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

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

140
FXUS64 KLIX 160914
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
414 AM CDT THU APR 16 2015

.SHORT TERM...

LITTLE CHANGE IN THINKING FROM THE PREVIOUS FORECAST...AS THE AREA
REMAINS UNDER THE INFLUENCE OF A BROAD REGION OF ENHANCED OMEGA
THROUGH SATURDAY AS A SLOW MOVING UPPER LEVEL TROUGH OVER THE FOUR
CORNERS DRIFTS THROUGH THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY. SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS ASSOCIATED
WITH PULSES UP INCREASED VORTICITY EJECTING OUT OF THE BASE OF THE
PARENT UPPER LEVEL LOW WILL IMPACT THE REGION THROUGH THIS
PERIOD...WITH THE RISK OF HEAVY RAINFALL AND LOCALLY SEVERE
THUNDERSTORMS EACH DAY. HOWEVER... THE RISK OF SEVERE
THUNDERSTORM DEVELOPMENT WILL BE GREATEST ON FRIDAY AND SATURDAY
AS OVERALL LAPSE RATES AND SHEAR PROFILES LOOK MORE FAVORABLE ON
THESE DAYS. THERE WILL BE A THREAT OF HEAVY RAINFALL THREAT EVERY
DAY AS PW VALUES REMAIN ELEVATED AT AROUND 1.75 INCHES AND THE
ATMOSPHERE REMAINS MOISTURE LOADED. GIVEN THIS THREAT...THE FLASH
FLOOD WATCH REMAINS IN EFFECT THROUGH FRIDAY EVENING. THE WATCH
MAY NEED TO BE EXTENDED INTO SATURDAY LATER TODAY.

FOR TODAY...AFTER REVIEWING THE GFSBUFR SOUNDINGS AND LOOKING AT
THE LATEST HRRR OUTPUT...EXPECT TO SEE CONVECTION INITIALLY IMPACT
AREAS AROUND BATON ROUGE THIS MORNING AND THEN SPREAD SOUTH AND
EAST INTO NEW ORLEANS AND THE MISSISSIPPI GULF COAST DURING THE
AFTERNOON AND EVENING HOURS. SOUNDING PROFILES ARE NOT AS
SUPPORTIVE OF SEVERE THUNDERSTORMS TODAY...AS MID-LEVEL LAPSE
RATES ARE CLOSER TO MOIST ADIABATIC AND THE WET BULB ZERO HEIGHT
REMAINS AROUND 13K FEET. ADDITIONALLY...THERE IS VERY LITTLE WIND SHEAR
NOTED OVER THE AREA. SPC HAS ONLY A MARGINAL RISK OF SEVERE
THUNDERSTORM DEVELOPMENT TODAY GIVEN THESE WEAKER PARAMETERS.
THE SOUNDING IS SUPPORTIVE OF LOCALLY HEAVY RAINFALL DEVELOPING
TODAY. THERE IS LITTLE IN THE WAY OF CONVECTIVE INHIBITION...SO IT
WILL NOT TAKE MUCH TO GET THUNDERSTORMS GOING. THESE THUNDERSTORMS
WILL HAVE A VERY EFFICIENT RAIN PROCESS...WHICH WILL ALLOW FOR
RAINFALL RATES OF UP TO 2 INCHES PER HOUR AT TIMES. THUS...SOME
LOCALIZED FLOODING WILL BE THREAT TODAY.

HEADING INTO TONIGHT...MUCH AS SEEN THE LAST FEW NIGHTS...THE
THUNDERSTORM ACTIVITY WILL QUICKLY DIMINISH AS DAYTIME HEATING
GIVES WAY. THERE WILL BE A RISK OF SOME SCATTERED SHOWERS AND B
THUNDERSTORMS DEVELOPING DURING THE NIGHT...BUT OVERALL COVERAGE
WILL BE MUCH LOWER THAN DURING THE PEAK HEATING HOURS.
TEMPERATURES WILL ONCE AGAIN COOL BACK INTO THE MIDDLE TO UPPER
60S...AND SOME PATCHY FOG WILL DEVELOP TOWARD DAYBREAK DUE TO THE
WET GROUND CONDITIONS AND A WEAK LOW LEVEL INVERSION CUTTING OFF
THE BOUNDARY LAYER WINDS. FOG COVERAGE LOOKS TO BE LOW ENOUGH TO
KEEP OUT OF THE OFFICIAL FORECAST FOR NOW.

