Flash Flood Warning 18, NWS New Orleans, LA

AREA FORECAST DISSCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
433 AM CST SAT MAR 12 2016

.SYNOPSIS...

MUCH QUIETER MORNING THAN IT WAS 24 HOURS AGO. STACKED LOW
PRESSURE OVER TEXAS HAS FINALLY TAKEN ON A BIT OF NEGATIVE TILT
THIS MORNING AND APPEARS TO BE MAKING AT LEAST A BIT OF PROGRESS.
STILL QUITE A BIT OF CONVECTION IN THE CENTRAL GULF OF
MEXICO...BUT THE DIFFERENCE THIS MORNING IS THAT THE HEAVIEST
CONVECTION DOES NOT APPEAR TO BE MAKING A BEELINE FOR THE
LOUISIANA COAST. SHOWING MORE OF AN EASTWARD DRIFT THAN A
NORTHWARD MOVEMENT. STILL SEEING A BIT OF OUTFLOW FROM CONVECTION
TO THE EAST OVER PORTIONS OF THE MISSISSIPPI COAST WITH A GUST TO
30 KNOTS AT PASCAGOULA IN THE LAST HOUR. MOISTURE LEVELS ARE DOWN
A BIT WITH DEW POINTS ONLY IN THE LOWER AND MID 60S THIS MORNING.
TEMPERATURES ARE IN THE 60S AS WELL.

&&

.SHORT TERM...

MAIN CONCERN IS RAIN THREAT IN THE FIRST 18 HOURS OF THE FORECAST.
MOISTURE LEVELS HAVE TEMPORARILY DROPPED TO AROUND 1.2 INCHES PER
00Z LIX SOUNDING AND SOUNDER DATA...BUT SOUNDER IMAGERY SHOWS
HIGHER MOISTURE LEVELS JUST OFF THE COAST. UPPER LOW FORECAST TO
OPEN UP AND LIFT TO NEAR MEMPHIS BY SUNDAY MORNING...WITH A SECOND
SHORTWAVE ON ITS HEELS OVER THE TEXAS/OKLAHOMA PANHANDLES.
CURRENTLY APPEARS THAT CONVECTION OVER THE GULF MAY STAY JUST EAST
OF THE AREA PER MESOSCALE MODELS...BUT SCATTERED CONVECTION LIKELY
TO DEVELOP NEAR THE UPPER LOW TRACK. RAIN AMOUNTS ASSOCIATED WITH
THE UPPER LOW LOOK TO BE ABOUT AN INCH...BUT IN MUCH OF THE
AREA...IT WILL NOT TAKE MUCH MORE THAN THAT TO CAUSE OR AGGRAVATE
FLOODING PROBLEMS. PATH OF LEAST REGRET IS TO LEAVE FLASH FLOOD
WATCH IN PLACE UNTIL EXPIRATION AT 00Z. EXPECT TO SEE SIGNIFICANT
DRYING OF THE AIRMASS AFTER MIDNIGHT...NOT LEAVING MUCH MOISTURE
FOR THE SECOND SHORTWAVE TO WORK WITH AS IT PASSES NORTH OF THE
AREA SUNDAY NIGHT. THIS SHOULD KEEP THE AREA DRY THROUGH
TUESDAY...ALLOWING TIME FOR SOME OR MOST OF THE RIVERS TO RETURN
TO WITHIN THEIR BANKS.

CLOUD COVER SHOULD HOLD TEMPERATURES IN THE LOW AND MID 70S FOR
HIGHS TODAY. WILL TREND BELOW THE WARM END OF THE GUIDANCE
ENVELOPE FOR HIGHS MONDAY AND TUESDAY WITH THE GROUND BEING
EXTREMELY WET. THIS SHOULD ALSO HOLD LOW TEMPERATURES TOWARD THE
WARMER END OF THAT ENVELOPE. 35

&&

.LONG TERM...

MEDIUM RANGE MODELS CONTINUE TO HAVE SIGNIFICANT DIFFERENCES IN
SOLUTIONS FROM WEDNESDAY ONWARD. ABOUT THE ONLY THING THEY AGREE
ON IS A STRONG UPPER SYSTEM MOVING THROUGH THE GREAT LAKES STATES
AT MIDWEEK. THIS WILL PUSH A FRONT INTO THE AREA ON
WEDNESDAY...BUT THE FRONT MAY NOT MAKE IT MUCH FURTHER SOUTHWARD.
COOLER AIR WITH THIS SYSTEM...BUT THE QUESTION IS THE MAGNITUDE OF
THE COLD AIR PUSH. WILL TREND TOWARD THE SOMEWHAT WETTER ECMWF
GUIDANCE ON RAIN CHANCES...AND TAKE A BLENDED APPROACH ON
TEMPERATURES UNTIL DIFFERENCES RESOLVE. 35

&&

.AVIATION...

