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

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862
FXUS64 KLIX 111840
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
140 PM CDT FRI APR 11 2014

.AVIATION...
CU FIELD BETWEEN 3K AND 5K FEET HAS BECOME WELL ESTABLISHED ACROSS
THE AREA. EXPECT THIS DECK TO DISSIPATE AROUND SUNSET WITH ONLY
HIGH CIRRUS TO PREVAIL THE REST OF THE NIGHT. WINDS WILL DECOUPLE
AND FALL TO NEAR CALM AT MOST TERMINALS. LIGHT FOG IS EXPECTED
NEAR SUNRISE WITH VIS AROUND IFR/MVFR. SOUTH WINDS WILL BE
STRONGER TMR AT 10+ KNOTS.

MEFFER
&&


.PREV DISCUSSION... /ISSUED 435 AM CDT FRI APR 11 2014/

SHORT TERM...

TODAY THROUGH SATURDAY NIGHT...

SURFACE HIGH PRESSURE WILL MAINTAIN DRY CONDITIONS...HOWEVER WITH
THE CENTER HAVING SHIFTED EAST SOUTHERLY WINDS WILL BRING HIGHER
HUMIDITY BACK ALONG WITH A CONTINUED SLOW WARMING TREND TODAY
THROUGH THE WEEKEND. SOME LOWER CLOUDS WERE ALSO OBSERVED ON
SATELLITE IMAGERY AND OBSERVATIONS WITH THE INCREASING MOISTURE.
WEAK MAINLY ZONAL FLOW IS EXPECTED IN THE MID LEVELS
HOWEVER...STRONGER WINDS AT JET STREAM LEVEL ALONG WITH AN UPPER
LEVEL SHORTWAVE WILL BRING SOME HIGH CLOUDS ACROSS THE AREA TODAY.
THE MODELS CONTINUE TO SHOW A SATURATED LOW LEVEL INVERSION
DEVELOPING TONIGHT DUE TO A COMBINATION OF RADIATIONAL COOLING AND
MOISTURE ADVECTION FROM GENERALLY LIGHT SOUTHEAST WINDS. THIS SHOULD
CAUSE A BROKEN DECK OF STRATUS AND LIKELY SOME PATCHY FOG TO DEVELOP
AFTER MIDNIGHT THROUGH EARLY SATURDAY MORNING.

CONDITIONS WILL BECOME UNSETTLED IN THE WESTERN STATES SATURDAY AS
ENERGY IN THE NORTHERN AND SOUTHERN STREAMS SET THE STAGE FOR OUR
NEXT STORM SYSTEM. THE GFS AND ECMWF INDICATE SOME LIGHT QPF
OCCURRING OVER THE FORECAST AREA SATURDAY MAINLY DUE TO CONVERGENCE
BANDS IN THE SHALLOW MARINE LAYER BELOW A MID LEVEL CAPPING
INVERSION. MOISTURE LAYERS APPEAR TOO SHALLOW FOR ANY MENTION OF
MEASURABLE RAIN. THE MAV MOS GUIDANCE HAD A BIT OF A WARM BIAS
YESTERDAY SO HAVE TRIMMED BACK A DEGREE OR SO AT SOME LOCATIONS FOR
HIGHS TODAY AND SATURDAY...ESPECIALLY NEAR THE COAST WHERE
RELATIVELY COOL WATER TEMPERATURES PERSIST. 22/TD

LONG TERM...

SUNDAY THROUGH THURSDAY...