FRIDAY LOOKS TO BE A VERY ACTIVE DAY ACROSS THE REGION. GFSBUFR
SOUNDINGS SHOW A MUCH MORE FAVORABLE ENVIRONMENT FOR SEVERE
THUNDERSTORM DEVELOPMENT...ESPECIALLY FROM LATE MORNING ON. MID-
LEVEL LAPSE RATES WILL INCREASE DRAMATICALLY FRIDAY
AFTERNOON...SHOOTING UP TO 7 C/KM BETWEEN 700 AND 500 MB. THESE
HIGH LAPSE RATES WILL ALSO BE ABOVE THE FREEZING LEVEL WHICH WILL
FALL BELOW 13K FEET. ADDITIONALLY...WET BULB ZERO HEIGHTS WILL
DROP TO AROUND 11K FEET. WITH STRONG LAPSE RATES IN THE HAIL
GROWTH ZONE...SOME LARGE HAIL WILL ONCE AGAIN BE POSSIBLE ON
FRIDAY. LOOKING AT THE WIND PROFILE...OVERALL HELICITY VALUES WILL
BE FAIRLY WEAK ON FRIDAY...BUT WITH SOME DRY AIR ADVECTING INTO
THE MID-LEVELS...THE THREAT OF STRAIGHT LINE WINDS AND BOWING
SEGMENTS INCREASES. THERE IS ENOUGH LOW LEVEL HELICITY...THAT AN
ISOLATED TORNADO COULD NOT BE RULED OUT FRIDAY AFTERNOON.
OVERALL...EXPECT THE MAIN THREAT TO BE HAIL AND STRAIGHT LINE
WINDS ON FRIDAY. CONDITIONS WILL ONCE AGAIN IMPROVE DURING THE
EVENING HOURS ON FRIDAY AS THE VORT MAX SLIDES TO THE EAST AND THE
ATMOSPHERE STABILIZES A BIT.

HOWEVER...THE PARENT UPPER LEVEL TROUGH WILL BEGIN TO DIRECTLY
IMPACT THE REGION ON SATURDAY AS IT MOVES THROUGH THE SOUTHERN
PLAINS. SATURDAY LOOKS TO HAVE THE HIGHEST THREAT OF BOTH HEAVY
RAINFALL AND SEVERE THUNDERSTORMS. PW VALUES WILL BE VERY
HIGH...APPROACHING 2 INCHES...AND THE OVERALL LAPSE RATES WILL
TURN MORE MOIST ADIABATIC THROUGH THE DAY. THIS WILL DECREASE THE
HAIL THREAT SUBSTANTIALLY...WITH WET BULB ZERO HEIGHTS REMAINING
WELL ABOVE 13K FEET. HOWEVER...VERY EFFICIENT RAINFALL PROCESSES
WILL DEVELOP...RESULTING IN HOURLY RAINFALL RATE POTENTIAL OF 2 TO
3 INCHES IF A STORM STALLS OVER THE SAME AREA. FORTUNATELY...THE
STORMS WILL BE FAST MOVING...SO ACTUAL RAINFALL RATES WILL BE
LOWER. THESE STRONG WINDS WILL UNFORTUNATELY MEAN THAT THE RISK OF
STRAIGHT LINE WINDS AND TORNADOES WILL BE HIGH ON SATURDAY. 0-3KM
SHEAR WILL INCREASE TO AROUND 35 KNOTS AND STORM RELATIVE HELICITY
VALUES WILL RISE TO AROUND 250 M2/S2 SATURDAY AFTERNOON. THESE
VALUES ARE VERY CONDUCIVE TO ROTATING THUNDERSTORM
DEVELOPMENT...AND THUS THE FORMATION OF TORNADOES. A FRONTAL
BOUNDARY WILL PUSH THROUGH THE AREA SATURDAY NIGHT...WHICH WILL
KEEP THE RISK OF SHOWERS AND THUNDERSTORMS IN PLACE THROUGH THE
NIGHT...AND HAVE LIKELY POPS IN PLACE TO REFLECT THIS.

.LONG TERM...

CONDITIONS WILL BEGIN TO IMPROVE ON SUNDAY...AS A COLD FRONT
PUSHES OFFSHORE AND RAIN CHANCES SHOULD DECREASE THROUGH THE DAY
FROM WEST TO EAST. THE PARENT UPPER LEVEL TROUGH AXIS WILL FINALLY
PUSH THROUGH THE REGION SUNDAY NIGHT...WITH INCREASING NEGATIVE
VORTICITY ADVECTION AND SUBSIDENCE TAKING HOLD OF THE AREA FOR
MONDAY. AT MOST...THERE COULD BE SOME LINGERING SHOWERS AND CLOUDS
ALONG THE IMMEDIATE COAST MONDAY MORNING...WITH CLEARING
CONDITIONS EXPECTED BY MONDAY AFTERNOON. AS A MORE ZONAL FLOW
REGIME TAKES HOLD ALOFT...AND SOME DRIER MID-LEVEL AIR LINGERS
OVER THE AREA SKIES SHOULD REMAIN PARTLY CLOUDY AND RAIN CHANCES
WILL BE LESS THAN 10 PERCENT FOR TUESDAY. TEMPERATURES WILL REMAIN
NEAR NORMAL...WITH HIGHS IN THE LOWER 80S AND LOWS IN THE UPPER
50S AND LOWER 60S.

