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

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696
FXUS64 KLIX 181734
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1134 AM CST THU DEC 18 2014

.UPDATE...
QUICK UPDATE MAINLY TO INCREASE POPS AND ADJUST WEATHER FOR THE
TODAY AND TONIGHT PERIODS TO ACCOUNT FOR HIGHER RAIN CHANCES BASED
ON RECENT RADAR TRENDS AND LATEST MODEL GUIDANCE. OTHERWISE...NO
ADDITIONAL UPDATES ARE ANTICIPATED BEFORE THE AFTERNOON PACKAGE.

&&

.PREV DISCUSSION... /ISSUED 654 AM CST THU DEC 18 2014/

..SOUNDING DISCUSSION...

THE PRECIPITABLE WATER VALUE IS INCREASING AS MOISTURE IS BEING
DRAWN INTO OUR AREA THIS MORNING. WINDS THROUGHOUT THE ATMOSPHERE
ARE FROM THE WEST OR WEST-SOUTHWEST EXCEPT IN THE LOWEST 2000
FEET. AT 37500 FEET THE MAXIMUM WIND SPEED OF 116 KNOTS WAS FOUND.
THIS MORNING/S SURFACE INVERSION IS AROUND 3300 FEET THICK. TWO
SMALLER INVERSIONS EXIST AROUND 10000 AND 25000 FEET. TEMPERATURES
ARE GENERALLY LOWER FROM 5000 FEET UP AND HIGHER BELOW 5000 FEET
COMPARED TO 24 HOURS AGO.

12Z BALLOON INFO: THE BALLOON REACHED A HEIGHT OF 20.3 MILES ABOVE
THE GROUND BURSTING 88 MILES DOWNRANGE NORTH OF GRAND BAY MS.
FLIGHT TIME THIS MORNING WAS 97 MINUTES.

ANSORGE

PREV DISCUSSION... /ISSUED 356 AM CST THU DEC 18 2014/

SHORT TERM...
HIGH PRESSURE WILL GIVE WAY TO A MORE UNSETTLED PATTERN. EACH
MODEL SOUNDING SHOWING MOISTURE RECOVERY AS PW VALUES RISE IN
RESPONSE TO A MORE EASTERLY FLOW REGIME. ROUND ONE WILL BE IN
THE FORM OF A SHORT-WAVE LATER TODAY AND TONIGHT WITH A CHANCE
OF RAIN HIGHER AS YOU GO NORTHWEST IN OUR FORECAST AREA. THE
MAIN TROUGH WILL BE ROUND TWO AS IT DIGS OVER THE CENTRAL PLAINS.
SURFACE BASED CYCLOGENISIS EVIDENT AS ALL THE MODELS AGREE ON
THE FORMATION OF A LOW PRESSURE CENTER BETWEEN KBRO AND KCRP OVER
THE KING RANCH. THE LOW IS PROGGED TO MOVE NE ACROSS THE NORTHERN
GULF OF MEXICO TO THE LOUISIANA COAST AND ACROSS SE LA/S MS ON
FRIDAY. EACH MODEL RUN IS A TAD FURTHER SOUTH WHICH ALTERS THE
IMPACT TO OUR FORECAST EACH RUN. THE LOW WILL BRING SHOWERS AND
THUNDERSTORMS TO THE AREA FRIDAY AND FRIDAY NIGHT. A WARM FRONT
WILL MOVE FROM THE GULF NORTHWARD ACROSS THE AREA FRI MORNING IN
RESPONSE TO THE APPROACHING LOW PRESSURE. WIND PROGS INDICATE A
50KT JET IN THE LOW LEVELS QUICKLY PUSHING MOISTURE NORTHWARD.
SOME SHOWERS WILL LINGER INTO SATURDAY MORNING ENDING FROM THE
WEST BY NOON. EXAMINING THE IMPACTS TO THE AREA... THE FURTHER
THE LOW TRACKS SOUTH THE LOWER THE CHANCE FOR SEVERE WEATHER FOR
SELA...SMS...AND THE MS GULF COAST. GFS QPF PROGS OVER 2 INCHES
IN AN ELONGATED BLOB FROM KLFT TO KMOB NORTH OF THE LOW. SO SEVERE
OR NOT...SOME AREAS WILL GET MUCH NEEDED RAIN...THUS FORECAST
FAIRLY HIGH POPS FROM THIS SYSTEM. LOOKING AT SOME SCIENCE FOR
SEVERE CHANCES...HIGHEST CAPE PROGGED TO PASS ALONG THE COASTAL
WATERS PEAKING AROUND 800 J/KG. NOTICED THE BEST OMEGA LIFT WELL
NORTH OF THE FRONT ALL NORTH OF LAKE PONTCHARTRAIN WHERE THE BEST
POPS AND PRECIPITATION EFFICIENCY WILL TAKE PLACE. NOT IMPRESSIVE
LAPSE RATES TO SUPPORT HAIL THREAT...HOWEVER THERE IS SOME DECENT
SHEAR. SHEAR VALUES PROGGED TO BE FROM 400 TO 580 M2/S2 IN THE 0 TO
3 KM RANGE PEAKING AT 00Z SAT. DEDUCING THE SEVERE CHANCE TAKING
INTO ACCOUNT THE CURRENT FORECAST FOR THE LOW TRACK POINTS TO A
TYPICAL LOW INSTABILITY...HIGH SHEAR... ELEVATED CONVECTIVE
THREAT. THE BEST THREAT FOR SEVERE WEATHER WOULD BE ALONG THE
COAST TO OFFSHORE HOWEVER... THERE WOULD REMAIN A THREAT FOR HEAVY
RAIN...STRAIGHT LINE WINDS... AND WITH THE HIGH SHEAR VALUES...AN
ISOLATED TORNADO OR TWO ON FRIDAY AND FRIDAY NIGHT BEFORE THE
SYSTEM MOVES EAST. KEG

