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

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041
FXUS64 KLIX 181641
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1141 AM CDT SAT APR 18 2015

.UPDATE...

UPDATED TO TRIM POPS BACK CONSIDERABLY FOR THE REMAINDER OF THE
DAY. CONVECTION MOVING AWAY FROM MOST LAND AREAS. CONVECTION
OFFSHORE WILL BLOCK BEST INFLOW FROM REACHING LAND FOR AT LEAST
SEVERAL MORE HOURS. WILL REASSESS FOR AFTERNOON PACKAGE...BUT 12Z
GUIDANCE INDICATING CURRENT FORECAST POPS WILL NEED REVISING. WILL
CONTINUE FLASH FLOOD WATCH...BUT THREAT SEEMS TO BE LOWERING
SOMEWHAT. 35

&&

.PREV DISCUSSION... /ISSUED 822 AM CDT SAT APR 18 2015/

..SOUNDING DISCUSSION...
THE SOUNDING THIS MORNING CAPTURED A CALM PERIOD IN THE WINDS AT
LOW LEVELS. THEREFORE THERE IS NOT REALLY A SHEAR PROFILE PRESENT
THOUGH WINDS ARE ABOUT 50 KTS AT 500 MB. THERE IS A SFC INVERSION
UP TO 1000 FT... MU CAPE IS 1200 J/KG FROM PARCEL CONDITIONS IN
THAT LAYER BUT MIXED LAYER CAPE IS 340 J/KG. BETTER INGREDIENTS
FOR A SEVERE THREAT LATER TODAY WOULD NEED TO COME FROM MORE OF A
SOUTHWEST FLOW AT LOW LEVELS AND A BIT OF DESTABILIZATION WITH
DAYTIME HEATING... HOWEVER RAIN ACROSS THE AREA THIS MORNING FOR
THE NEXT COUPLE HOURS AND OVERCAST SKIES TODAY WILL LIMIT HEATING.
THERE IS A LOT OF MOISTURE IN THE PROFILE WITH PW NEAR THE DAILY
MAX AT 1.86 INCHES.
KRAUTMANN

PREV DISCUSSION... /ISSUED 436 AM CDT SAT APR 18 2015/

SHORT TERM...

THE REMAINS OF AN MESOSCALE CONVECTIVE SYSTEM ARE CURRENTLY MOVING
THROUGH THE FORECAST AREA. THERE IS SOME THUNDERSTORM ACTIVITY
ALONG THE SOUTHERN PERIPHERY OF THIS CONVECTIVE SYSTEM WHERE
OVERALL INSTABILITY IS GREATEST. HOWEVER...THERE IS A FAIRLY
STABLE AIRMASS IN THE LOW LEVELS...SO NO SIGNIFICANT IMPACTS OTHER
THAN SOME LOCALLY HEAVY RAINFALL AND LIGHTNING ARE EXPECTED WITH
THIS FEATURE AS IT MOVES ALONG THE IMMEDIATE LOUISIANA COASTLINE
BEFORE DAYBREAK. UNFORTUNATELY...STRONG JET DYNAMICS AND ANOTHER
WAVE OF INCREASED VORTICITY ARE SWEEPING TOWARD THE REGION FROM
SOUTH TEXAS THIS MORNING. THIS SECOND WAVE SHOULD IMPACT THE AREA
BEGINNING LATER THIS MORNING AND THEN PERSIST INTO THE AFTERNOON
HOURS. HAVE WENT WITH CATEGORICAL POPS FOR THE ENTIRE AREA THROUGH
THE DAY...AND EXPECT TO SEE A FAIRLY BROAD AREA OF MODERATE RAIN
WITH EMBEDDED THUNDERSTORMS IMPACT THE REGION. OVERALL SHEAR
VALUES WILL BE FAVORABLE FOR SOME STRONG TO POSSIBLY SEVERE
CONVECTION TO DEVELOP LATER THIS MORNING INTO THE AFTERNOON HOURS.
STORM RELATIVE HELICITY VALUES WILL RANGE FROM 150 TO 200 M2/S2
AROUND MIDDAY...AND 0-3KM SHEAR VALUES WILL PEAK AT AROUND 30
KNOTS DURING THIS TIME FRAME. THE PRIMARY THREAT FROM ANY STRONGER
CONVECTION COULD BE STRAIGHT LINE WINDS AND ISOLATED TORNADOES.

HEADING INTO THE OVERNIGHT HOURS...CONVECTIVE CHANCES WILL
DECREASE THROUGH THE EVENING HOURS...AS THE STRONGEST FORCING
SHIFTS TO THE NORTH AND EAST. HOWEVER...THE REGION WILL STILL
REMAIN BELOW AN UPPER LEVEL JET STREAK AND HIGHLY DIFLUENT FLOW.
THUS...EXPECT TO SEE SCATTERED SHOWERS AND THUNDERSTORMS LINGER
THROUGH THE OVERNIGHT HOURS. THE SEVERE THREAT LOOKS MORE LIMITED
GIVEN THE LACK CAPE AND SHEAR OVER THE AREA. A FRONTAL BOUNDARY
WILL SWEEP THROUGH THE AREA TOMORROW MORNING...WITH RAIN CHANCES
ENDING FROM WEST TO EAST THROUGH THE MORNING HOURS. EXPECT TO SEE
THE VAST MAJORITY OF THE PRECIPITATION WELL OFFSHORE BY SUNDAY
EVENING AS STRONG DRY AIR ADVECTION TAKES HOLD OF MOST OF THE
FORECAST AREA.

