Heavy Rain Threat - Week of 4/12/15

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
359 PM CDT SUN APR 12 2015

.SHORT TERM...
ACTIVE/WET WEATHER WILL CONTINUE THROUGH MUCH IF NOT ALL OF THE
WEEK AS MULTIPLE MID/UPPER LEVEL DISTURBANCES ROTATE THROUGH THE
AREA AROUND OVERALL UPPER LEVEL TROUGHING.

HIGH CONFIDENCE THAT MULTIPLE ROUNDS OF RAINFALL...HEAVY AT
TIMES...WILL AFFECT THE AREA AT LEAST THROUGH THE NEXT FEW DAYS.
HAVE LOWER CONFIDENCE IN EXACT AMOUNTS AND LOCATIONS OF HIGHEST
RAINFALL TOTALS. AREA AVERAGE QPF IS CURRENTLY FORECAST IN THE 2
TO 4 INCH RANGE THROUGH TUESDAY WITH LOCALLY HIGHER AMOUNTS
POSSIBLE.

HAVE GONE AHEAD AND HOISTED A FLASH FLOOD WATCH FOR PORTIONS OF
THE AREA GENERALLY ALONG AND SOUTH OF A LINE FROM GROSSE TETE TO
LAPLACE TO NEW ORLEANS. RADAR ESTIMATES INDICATE AREAS TO THE
SOUTHWEST OF LAKE PONTCHARTRAIN HAVE ALREADY ACCUMULATED 3 TO 6
INCHES OF RAIN OVER THE PAST 24 TO 48 HOURS. THOUGH WE HAVE NO
ACTUAL OBSERVATIONS IN THE HEAVIEST RAINFALL AREAS...THE
OBSERVATIONS WE DO HAVE LINE UP FAIRLY WELL WITH THE ESTIMATES...
SO THE 3 TO 6 INCHES PROBABLY ISN/T TOO FAR OFF. ADDITIONALLY...A
LARGE SHIELD OF PRECIP OVER THE GULF MOVING INLAND OVER SOUTH
CENTRAL AND SOUTHEAST LA. THOUGH THERE IS LITTLE HEAVY CONVECTION
EMBEDDED WITHIN THAT PRECIP SHIELD...IT WILL BRING A DECENT AMOUNT
OF LIGHT TO MODERATE RAINFALL TO AREAS WHERE THE GROUND IS ALREADY
CLOSE TO SATURATED IF NOT ALREADY SATURATED. THIS WILL IN TURN
FURTHER REDUCE THE AMOUNT OF FUTURE RAINFALL NECESSARY TO
PRODUCE FLASH FLOODING. WHILE NOLA METRO HAS NOT RECEIVED AS MUCH
RAINFALL TO DATE...WITH THE MANY URBANIZED AREAS IN THOSE
PARISHES...IT DOESN/T TAKE AS MUCH RAINFALL TO RESULT IN
FLOODING...SO WILL GO AHEAD AND INCLUDE JEFFERSON...ORLEANS...
PLAQUEMINES AND ST BERNARD PARISHES IN THE WATCH AS WELL. WILL
CARRY THE WATCH THROUGH 00Z TUESDAY FOR THE TIME BEING...KNOWING
THAT IT MAY NEED TO BE EXPANDED IN TIME...AREA...OR BOTH
DEPENDING ON HOW THINGS PLAY OUT TONIGHT AND MONDAY.

HIGH RAIN CHANCES CONTINUE INTO AT LEAST MIDWEEK AS SOUTHWEST
FLOW ALOFT CONTINUES TO USHER FAST MOVING DISTURBANCES THROUGH THE
LOWER MISSISSIPPI VALLEY. AM CARRYING LIKELY TO DEFINITE POPS
FOR EACH PERIOD THROUGH WEDNESDAY. EXACT QPF WILL BE HIGHLY
DEPENDENT ON WHERE HEAVIEST RAINFALL SETS UP EACH DAY. FOR NOW AM
CARRYING AVERAGES OF 1 TO 2 INCHES EACH DAY...BUT LOCAL AMOUNTS
COULD BE SIGNIFICANTLY HIGHER AS PW VALUES OF 1.5 TO 2.0 INCHES
WILL ALLOW FOR EFFICIENT RAINFALL PRODUCTION FROM ANY
THUNDERSTORMS.

.LONG TERM...
BY THURSDAY...BULK OF DEEP MOISTURE BEGINS TO SHIFT EASTWARD. THUS
AM CARRYING LOWER...ONLY RELATIVELY SPEAKING...POPS IN THE THE
CHANCE RANGE.

FORECAST CONFIDENCE GOING INTO THE WEEKEND IS VERY LOW. WITH
LITTLE EXCEPTION...THERE ARE MASSIVE INCONSISTENCIES BETWEEN THE
DIFFERENT MODELS. THE ONLY THING THEY SEEM TO AGREE ON IS THAT
THEY HAVE GENERALLY ALL PERSISTENTLY BEEN SLOWING THE DRYING
FRONT WITH EVERY MODEL RUN FOR THE LAST SEVERAL CYCLES. THAT BEING
SAID...ACTIVE WEATHER PATTERN COULD CONTINUE THROUGH THE
WEEKEND AND THE FORECAST HAS BEEN ADJUSTED TO ACCOUNT FOR THIS
POSSIBILITY. EVEN IF THE FRONT MANAGES TO MAKE IT THROUGH...EXPECT
TEMPS TO COOL ONLY TO NEAR NORMAL FROM THE ABOVE NORMAL TEMPS THAT
HAVE BEEN THE RULE LATELY.

