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

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299
FXUS64 KLIX 191802
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1202 PM CST FRI DEC 19 2014

.AVIATION...
MAIN FORECAST PROBLEM AND LACK OF CONFIDENCE IS REGARDING THE
TIMING OF THE LOWER LIFR CATEGORY CIGS AND IFR VSBYS THAT WILL
MAINLY BE ASSOCIATED WITH THE MORE PERSISTENT AND HEAVIER SHRA
AND ISOLATED TSRA. HAVE TRIED TO TIME THIS IN THE SHORT TERM WITH
OBSERVATIONS...RADAR TRENDS...AND WRF/HRRR MODELS.
OVERALL...CONDITIONS WILL TREND TOWARDS IFR AND LIFR THROUGH
EARLY SATURDAY MORNING WITH SLOW IMPROVEMENT EXPECTED LATER
SATURDAY MORNING AS THE RAIN SHOULD MOSTLY END FROM WEST TO EAST.
22/TD

&&

.PREV DISCUSSION... /ISSUED 404 AM CST FRI DEC 19 2014/

SYNOPSIS...
THREE SYSTEMS TO WATCH AS AN ACTIVE PATTERN IS UNDERWAY THROUGH
THE MIDDLE OF NEXT WEEK. ROUND ONE IS A SHORT WAVE AND LOW
PRESSURE CENTER OR OPEN WAVE MOVING FROM TX TO THE LA COAST TODAY
AND TONIGHT. ROUND TWO WILL BE A CHANCE OF RAIN ASSOCIATED WITH A
WARM FRONTAL BOUNDARY MOVING NORTH FROM THE GULF ASSOCIATED WITH
THE NEXT MUCH MORE SYNOPTICALLY VIGOROUS ROUND 3 SYSTEM WHICH WILL
SWEEP A COLD FRONT INTO THE COASTAL WATERS ON TUESDAY. KEG

SHORT TERM...
ROUND ONE RAIN IS KNOCKING AT OUR DOOR THIS MORNING AS A SHORT
WAVE APPROACHES WITH AN ASSOCIATED LOW PRESSURE DEVELOPING ON A
WARM FRONT. PW UP TO 1.38 ON 00Z SOUNDING. SATL ESTIMATES PW
VALUES UP TO 1.6 INCHES NOW. DID AN OLD FASHIONED HAND ANALYSIS
THIS MORNING WITH PAPER AND A REAL PENCIL... CYCLOGENISIS UNDERWAY
WITH A LOW CURRENTLY OVER KCRP. RAIN ASSOCIATED WITH THIS SYSTEM
IN TEXAS AND SW LA OVERNIGHT WITH A FEW LIGHTNING STRIKES SHOWING
UP THIS MORNING. SOME SMALL HAIL REPORTS IN TEXAS WHERE LAPSE
RATES WERE MORE SUPPORTIVE. MAIN IMPACT FROM THIS FIRST SYSTEM
WILL BE RAIN AS THE CURRENT TRACK OF THE LOW STAYS ALONG THE COAST
KEEPING THE MOST UNSTABLE AIR WELL IN THE GULF. 600-800 J/KG CAPE
IN THE GULF AT 18Z WITH ANY SIGNIFICANT SHEAR OUT PACING THE RAIN
TODAY. WITH WEAK INSTABILITY SEVERE CHANCES SHOULD BE LOW. EXPECT
TO SEE SOME ELEVATED THUNDERSTORMS TODAY AND WITH ADDED
ISCENTROPIC LIFT SOME AREAS OF HEAVY RAIN CAN BE EXPECTED. HPC
ANALYSIS LOOKS GOOD WITH A 1 TO 3 INCH QPF SWATH WELL NORTH OF THE
LOW WHERE RAIN WILL BE MOST EFFICIENT. IMPACT SHOULD BE LOW AS THE
RIVERS ARE LOW AND THE SOIL IS DRY. THERE IS A MARGINAL RISK OF
SEVERE WEATHER TODAY WITH SOME THREAT OF A HIGH WINDS AND ELEVATED
MESOS. THE SYSTEM SHOULD MOVE OUT BY NOON SATURDAY. KEG

LONG TERM...
ROUND TWO IS ON SUNDAY AS A DEEPENING SHORT WAVE IN THE MID WEST
FORCES A WARM FRONTAL BOUNDARY NORTH. SOME SHOWERS WILL DEVELOP
ON THE FRONT MAINLY IMPACTING THE COAST...SE LA AND MS GULF COAST.
LOOKS LIKE MOST OF THE INSTABILITY WILL BE OFFSHORE AGAIN WITH
THIS SYSTEM LIMITING CHANCES FOR SEVERE WEATHER.