THE PARENT UPPER LEVEL TROUGH AXIS WILL FINALLY SWEEP THROUGH
SUNDAY NIGHT AND WINDS WILL SHIFT TO THE NORTH. THERE COULD BE
SOME ISOLATED SHOWERS THAT DEVELOP IN ADVANCE OF THE TROUGH AXIS
SUNDAY NIGHT...BUT THE OVERALL THREAT OF RAIN SHOULD BE QUITE LOW.
ONCE THE TROUGH AXIS MOVES THROUGH...A SURGE OF DRIER AND COOLER
AIR WILL SWEEP INTO THE LOW LEVELS OF THE ATMOSPHERE. TEMPERATURES
ON MONDAY SHOULD BE SLIGHTLY COOLER THAN NORMAL UNDER MOSTLY SUNNY
SKIES.

LONG TERM...

A ZONAL FLOW REGIME WILL DOMINATE THE GULF SOUTH ON TUESDAY AND
WEDNESDAY. A VERY DRY AND STABLE AIRMASS WILL REMAIN IN CONTROL OF
THE AREA ON TUESDAY...WITH COOLER THAN NORMAL TEMPERATURES AND
PARTLY CLOUDY SKIES EXPECTED. HOWEVER...A WEAK AND FAST MOVING
UPPER LEVEL VORT LOBE WILL SWEEP THROUGH THE REGION ON WEDNESDAY.
A SLIGHT INCREASE IN OMEGA OVER THE AREA...AND MORE FAVORABLE
LAPSE RATES WILL ALLOW FOR SOME ISOLATED TO SCATTERED CONVECTION
TO DEVELOP DURING THE PEAK HEATING HOURS ON WEDNESDAY. WITH AN
INCREASE IN MOISTURE OVER THE AREA...TEMPERATURES WILL MODERATE
BACK INTO THE UPPER 70S AND LOWER 80S WEDNESDAY AFTERNOON. THESE
WARMER TEMPERATURES WILL SPILL INTO WEDNESDAY NIGHT WITH LOWS
CLIMBING BACK INTO THE 60S ACROSS THE AREA.

A WEAK UPPER LEVEL RIDGE WILL DEVELOP OVER THE GULF SOUTH ON
THURSDAY AND FRIDAY...AND WARMER TEMPERATURES IN THE MIDDLE 80S
ARE EXPECTED EACH DAY. OVERALL LIFT WILL BE FAIRLY LIMITED...BUT
THERE SHOULD BE JUST ENOUGH INSTABILITY TO SPARK OFF SOME WIDELY
SCATTERED AFTERNOON CONVECTION EACH DAY. HIGHS WILL EASILY CLIMB
INTO THE MIDDLE TO UPPER 80S EACH DAY...AND OVERNIGHT LOWS WILL
ONLY DIP INTO THE UPPER 60S AND LOWER 70S. OVERALL...THE LATTER
PART OF THE WEEK WILL BE VERY REMINISCENT OF SUMMER.

AVIATION...

RAIN/SHRA WITH EMBEDDED TSRA WILL IMPACT THE TAF AIRPORTS FOR MUCH
OF THE DAY...AND WILL CONTINUE TO HAVE TO REFINE THE TIMING OF THE
ASSOCIATED LOWER CONDITIONS. THE LOWER VSBYS IN FOG AND VERY LOW
CIGS AT KMCB AND KGPT SHOULD MIX OUT BEFORE 10-11Z AS THE RAIN MOVES
IN...HOWEVER AT LEAST MVFR CONDITIONS ARE EXPECTED TO PERSIST MUCH
OF TODAY WITH SOME TEMPO IFR POSSIBLE. 22/TD

MARINE...

AN AREA OF LOW PRESSURE IS EXPECTED TO GAIN STRENGTH AS IT MOVES
NORTHEAST FROM NEAR THE TEXAS/LOUISIANA BORDER EARLY TODAY ACROSS
THE LOWER MISSISSIPPI VALLEY TONIGHT. MOSTLY LIGHT TO MODERATE
SOUTHERLY WINDS ARE EXPECTED...ALTHOUGH VARIABLE WINDS WITH MUCH
STRONGER GUSTS ARE LIKELY TODAY WITH THUNDERSTORM LINES AND
CLUSTERS. A SLIGHT INCREASE IN GRADIENT FLOW TOMORROW COULD PUSH
WINDS IN EXERCISE CAUTION RANGE IN THE OFFSHORE WATERS FOR A BRIEF
PERIOD. WINDS WILL TURN OFFSHORE SUNDAY NIGHT AND MONDAY AS A
RIDGE OF HIGH PRESSURE SETTLES IN. OVERALL...FAIRLY BENIGN
CONDITIONS WILL DOMINATE EARLY NEXT WEEK...WITH WINDS VEERING TO
THE EAST AND THEN SOUTHEAST AND REMAINING AT 10 KNOTS OR LESS.
SEAS WILL GENERALLY BE IN THE 2 TO 4 FEET RANGE DURING THIS
PERIOD.

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  75  64  84  61 / 100  40  20  20
BTR  77  65  85  62 / 100  40  10  20
ASD  77  66  84  65 /  90  50  20  20
MSY  78  68  85  68 / 100  50  20  20
GPT  77  69  81  69 /  90  50  30  20
PQL  77  66  82  67 /  90  60  30  20

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...FLASH FLOOD WATCH UNTIL 7 PM CDT THIS EVENING FOR LAZ034>037-039-
     040-046>050-056>072.

GM...NONE.
MS...FLASH FLOOD WATCH UNTIL 7 PM CDT THIS EVENING FOR MSZ077-080>082.

GM...NONE.
&&

$$



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