UNFORTUNATELY...A WEAK IMPULSE RIDING ALONG THE ZONAL FLOW WILL
SLIDE THROUGH THE AREA ON WEDNESDAY. THE SYSTEM WILL BE FAIRLY
WEAK...BUT ENOUGH FORCING AND MOISTURE WILL BE IN PLACE TO SPARK
OFF SOME SCATTERED SHOWERS AND THUNDERSTORMS DURING THE DAY ON
WEDNESDAY. RAIN CHANCES WILL BE HIGHEST ALONG THE COAST AND
OFFSHORE WHERE OVERALL MOISTURE AND FORCING IS EXPECTED TO BE
GREATEST. AS THIS FEATURE PULLS TO THE EAST WEDNESDAY...SKIES
SHOULD CLEAR AND RAIN CHANCES WILL DROP. HOWEVER...ANOTHER IMPULSE
WILL SLIDE THROUGH ON THURSDAY...BRINGING ANOTHER CHANCE OF
ISOLATED SHOWERS AND THUNDERSTORMS FOR THURSDAY.

&&

.AVIATION...

TAFS WILL BE DEPENDENT ONCE AGAIN ON EVENTUAL CONVECTIVE DEVELOPMENTS TODAY.
CONVECTIVE BASED MODELS SUGGEST ONSET OF STORMS COULD IMPACT SOME LOCATIONS
BY 14Z...PRIMARILY WESTERNMOST LOCATIONS LIKE KBTR AND KHUM...THOUGH ALL
TERMINALS SHOULD SEE SOME PERIODS OF TSRA/SHRA THROUGHOUT THE DAY. DOWN BURST
POTENTIAL WILL BE HIGH TODAY WITH GUST POTENTIAL 35-45 KT. EFFICIENT RAINFALL
PROCESS SHOULD ALSO LOWER VSBY TO VLIFR LEVELS AT TIMES DURING HEAVY RAINFALL.
OTHERWISE...VFR CONDITIONS SHOULD PREVAIL AFTER 16Z OUTSIDE
CONVECTION.

&&

.MARINE...

AN INTERESTING WAKE LOW PHENOMENA IMPACTED THE OFFSHORE WATERS
THIS MORNING...BUT THIS HAS SINCE WEAKENED. OVERALL...EXPECT TO
SEE AN ONSHORE FLOW OF 10 TO 15 KNOTS REMAIN OVER THE COASTAL
WATERS THROUGH FRIDAY. AS AN UPPER LEVEL LOW AND ASSOCIATED WEAK
SURFACE LOW AND FRONT MOVE THROUGH OVER THE WEEKEND...WINDS WILL
INCREASE INTO EXERCISE CAUTION RANGE SATURDAY AND REMAIN ELEVATED
INTO SUNDAY. SEAS WILL RESPOND AND INCREASE TO 3 TO 5 FEET IN THE
OFFSHORE WATERS. THE GRADIENT WILL EASE OVER THE AREA ON
MONDAY...ALLOWING FOR WEAKER AND MORE VARIABLE FLOW OF 10 KNOTS OR
LESS. SEAS WILL ALSO FALL BACK INTO THE 1 TO 3 FEET RANGE FOR
MONDAY AND TUESDAY.

&&

.DECISION SUPPORT...

DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...MONITORING HEAVY RAINFALL/FLOODING POTENTIAL
             ASSESSING SEVERE WEATHER THREAT THRU WEEKEND.

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  78  65  79  66 /  80  60  70  50
BTR  79  66  81  67 /  80  60  70  50
ASD  78  67  80  68 /  70  70  70  60
MSY  78  69  80  69 /  70  70  70  60
GPT  77  68  78  69 /  70  70  70  70
PQL  78  67  79  69 /  70  70  70  70

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...FLASH FLOOD WATCH THROUGH FRIDAY EVENING FOR LAZ040-046>050-
     056>070-072.

GM...NONE.
MS...FLASH FLOOD WATCH THROUGH FRIDAY EVENING FOR MSZ077-080>082.

GM...NONE.
&&

$$

32



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.