&&

.AVIATION...
CHALLENGING FORECAST DUE TO HIGHLY VARIABLE CIG/VSBY CONDITIONS
BOTH IN AND OUT OF THE RAIN AREAS...AND THE USUAL PROBLEM WITH
FORECASTING THE TIMING AND PLACEMENT OF TSRA. REDEVELOPMENT OF
RA/SHRA ALONG/NORTH OF INTERSTATE 10 WEST OF LAKE PONTCHARTRAIN
AND ADVANCING AREA OF RAIN AND TSRA IN THE GULF OF MEXICO
SOUTHWEST OF KHUM WILL EVENTUALLY LEAD TO MORE WIDESPREAD RAIN AND
SHRA BY LATE AFTERNOON AND EVENING. THIS SHOULD LEAD TO MORE AREAS
OF MVFR TO IFR CONDITIONS AS THE EVENING PROGRESSES.

&&

.MARINE...
TIGHTENING PRESSURE GRADIENT BETWEEN BROAD LOW PRESSURE TO THE
NORTHWEST AND HIGH PRESSURE OVER THE EASTERN CONUS WILL LEAD TO
MODERATE OR EVEN TEMPORARY STRONG ONSHORE FLOW AT TIMES THROUGH
THE NEXT FEW DAYS. ONSHORE FLOW WILL CONTINUE THROUGH THE WORK
WEEK AND COULD RESULT IN ABOVE NORMAL TIDES DEPENDING ON THE
STRENGTH OF THE WINDS. ADDITIONALLY...SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO AFFECT THE COASTAL
WATERS THROUGH THE WEEK...WITH STRONGER WINDS AND ROUGHER SEAS IN
AND AROUND ANY THUNDERSTORMS.

&&

.DECISION SUPPORT...
DSS CODE...BLUE.
DEPLOYED...METS TO AVONDALE AND NEW ORLEANS COMMAND CENTER
ACTIVATION...YES.
ACTIVITIES...FRENCH QUARTER FEST PUBLIC SAFETY SUPPORT
GRAND PRIX OF LOUISIANA PUBLIC SAFETY SUPPORT
FLASH FLOOD WATCH FOR AREAS GENERALLY SOUTH AND
WEST OF LAKE PONTCHARTRAIN AND MAUREPAS.


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 TONIGHT RISK SVR
AND/OR DIRECT TROPICAL THREATS; EVENTS OF NATIONAL
SIGNIFICANCE

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB 76 66 78 66 / 70 70 80 50
BTR 77 68 80 68 / 80 70 80 50
ASD 78 69 80 69 / 70 70 80 50
MSY 76 70 80 70 / 70 60 80 50
GPT 74 70 78 71 / 70 70 80 40
PQL 77 70 79 71 / 70 70 80 40

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...FLASH FLOOD WATCH THROUGH MONDAY EVENING FOR LAZ046-049-056>070.

GM...NONE.
MS...NONE.
GM...NONE.
&&

$$

.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
446 PM CDT SUN APR 12 2015

.DISCUSSION...
WIDESPREAD RAIN WITH EMBEDDED HEAVIER SHOWERS AND ISOLATED
THUNDERSTORMS UNDERWAY ACROSS THE AREA THIS AFTERNOON.

A VERY MOIST AIRMASS IS CURRENTLY IN PLACE ACROSS THE REGION...WITH
THE PWAT ON THE MORNING KLCH RAOB A VERY JUICY 1.95 INCHES...WHICH
IS QUITE NEAR THE ALL TIME MAX FOR APRIL. THIS POOL OF RICH MSTR
IS PROGGED TO REMAIN WITH US THROUGH AT LEAST MONDAY...WHILE
SUBTLE DISTURBANCES TRANSLATE THROUGH THE WEST TO SOUTHWEST FLOW
ALOFT DOWNSTREAM OF A SLOWLY EASTWARD MOVING UPPER TROF.

LATEST PROGS SUGGEST THE CURRENT ACTIVITY SHOULD BE SLOW TO WIND
DOWN THIS EVENING...MUCH LIKE LAST NIGHT...BUT EVENTUALLY SHOULD
END AND PROVIDE A BIT OF A BREAK DURING THE LATE EVENING AND
OVERNIGHT HOURS BEFORE THE NEXT ROUND BEGINS TO DEVELOP/MOVE INTO
THE AREA EARLY MONDAY. CONFIDENCE IS NOT HIGH REGARDING THE EXACT
EVOLUTION...BUT THE OVERALL PATTERN REMAINS SIMILAR TO IF NOT A
LITTLE BETTER THAN TODAY FOR FAIRLY WIDESPREAD RAINFALL ALONG WITH
AT LEAST LOCALLY HEAVY RAINFALL. GIVEN THE ANTECEDENT CONDITIONS
SETUP BY SEVERAL PERIODS OF RAIN RESULTING IN A GOOD SWATH OF 1-3
INCHES AND POCKETS OF 4-6...HAVE ISSUED A FLASH FLOOD WATCH FOR
SE TX/SRN LA FOR THE REST OF TODAY THROUGH MONDAY.

ACTIVE SOUTHWESTERLY JET AMID A RELATIVELY MOIST AIRMASS IS
PROGGED TO PERSIST THROUGH THE END OF THE WEEK AND AT LEAST INTO
THE WEEKEND...HOLDING THE CLOUDY/WET PATTERN IN PLACE.

Heavy rain is developing across the metro. The ground is saturated and we should pay close attention for flooding.