Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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856
FXUS64 KLIX 182153
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
353 PM CST THU DEC 18 2014

.DISCUSSION...
WEATHER WILL BE FAIRLY ACTIVE THROUGH THE PERIOD WITH MULTIPLE
DISTURBANCES IMPACTING THE AREA.

MAIN FORECAST CHALLENGE CONCERNS IMPACTS FROM THE SURFACE LOW
FORECAST TO MOVE THROUGH THE AREA LATE FRIDAY/EARLY SATURDAY. MAIN
CHANGE FROM THIS MORNING/S FORECAST IS AN INCREASE IN POPS FOR
TONIGHT AND FRIDAY. IN FACT...AM CARRYING 100 PERCENT POPS FOR
ROUGHLY THE NORTHWEST THIRD OF THE FORECAST AREA ON FRIDAY DUE TO
HIGH CONFIDENCE THAT WE WILL SEE WIDESPREAD SHOWERS AS THE LOW
APPROACHES THE AREA. HAVE ALSO BUMPED UP RAINFALL TOTALS A BIT
BASED ON LATEST GUIDANCE. THOUGH THERE IS STILL SOME UNCERTAINTY
CONCERNING WHERE THE HEAVIEST RAIN WILL OCCUR...WE ARE FAIRLY
CONFIDENT THAT RAINFALL TOTALS WILL BE IN THE 1 TO 3 INCH RANGE
FOR MANY PLACES.

HPC IS HIGHLIGHTING AT LEAST SOME RISK OF EXCESSIVE RAINFALL...
I.E. RAINFALL THAT EXCEEDS FLASH FLOOD GUIDANCE...ACROSS PORTIONS
OF THE AREA ON FRIDAY. PRECIPITABLE WATER VALUES ARE FORECAST TO
BE BETWEEN 1.25 AND 1.5 INCHES...WHICH IS WELL ABOVE NORMAL FOR
THIS TIME OF YEAR AND WOULD CERTAINLY SUPPORT SOME EFFICIENT
RAINFALL RATES. THE LIMITING FACTOR WILL COME DOWN TO A LACK OF
INSTABILITY TO SUPPORT STRONGER THUNDERSTORMS. RIVERS AND OTHER
RESERVOIRS ARE LOW ENOUGH THAT WIDESPREAD FLOODING OR FLASH
FLOODING SHOULD NOT BE AN ISSUE. WITH THAT SAID HOWEVER...IF A
SPECIFIC LOCATION DOES HAPPEN TO EXPERIENCE A COUPLE ROUNDS OF
HEAVIER RAIN...WE COULD SEE SOME NUISANCE TYPE FLOODING OF
ROADWAYS...LOW LYING AREAS AND POOR DRAINAGE AREAS. BECAUSE THE
THREAT DOES APPEAR TO BE ISOLATED AT THIS TIME...WILL FORGO ANY
KIND OF WATCH PRODUCT WITH THIS PACKAGE.

ONTO THE RISK OF SEVERE WEATHER...MODELS CONTINUE TO COME INTO
AGREEMENT THAT THE SURFACE LOW WILL PASS THROUGH THE AREA NEAR THE
COAST. A TRACK THIS FAR SOUTH WILL KEEP THE MORE UNSTABLE AIR OVER
THE GULF WITH ONLY VERY MARGINAL AND ELEVATED INSTABILITY
AVAILABLE OVER LAND AREAS. WITH THE CURRENT FORECAST TRACK...ANY
STRONG/SEVERE THUNDERSTORMS SHOULD BE LIMITED TO COASTAL AREAS OF
SOUTHEAST LOUISIANA...AND SPC/S LATEST OUTLOOK AGREES WITH THIS
LINE OF THINKING AS THEY CONTINUE TO WHITTLE AWAY NORTHERN PARTS
OF THEIR MARGINAL RISK AREA. SINCE THERE IS AT LEAST SOME ELEVATED
INSTABILITY OVER LAND AREAS...WILL GO AHEAD AND MAINTAIN A SLIGHT
CHANCE OF THUNDER FOR FRIDAY.

THE LOW WILL ELONGATE AND WEAKEN AS IT MOVES EAST/NORTHEAST AWAY
FROM THE AREA AND ITS ASSOCIATED COLD FRONT IS EXPECTED TO STALL
OVER THE NORTHERN GULF AS THE UPPER TROUGH LIFTS NORTHEASTWARD
AND WINDS BECOME MORE PARALLEL TO THE FRONT. THIS WILL RESULT IN
CONTINUED CLOUD COVER AND SOME SPOTTY LIGHT SHOWERS LINGERING
THROUGH THE WEEKEND...ESPECIALLY ON SUNDAY AS THE FRONT BEGINS TO
MOVE NORTHWARD IN RESPONSE TO ANOTHER DEVELOPING WEAK LOW PRESSURE
OVER THE WESTERN GULF.

