TO 10 KNOTS AND SEAS OF 1 TO 2
FEET ARE FORECAST FOR THE COASTAL WATERS AS THE SURFACE HIGH SETTLES
OVER THE GULF SOUTH. 32

DECISION SUPPORT...
DSS CODE....BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...MODERATE RIVER FLOODING.
             SMALL CRAFT ADVISORY CONDITIONS OFFSHORE.
             MONITORING SEVERE WEATHER AND HEAVY RAIN POTENTIAL FOR
             TODAY THROUGH FRIDAY.

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  76  68  78  61 /  50  70 100  80
BTR  79  69  80  64 /  60  70  70  70
ASD  76  69  79  66 /  40  60  70  70
MSY  78  70  81  67 /  40  50  50  60
GPT  75  69  76  68 /  30  60  70  80
PQL  75  69  79  69 /  20  40  60  80

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 5 PM CDT THURSDAY FOR GMZ536-538-550-
     552-555-557-570-572-575-577.

MS...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 5 PM CDT THURSDAY FOR GMZ538-550-552-
     555-557-570-572-575-577.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
458 AM CDT WED MAR 30 2016

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>082-302200-
LAKE PONTCHARTRAIN AND LAKE MAUREPAS-MISSISSIPPI SOUND-
LAKE BORGNE-CHANDELEUR SOUND-BRETON SOUND-
COASTAL WATERS FROM PORT FOURCHON LA TO LOWER ATCHAFALAYA RIVER
LA OUT 20 NM-
COASTAL WATERS FROM THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER
TO PORT FOURCHON LOUISIANA OUT 20 NM-
COASTAL WATERS FROM BOOTHVILLE LA TO SOUTHWEST PASS OF THE
MISSISSIPPI RIVER OUT 20 NM-
COASTAL WATERS FROM PASCAGOULA MISSISSIPPI TO STAKE ISLAND OUT
20 NM-
COASTAL WATERS FROM PORT FOURCHON LOUISIANA TO LOWER ATCHAFALAYA
RIVER LA FROM 20 TO 60 NM-
COASTAL WATERS FROM SOUTHWEST PASS OF THE MISSISSIPPI RIVER TO
PORT FOURCHON LOUISIANA FROM 20 TO 60 NM-
COASTAL WATERS FROM STAKE ISLAND LA TO SOUTHWEST PASS OF THE
MISSISSIPPI RIVER FROM 20 TO 60 NM-
COASTAL WATERS FROM PASCAGOULA MISSISSIPPI TO STAKE ISLAND
LOUISIANA OUT 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-
458 AM CDT WED MAR 30 2016

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

.DAY ONE...TODAY AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR AREAS NORTH OF
INTERSTATE 12 IN SOUTHEAST LOUISIANA INCLUDING METRO BATON ROUGE AND
ALL OF SOUTHWEST MISSISSIPPI. A MARGINAL RISK OF SEVERE
THUNDERSTORMS EXISTS ALONG THE INTERSTATE 10 CORRIDOR INCLUDING
METRO NEW ORLEANS AND THE MISSISSIPPI GULF COAST. THUNDERSTORMS
ARE MOST LIKELY FROM LATE AFTERNOON THROUGH THE OVERNIGHT HOURS.
THE PRIMARY THREATS FROM ANY SEVERE THUNDERSTORMS WILL BE HAIL AND
STRONG DAMAGING WIND GUSTS. A FEW TORNADOES MAY ALSO
DEVELOP...WITH THE HIGHEST RISK ACROSS SOUTHWEST MISSISSIPPI.

SMALL CRAFT ADVISORIES ARE IN EFFECT BEGINNING THIS AFTERNOON AND
PERSISTING INTO TONIGHT FOR ALL OF THE OPEN GULF WATERS AS WELL AS
THE CHANDELEUR AND BRETON SOUNDS. STRONG SOUTHERLY WINDS OF 20 TO
25 KNOTS AND SEAS OF 4 TO 7 FEET CAN BE EXPECTED.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE IS A SLIGHT TO ENHANCED RISK OF SEVERE THUNDERSTORMS FOR
AREAS ALONG AND NORTH OF THE INTERSTATE 10 CORRIDOR INCLUDING
METRO BATON ROUGE...METRO NEW ORLEANS...AND THE MISSISSIPPI GULF
COAST ON THURSDAY. A MARGINAL RISK OF SEVERE THUNDERSTORMS EXISTS
ACROSS COASTAL SOUTHEAST LOUISIANA. TORNADOES...LARGE HAIL...AND
STRONG DAMAGING WIND GUSTS WILL ALL BE POSSIBLE THREATS FROM ANY
SEVERE THUNDERSTORMS THAT FORM THURSDAY INTO THURSDAY NIGHT.

A MARGINAL TO SLIGHT RISK OF SEVERE THUNDERSTORMS WILL BE FOUND
ACROSS MOST OF THE AREA ON FRIDAY AS THE COLD FRONT MOVES
THROUGH. TORNADOES...HAIL...AND STRONG DAMAGING WIND GUSTS WILL
STILL BE A CONCERN WITH ANY SEVERE THUNDERSTORMS THAT FORM ON
FRIDAY.

SMALL CRAFT ADVISORY CONDITIONS WILL PERSIST THROUGH THURSDAY IN
ADVANCE OF THE APPROACHING COLD FRONT. STRONG ONSHORE FLOW OF 20
TO 25 KNOTS AND ROUGH SEAS OF 4 TO 7 FEET CAN BE EXPECTED.

ANOTHER ROUND OF SMALL CRAFT ADVISORY CONDITIONS WILL BE POSSIBLE
FRIDAY NIGHT INTO SATURDAY IN THE WAKE OF THE COLD FRONT. STRONG
NORTHERLY FLOW OF 20 TO 25 KNOTS AND SEAS OF 4 TO 7 FEET ARE
FORECAST.

WEATHER CAN CHANGE VERY RAPIDLY. ALWAYS USE THE LATEST
FORECASTS...WATCHES AND WARNINGS FOR PLANNING PURPOSES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED TODAY...TOMORROW...AND FRIDAY FOR
THE ENTIRE AREA DUE TO THREAT OF SEVERE THUNDERSTORMS.

32

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
336 PM CDT WED MAR 30 2016

LAZ034-035-302130-
WEST FELICIANA LA-POINTE COUPEE LA-
336 PM CDT WED MAR 30 2016

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN WEST FELICIANA AND
NORTHWESTERN POINTE COUPEE PARISHES UNTIL 430 PM CDT...

AT 335 PM CDT...DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR
BAYOU CURRENT...MOVING NORTH AT 25 MPH.

HALF INCH HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.

LOCATIONS IMPACTED INCLUDE...
BATCHELOR AND LETTSWORTH.

LAT...LON 3087 9180 3098 9180 3099 9178 3100 9178
      3104 9172 3104 9165 3097 9166 3100 9164
      3099 9149 3063 9171 3064 9175 3067 9173
      3071 9173 3078 9176 3081 9181 3084 9180
      3086 9182
TIME...MOT...LOC 2035Z 197DEG 20KT 3074 9179