CONDITIONS WERE BECOMING MOSTLY MVFR WITH A COUPLE AIRPORTS TEMPO TO
PREVAILING IFR DUE TO A COMBINATION OF CIGS AND VSBYS IN PATCHY
LIGHT RAIN. A FEW MORE AIRPORTS MAY TREND DOWN TOWARDS IFR THROUGH
12-15Z. SHRA/TSRA OVER THE WEST CENTRAL TO NORTH CENTRAL GULF ARE
EXPECTED TO MOVE NORTH AND NORTHEAST INTO SECTIONS OF THE FORECAST
AREA THIS MORNING. THE THREAT OF SHOWERS AND A FEW THUNDERSTORMS
WILL CONTINUE THROUGH MUCH OF THE DAY...ALTHOUGH THE THREAT WILL
GRADUALLY SHIFT EASTWARD DURING THE COURSE OF THE AFTERNOON. 22/TD

&&

.MARINE...

A COMBINATION OF STRONGER SOUTHEAST WINDS AND SEAS UP TO 7 FEET IS
EXPECTED TO KEEP SMALL CRAFT ADVISORY CONDITIONS ACROSS MOST OF THE
COASTAL WATERS THROUGH THIS AFTERNOON. THE STRONGER SOUTHEAST WIND
ARE DUE TO THE LOW PRESSURE SYSTEM APPROACHING FROM THE WEST AND A
HIGH PRESSURE RIDGE OVER THE EASTERN GULF COAST. CONDITIONS WILL BE
IMPROVING FROM THE WEST LATE THIS AFTERNOON AS THE PRESSURE GRADIENT
RELAXES TONIGHT. A LOW PRESSURE SYSTEM WILL MOVE ACROSS THE SOUTHERN
PLAINS AND MID MISSISSIPPI VALLEY SUNDAY AND SUNDAY NIGHT WHICH
SHOULD CAUSE SOUTHWEST WINDS TO RISE BACK TO AROUND 15 KNOTS ACROSS
THE COASTAL WATERS. THE PRESSURE GRADIENT SHOULD THEN RELAX AGAIN
WITH WINDS EASING LATE TUESDAY NIGHT INTO WEDNESDAY AS A SLOW MOVING
COLD FRONT APPROACHES. 22/TD

&&

.DECISION SUPPORT...

DSS CODE....ORANGE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...COASTAL FLOODING
             FLASH FLOODING
             MAJOR RIVER FLOODING

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  72  58  76  60 /  90  30  10  10
BTR  75  59  78  62 /  70  20  10  10
ASD  74  61  76  62 /  90  30  10  10
MSY  74  62  77  64 /  80  20  10  10
GPT  71  62  73  62 /  90  40  10  10
PQL  71  62  74  62 /  90  40  10  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...FLASH FLOOD WATCH THROUGH THIS AFTERNOON FOR LAZ034>037-039-040-
     046>050-056>072.

     COASTAL FLOOD ADVISORY UNTIL 6 PM CST THIS EVENING FOR LAZ057-
     060>064-066>070.

     COASTAL FLOOD WARNING UNTIL 6 PM CST THIS EVENING FOR LAZ040-049-
     050-058-072.

GM...SMALL CRAFT ADVISORY UNTIL 6 PM CST THIS EVENING FOR GMZ532-536-
     538-555-557-570-572-575-577.

MS...FLASH FLOOD WATCH THROUGH THIS AFTERNOON FOR MSZ068>071-077-
     080>082.

     COASTAL FLOOD ADVISORY UNTIL 6 PM CST THIS EVENING FOR MSZ081-
     082.

     COASTAL FLOOD WARNING UNTIL 6 PM CST THIS EVENING FOR MSZ080.

GM...SMALL CRAFT ADVISORY UNTIL 6 PM CST THIS EVENING FOR GMZ536-538-
     555-557-570-572-575-577.

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE NEW ORLEANS LA
313 PM CST SAT MAR 12 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>082-130915-
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-
313 PM CST SAT MAR 12 2016

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

A FLASH FLOOD WATCH REMAINS IN EFFECT UNTIL 6 PM...EXCLUDING PARTS
OF COASTAL MISSISSIPPI. ADDITIONAL RAINFALL OF 1 INCH WITH
LOCALLY HIGHER AMOUNTS IS POSSIBLE BEFORE THE LOW PRESSURE MOVES
NORTHEAST OF THE AREA THIS EVENING.

COASTAL FLOOD WARNINGS AND ADVISORIES REMAIN IN EFFECT THROUGH 7
AM SUNDAY MORNING.

NUMEROUS RIVERS ARE IN FLOOD ACROSS SOUTHEAST LOUISIANA AND
SOUTHERN MISSISSIPPI. FOR DETAILED INFORMATION CONSULT THE LATEST
FLOOD WARNINGS AND FLOOD STATEMENTS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

RIVER FLOODING IS EXPECTED TO CONTINUE. FOR DETAILED INFORMATION
CONSULT THE LATEST FLOOD STATEMENTS AND WARNINGS.

OTHERWISE THE THREAT OF HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NECESSARY TODAY...MAINLY FOR FLOOD
REPORTING.