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

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474
FXUS64 KLIX 191318
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
818 AM CDT SUN APR 19 2015

...SOUNDING DISCUSSION...
THE SOUNDING THIS MORNING IS LOOKING A BIT DIFFERENT FROM THE PAST
WEEK AS A NEW AIRMASS IS FINALLY BEGINNING TO MOVE INTO THE AREA.
MOISTURE IS STILL HIGH AT LOW LEVELS WITH 60 F DEWPOINTS UP TO 925
MB BUT BECOMING SHALLOW. MUCH DRIER AIR IS ALOFT RESULTING IN AN
OVERALL PW AT 1.32 INCHES... WHICH IS LOWER THAN WHAT HAS BEEN
OBSERVED LATELY BUT STILL ABOVE AVERAGE. THE PROFILE IS UNSTABLE
WITH 1200 J/KG MIXED LAYER CAPE AND 1850 J/KG MU CAPE. MID LEVEL
LAPSE RATES HAVE STEEPENED SIGNIFICANTLY TO 6.5 TO 7 C/KM AS THE
UPPER LOW APPROACHED OVERNIGHT. THERE IS AN INTERESTING SHEAR
PROFILE WITH THE BASE OF THE UPPER TROUGH NEARBY. WINDS ARE SW
FROM THE SFC TO 500 MB THEN BECOME SSW AND INCREASE IN SPEED TO A
110 KT JET MAX AT 220 MB. DESPITE DRYING AIR AT LOW LEVELS AND
BETTER FORCING TO THE NORTH OF THE AREA... ANY STORMS THAT CAN
FORM LATER TODAY COULD BECOME SEVERE.
KRAUTMANN

&&

.PREV DISCUSSION... /ISSUED 528 AM CDT SUN APR 19 2015/

SHORT TERM /TODAY THROUGH TUESDAY NIGHT/...

ALTHOUGH THERE WILL BE FEWER SHOWERS AND THUNDERSTORMS OVER LAND
AREAS TODAY...THE THUNDERSTORMS THAT ARE AROUND WILL HAVE TO BE
CLOSELY MONITORED FOR POTENTIAL SEVERE WEATHER...ESPECIALLY THIS
EVENING ACROSS MAINLY NORTH AND NORTHWEST PORTIONS OF THE AREA.
MORE NUMEROUS THUNDERSTORMS...MANY APPEARING STRONG TO
SEVERE...WERE OCCURRING OVER MUCH OF THE COASTAL WATERS EARLY THIS
MORNING...AND THESE ARE LIKELY TO PERSIST THROUGH MUCH OF THE
MORNING BEFORE MOVING EAST BY AROUND MIDDAY AS ASSOCIATED UPPER
SHORTWAVE TROUGH AND DIVERGENCE MAX MOVES EAST. HIGHER
PRECIPITABLE WATER VALUES OVER OVER 1.75 INCHES ARE ALSO
ASSOCIATED WITH THIS AREA OF NUMEROUS THUNDERSTORMS OFFSHORE...BUT
THE MODELS ALSO FLUSH OUT THIS MOISTURE TO THE EAST DURING THE
MORNING HOURS. PRECIPITABLE WATER VALUES ARE THEN ONLY EXPECTED TO
RANGE FROM AROUND 1 INCH TO MAYBE NEAR 1.2 INCHES IN POCKETS AS
THE COLD FRONT APPROACHES THIS EVENING. ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS ARE EXPECTED OVER LAND AREAS THIS
MORNING...THEN THIS AFTERNOON LOOKS MOSTLY DRY AS WE AWAIT THE
MAIN SHORTWAVE TROUGH AXIS AND COLD FRONTAL PASSAGE TONIGHT. WILL
STILL BE CARRYING A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS
ACROSS ALL AREAS THIS AFTERNOON SINCE INSTABILITY IS EXPECTED TO
MODERATE TO HIGH DURING PEAK HEATING...AND A FEW STRONG TO SEVERE
THUNDERSTORMS WILL BE POSSIBLE.

THE HIGHEST POTENTIAL FOR SEVERE THUNDERSTORMS IS EXPECTED TO BE
THIS EVENING TO THE NORTH OF THE I-10/12 CORRIDOR AS THERE WILL
BE LEFTOVER MODERATE TO HIGH INSTABILITY INTERACTING WITH BETTER
FORCING FROM UPPER DIVERGENCE AND LOW LEVEL CONVERGENCE WITH THE
APPROACHING COLD FRONT. THE MAIN SEVERE WEATHER THREATS WILL BE
DAMAGING WINDS AND LARGE HAIL...HOWEVER AN ISOLATED TORNADO OR TWO
CANNOT BE RULED OUT. A FEW SHOWERS AND THUNDERSTORMS COULD LINGER
OVERNIGHT BEFORE ENDING BY DAYBREAK AS THE LONG ANTICIPATED COLD
FRONT FINALLY SWEEPS THROUGH.

A MUCH NEEDED PERIOD OF DRIER WEATHER WITH NO CHANCE OF RAIN AND
SLIGHTLY COOLER /MORE SO AT NIGHT/ AND LESS HUMID CONDITIONS IS
EXPECTED MONDAY THROUGH TUESDAY NIGHT. MONDAY SHOULD SEE PLENTY OF
SUN...BUT SOME HIGH CLOUDS ARE EXPECTED MONDAY NIGHT INTO TUESDAY
RESULTING IN PARTLY CLOUDY SKIES. HIGHS ON MONDAY AND TUESDAY ARE
EXPECTED TO REACH THE UPPER 70S TO NEAR 80...HOWEVER THE LOWS ON
MONDAY AND TUESDAY NIGHTS ARE EXPECTED TO DROP INTO THE 50S TO
LOWER 60S.