LONG TERM...
ROUND THREE COMES TUESDAY WITH A SIGNIFICANT PATTERN CHANGE OVER
THE EASTERN CONUS. A LARGE ECONUS TROUGH DEVELOPS MONDAY WITH
CYCLOGENISIS OVER MT RUSHMORE PER THE GFS AND OVER THE HAWKEYE
STATE PER THE ECMWF. THE LOW CARVES AND BECOMES QUASI STATIONARY
OVER THE GREAT LAKES. THE DRAGGING BAROCLINIC ZONE WILL IMPACT OUR
AREA WITH A CHANCE FOR RAIN TUE ENDING IN THE EVENING. LOOKS LIKE
THERE WILL BE SOME SUPPORT FROM A 150KT H3 JET AND SOME
INSTABILITY. LOOKING AT 18Z TUE CONVECTIVE DATA SHOWS THE MAIN
INSTABILITY REMAINS OFFSHORE ONCE AGAIN BUT SOME STRONGER LIFT
WILL TAKE PLACE ALONG THE ENSUING BAROCLINIC ZONE. S MS CAPE
VALUES PROGGED AT 200 J/KG WITH 1200 J/KG IN OUR OFFSHORE WATERS.
THE BEST LIFT IS PROGGED IN CNTRL MS. SO...ANOTHER CHANCE FOR RAIN
AND POSSIBLY SOME THUNDERSTORMS. SEVERE LOOKS MARGINAL ONCE
AGAIN.... HOWEVER CONFIDENCE ON THIS SYSTEM IS LOW CONCERNING THE
AREAL IMPACTS. ONE THING FOR CERTAIN IS A SHARP DROP IN
TEMPERATURES FOLLOWING THE FRONT WITH A HIGH PRESSURE CENTER OVER
KHUM PEAKING AT 1019 MB. LOOKS TO BE A VERY PLEASANT DECEMBER 25TH
WITH CLEAR SKIES...HIGHS AROUND 60 AND LOWS IN THE MID 30S TO LOW
40S. WE WILL KEEP A VERY CLOSE EYE ON WHAT LOOKS TO BE A STRONG
PRESSURE GRADIENT WITH THE COLD AIR ADVECTION OR CAA WEDNESDAY.
SWAN/WWA AND SYNOPTIC MODELS INDICATED A SIGNIFICANT RISE IN SEAS
WITH THE INCREASE IN WINDS. POSSIBLE GALES IN THE COASTAL AND
OFFSHORE WATERS AND WITH AROUND 30MPH OVER LAND. KEG

AVIATION...
WARM FRONTOGENESIS PROCESS NEXT 12-18 HOURS ALONG THE GULF COAST
WILL BRING A SLOW LOWERING OF CEILINGS FROM SOUTHWEST TO NORTHEAST.
VFR CONDITIONS THROUGH AT LEAST 20Z BEFORE LOWERING TO MVFR
BKN020-025 AT KBTR AND KMCB BEFORE 19/00Z...THEN SPREADING EASTWARD
TO OTHER TERMINAL LOCATIONS BY END OF TAF VALID PERIOD. SOME IFR
CIGS AROUND BKN-OVC007 MAY DEVELOP AT KBTR BY 19/12Z. WILL HANDLE
CONVECTIVE DEVELOPMENT WITH PROB30 GROUP AT THIS TIME FOR KMCB AND
KBTR FOR AFTER 19/06Z WITH -SHRA THOUGH ISOLATED TSRA CAN NOT BE
RULED OUT BY END OF TAF PERIOD. THIS MAY BE BETTER HANDLED WITH
TEMPO GROUP IN SUBSEQUENT TAF PACKAGE ISSUANCE. 24/RR

MARINE...
AS A LOW PRESSURE SYSTEM FORMS ALONG THE TEXAS COAST AND MOVES
OVER THE COASTAL WATERS FRIDAY...WINDS WILL BECOME MORE SOUTHEAST
AND INCREASE TO 15 TO 20 KNOTS WITH SEAS 3 TO 6 FEET. WE WILL
LIKELY RAISE THE SMALL CRAFT EXERCISE CAUTION WITH THIS LOW. THERE
COULD BE SOME THUNDERSTORMS FRIDAY AND FRIDAY NIGHT... SOME STRONG
ONES AS THE LOW PASSES. HIGH PRESSURE WILL BUILD OVER THE WEEKEND
BEFORE THE NEXT SYSTEM IMPACTS THE MARINE AREA. ANOTHER LOW AND A
FRONT WILL INCREASE THE WINDS AND SEAS AGAIN MONDAY NIGHT INTO
TUESDAY. THIS SYSTEM WILL PRODUCE A STRONG PRESSURE GRADIENT AND
COULD WARRANT A SMALL CRAFT ADVISORY. THERE IS AN INDICATION IN
THE OFFSHORE WATERS ESPECIALLY IN THE EASTERN MARINE ZONES GALES
COULD BE REACHED. SEAS WILL BE 6 TO 10 FEET LATE TUESDAY AND
ESPECIALLY WEDNESDAY CREATING A VERY HAZARDOUS ENVIRONMENT FOR
MARINERS. KEG

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  60  47  53  44 /  30  40  90  60
BTR  66  50  60  46 /  30  50  80  50
ASD  67  48  61  48 /  20  40  80  70
MSY  68  55  64  53 /  20  40  80  60
GPT  63  47  58  50 /  10  30  70  70
PQL  66  42  60  45 /  10  30  70  70

&&

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

$$







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