THIS SECOND SURFACE LOW IS EXPECTED TO REMAIN OVER THE GULF AS IT
PASSES BY...SO SEVERE WEATHER IS NOT A THREAT...AND EVEN GETTING
THUNDERSTORMS TO DEVELOP WILL BE A STRETCH. AS THIS LOW PASSES THE
AREA SUNDAY NIGHT AND MONDAY...EXPECT ISOLATED TO SCATTERED
SHOWERS TO MOVE THROUGH THE AREA.

A THIRD UPPER TROUGH WILL FINALLY FORCE A CLEARING COLD FRONT
THROUGH THE AREA ON TUESDAY. THIS WILL BRING YET ANOTHER CHANCE
OF RAIN TO THE REGION. INSTABILITY WILL ONCE AGAIN BE
LIMITED...HOWEVER...AND THUNDERSTORMS WILL BE HARD TO COME BY.
THIS FRONT IS FORECAST TO MAKE IT WELL INTO THE GULF...WITH CLOUDS
CLEARING BEHIND IT AND NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES
FORECAST FOR CHRISTMAS EVE AND CHRISTMAS DAY.

&&

.AVIATION...
NOT MUCH CHANGE IN THE FORECAST THINKING FROM PREVIOUS FORECASTS
WITH WEAK SURFACE LOW MOVING FROM TX COAST THRU SOUTH LA LATE
TONIGHT THROUGH EARLY SAT. MVFR CIGS SHOULD BECOME WIDESPREAD
TONIGHT AS WARMER AIR SPREADS NORTHWARD IN THE BOUNDARY LAYERS.
SOME IFR CIGS AND VIS IN RAIN AND SHOWERS POSSIBLE...ESPECIALLY
AFTER 06Z. WIDESPREAD LOW MVFR CIGS AND VIS IN RAIN AND FOG WITH
OCCASIONAL IFR CIGS LIKELY MOST TERMINALS AFTER 12Z. ISOLATED TSRA
CAN NOT BE RULED OUT AFTER 09Z THROUGH 18Z.

&&

.MARINE...
AS A LOW PRESSURE SYSTEM FORMS ALONG THE TEXAS COAST AND
APPROACHES THE LOCAL WATERS FRIDAY...WINDS WILL BECOME MORE
SOUTHEAST AND INCREASE TO NEAR 15 KNOTS WITH SEAS 3 TO 5 FEET.
SMALL CRAFT EXERCISE CAUTION HEADLINES MAY BE NECESSARY FOR AT
LEAST A SHORT PERIOD OF TIME AHEAD OF THE LOW ON FRIDAY. THERE
WILL BE AT LEAST SOME POTENTIAL FOR THUNDERSTORMS OVER THE COASTAL
WATERS ON FRIDAY...AND ONE OR TWO COULD BE STRONG...PRODUCING GALE
FORCE WIND GUSTS AND LOCALLY ROUGH SEAS. THE LOW WILL ELONGATE AND
WEAKEN AS IT PASSES THE AREA LATE FRIDAY/EARLY SATURDAY...WITH A
WEAK FRONTAL BOUNDARY STALLING OVER THE NORTHERN GULF. THIS WILL
KEEP CONDITIONS GENERALLY CLOUDY WITH LINGERING SHOWERS THROUGH
THE WEEKEND AND INTO MONDAY. GOING INTO TUESDAY...A STRONGER COLD
FRONT WILL FINALLY CLEAR THE AREA. STRONG WINDS AND ROUGH SEAS
BEHIND THIS FRONT WILL LIKELY NECESSITATE SMALL CRAFT ADVISORIES.

&&

.DECISION SUPPORT...
DSS CODE...GREEN.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT.

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 TO HIGH RISK SVR
         AND/OR DIRECT TROPICAL THREATS; EVENTS OF NATIONAL
         SIGNIFICANCE.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  47  52  44  58 /  50 100  70  20
BTR  51  60  46  61 /  60 100  60  20
ASD  49  58  47  61 /  40  90  70  20
MSY  55  63  52  61 /  40  90  60  20
GPT  48  57  49  61 /  30  80  70  30
PQL  43  58  44  63 /  30  70  70  30

&&

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

$$

AVIATION...21
REST OF DISCUSSION...95/DM





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