LONG TERM /WEDNESDAY THROUGH SATURDAY NIGHT/...

UNFORTUNATELY...RAIN CHANCES RETURN FOR THIS ENTIRE
PERIOD...ALTHOUGH IT IS NOT EXPECTED TO BE NEARLY AS WET AS THE
LAST WEEK TO 10 DAYS. SURFACE HIGH PRESSURE WILL SHIFT EAST
WEDNESDAY WHICH WILL BRING A RETURN OF LOW LEVEL SOUTHERLY WINDS
AND GULF MOISTURE. THE FORECAST AREA WILL BE NEAR THE EASTERN SIDE
OF A SHORTWAVE RIDGE ALOFT WHILE AREAS TO OUR NORTHEAST WILL BE IN
NORTHWEST FLOW WITH DISTURBANCES MOVING THROUGH IN THE WEDNESDAY
THROUGH THURSDAY TIME FRAME. THIS WILL ALSO LIKELY PUSH A SLOW
MOVING COLD FRONT INTO THE DEEP SOUTH. LATER IN THE WEEK...THE
SHORTWAVE RIDGE ALOFT MAY MOVE RIGHT OVER TO JUST EAST OF THE
FORECAST AREA WHILE FLATTENING OUT AS DISTURBANCES START TO MOVE
OUT OF THE BAJA MEXICO REGION. THE MODELS HAVE SOME DIFFERENCES
AND DIFFICULTIES IN HANDLING THE TIMING AND POSITION OF THESE
MINOR SYSTEMS...AND IT IS HARD TO TIME THE WETTER PERIODS WITH
CONFIDENCE. RIGHT NOW...A BLEND OF THE GFS AND ECMWF INDICATE
HIGHER RAIN CHANCES ON THURSDAY AND ESPECIALLY FRIDAY BEFORE A
POSSIBLE DRYING TREND ON SATURDAY. TEMPERATURES ARE EXPECTED TO BE
WARM AND ABOVE THE SEASONAL NORMALS THROUGH THE PERIOD. 22/TD

AVIATION...

IFR CEILINGS RUNNING BETWEEN 800 AND 1000 FEET HAVE DEVELOPED IN THE
LAST HOUR.  HAVE INCLUDED A TEMPO GROUP TO REFLECT THESE CONDITIONS
THROUGH AROUND 12-13Z.  THE LOW LEVEL INVERSION WILL QUICKLY LIFT
AFTER 13Z...ALLOWING ANY CEILINGS AND POTENTIAL FOG TO BURN OFF.
ONCE THE INVERSION LIFTS...DRIER AIR ADVECTING INTO THE MID-LEVELS
OF THE ATMOSPHERE WILL QUICKLY MIX DOWN.  OVERALL...EXPECT VFR
CONDITIONS WITH A SCATTERED DECK OF CLOUDS AROUND 2000 TO 4000 FEET
THROUGH 00Z.  THERE COULD BE SOME PATCHY FOG FORMATION EARLY
TOMORROW MORNING AROUND DAYBREAK.  KMCB AND KHUM COULD SEE A BRIEF
PERIOD OF IFR VISIBILITY RESTRICTIONS IF THE FOG FORMS. 32

MARINE...

A SLIGHT INCREASE IN GRADIENT FLOW FROM THE SOUTHWEST WILL IMPACT
THE EASTERN LEGS OF THE COASTAL WATERS TODAY INTO EARLY TONIGHT.
SMALL CRAFT EXERCISE CAUTION CONDITIONS CAN BE EXPECTED DURING THIS
PERIOD OVER THE EASTERN WATERS.  WINDS WILL THEN VEER TO THE
NORTHWEST AND NORTH TOMORROW IN THE WAKE OF A PASSING COLD FRONT.
THIS OFFSHORE FLOW OF AROUND 15 KNOTS WILL CONTINUE INTO
TUESDAY...WITH SOME CONTINUED VEERING OF THE WINDS TO THE EAST BY
TUESDAY EVENING.  OVERALL...SEAS WILL GENERALLY RANGE FROM 3 TO 5
FEET DURING THIS PERIOD.  AS HIGH PRESSURE BECOMES CENTERED TO THE
EAST OF THE AREA FOR WEDNESDAY AND THURSDAY...WINDS WILL TAKE ON A
SOUTH-SOUTHEAST COMPONENT AND WEAKEN TO BETWEEN 10 AND 15 KNOTS.
SEAS WILL FALL BACK TO AROUND 2 TO 3 FEET AS THIS OCCURS.  32

DECISION SUPPORT...

DSS CODE...YELLOW.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...NONE.

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  83  62  77  53 /  30  40  10   0
BTR  85  65  79  56 /  30  30  10   0
ASD  83  67  80  56 /  30  20  10   0
MSY  84  69  80  61 /  30  20  10   0
GPT  82  70  80  58 /  30  20  10   0
PQL  82  68  81  55 /  40  20  10   0

&&

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

$$



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