A PATTERN CHANGE FOR THE ECONUS COMES NEXT CREATING OUR ROUND 3
EVENT WHICH WILL CLEAR OUT THE MOISTURE. A DEEPENING LOW BOTTOMS
OUT AROUND CRESCO IOWA AT 06Z TUE PER THE GFS. THE TROUGH DIGS
SOUTH AS THE LOW MOVES NORTH AND CENTERS OVER NEW RICHMOND
WISCONSIN BY 18Z TUE AND STRENGTHENS A BAROCLINIC ZONE. A COLD
FRONT WILL PUSH THROUGH TUE AND BRING ANOTHER CHANCE FOR RAIN. THE
ECMWF IS MORE AGGRESSIVE WITH THE RAIN CHANCES THAN THE GFS BUT
BOTH AGREE THE HIGHER AMOUNTS ARE OFFSHORE. 600 J/KG CAPE AHEAD
OF THE FRONT WITH VERY LITTLE SHEAR. THERE IS WEAK INSTABILITY
FORCED ALONG THE FRONT BUT IT DOES NOT APPEAR TO SUPPORT
WIDESPREAD SEVERE WEATHER. COOLER TEMPERATURES TO FOLLOW AS A
HIGH PRESSURE CENTERS OVER DEEP SOUTH TEXAS. THE HIGH MOVES
QUICKLY EAST BRINGING SOUTHERLY FLOW BACK TO OUR FORECAST AREA.
FOR THE 24TH AND 25TH SKIES WILL BE MOSTLY CLEAR...NIGHTS COOL...
AND TEMPERATURES IN THE UPPER 60S. COULD SEE LOWER 70S IN SOME
AREAS BY THE 26TH. KEG

AVIATION...
MUCH OF THE NEXT 24 HOURS WILL BE DOMINATED BY LOW END MVFR TO IFR CIGS
AND...AT TIMES...IFR VSBY IN HEAVY SHRA/ISOLATED TSRA WITH GULF LOW
TRANSITING THE COAST THROUGH TONIGHT. CONDITIONS WILL BE LOWER AT WESTERN
TERMINALS INITIALLY THEN SPREADING EASTWARD THROUGH THE LATE MORNING HOURS.
NOT ANTICIPATING ANY APPRECIABLE IMPROVEMENTS UNTIL SHORTLY AFTER THIS
TAF VALID PERIOD...GENERALLY AFTER 20/15Z. 24/RR

MARINE...
A SHORT WAVE AND LOW PRESSURE ALONG A WARM FRONT WILL MOVE THROUGH
THE COASTAL WATERS TODAY. EACH MODEL RUN HAS MOVED THE TRACK OF
THE LOW FURTHER SOUTH AND IF WEAK ENOUGH WILL JUST BE AN OPEN
WAVE. SHOWERS AND THUNDERSTORMS ARE LIKELY AS THE LOW TRACKS
EAST...SOME OF THE STORMS COULD BE STRONG WITH GALE FORCE GUSTS
AND LOCALLY ROUGH SEAS. THE LOW WILL MOVE OUT SATURDAY KEEPING AN
OLD FRONTAL BOUNDARY IN THE OFFSHORE WATERS. A TROUGH OF LOW
PRESSURE DIGS SOUTH FORCING THE WARM FRONT NORTH ON SUNDAY. THIS
WILL BRING ANOTHER CHANCE FOR RAIN AND A FEW THUNDERSTORMS SUNDAY
THROUGH TUESDAY. A STRONGER SYSTEM WILL BRING A COLD FRONT INTO
THE COASTAL WATERS TUESDAY CLEARING OUT THE AREA. HOWEVER... THIS
FRONT IS STRONG ENOUGH TO PRODUCE SOME STRONG WINDS ASSOCIATED
WITH THE COLD AIR ADVECTION ACROSS A FRICTIONLESS WATER SURFACE.
THE WINDS AND ROUGH SEAS WILL LIKELY WARRANT A SMALL CRAFT
ADVISORY TUE AND WED. MARINERS SHOULD PLAN ACCORDINGLY FOR THE
MIDDLE OF NEXT WEEK. KEG

DECISION SUPPORT...
DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
             CITY OF NEW ORLEANS DSS SUPPORT
             MONITORING HEAVY RAINFALL POTENTIAL AND ISOLATED TSTORMS.

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  52  43  56  45 / 100  90  20  10
BTR  59  45  59  46 / 100  80  20  10
ASD  59  47  62  49 /  90  80  40  10
MSY  64  52  61  52 /  90  70  30  10
GPT  55  48  60  51 / 100  70  40  10
PQL  59  43  63  45 / 100  70  50  10

&&

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

$$





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