THE GFS HAS FINALLY TRENDED TOWARD THE RECENTLY MORE CONSISTENT
EUROPEAN MODEL...WHICH HAS THE BEEN THE MODEL OF CHOICE FOR THE
LAST FEW DAYS. WITH INCREASED OVERALL CONFIDENCE IN TWO DISTINCT
PERIODS OF HIGHER RAIN CHANCES IMPACTING THE REGION SUNDAY NIGHT
INTO EARLY MONDAY AND THEN IMMEDIATELY FOLLOWING ON MONDAY
NIGHT...HAVE DECIDED TO RAISE POPS FOR THIS PERIOD INTO THE LIKELY
RANGE. HEADING FURTHER INTO NEXT WEEK...THERE ARE VERY SIGNIFICANT
MODEL DIFFERENCES THAT ARISE. THE GFS SHOWS DEVELOPS A H5 5470
METER CLOSED UPPER LEVEL LOW OVER THE INTER-MOUNTAIN WEST. AT THE
SAME TIME...THE EURO SHOWS A WEAK UPPER LEVEL RIDGE AXIS FORMING
OVER THE SAME AREA. THESE LARGE DIFFERENCES TRANSLATE INTO
RADICALLY DIFFERENT SENSIBLE WEATHER IMPACTS FOR THE FORECAST AREA
LATE IN THE WEEK. THE EURO HAS BEEN MUCH MORE CONSISTENT IN THIS
PERIOD...AND CONTINUES TO SHOW A WEAK SHORT WAVE TROUGH SLIDING
THROUGH A ZONAL FLOW REGIME OVER THE GULF SOUTH ON THURSDAY. AS A
RESULT...HAVE MADE LITTLE CHANGE TO THE ONGOING FORECAST AND KEEP
SLIGHT CHANCE POPS IN PLACE FOR THURSDAY. OVERALL..THE EXTENDED
FORECAST IS MUCH MORE HEAVILY WEIGHTED TO THE EUROPEAN MODEL.

SUNDAY WILL SEE INCREASING CLOUD COVER THROUGH THE DAY...AND
STRONGER SOUTHEAST FLOW DEVELOPING IN ADVANCE OF A DEEPENING LOW
PRESSURE SYSTEM IN THE SOUTHERN PLAINS. THERE WILL BE AMPLE
FORCING DEVELOPING ALOFT IN ADVANCE OF THE APPROACHING UPPER LEVEL
LOW...BUT A LAYER OF DRY AIR FROM 850MB UP TO 500MB WILL INDUCE
ENOUGH CONVECTIVE INHIBITION TO PROHIBIT MUCH IN THE WAY OF
CONVECTIVE DEVELOPMENT ON SUNDAY. THERE MAY BE A VERY ISOLATED
MARINE LAYER SHOWER DEVELOPING BENEATH THE CAP...BUT EVEN THAT
THREAT IS VERY LOW.

SUNDAY NIGHT INTO EARLY MONDAY...SOUTHERN STREAM ENERGY WILL EJECT
OUT OF TEXAS AND BEGIN TO TAKE ON A NEGATIVE TILT AS IT MOVES INTO
THE OHIO VALLEY. AS THIS SYSTEM LIFTS OUT...A STRONG SURFACE WILL
FORM OVER NORTHERN TEXAS AND QUICKLY RACE TO THE NORTHEAST. THIS
WILL DRIVE AN UPPER LEVEL TROUGH AND WEAK SURFACE BASED BOUNDARY
THROUGH THE REGION. DIVERGENCE ALOFT COMBINED WITH SUPPORTIVE JET
DYNAMICS WILL ALLOW FOR A BAND OF CONVECTION TO FORM ALONG THIS
TROUGH AXIS AND LOW LEVEL BOUNDARY. AFTER REVIEWING MODEL
SOUNDINGS...THE THREAT FOR SEVERE THUNDERSTORM DEVELOPMENT STILL
REMAINS ELEVATED FROM LATE SUNDAY NIGHT INTO MONDAY MORNING. 0-6KM
SHEAR VALUES WILL RANGE FROM 30 TO 40 KNOTS AND HELICITY VALUES
WILL GENERALLY RANGE AROUND 250 M2/S2. LAPSE RATES WILL BE
SOMEWHAT MARGINAL...BUT CAPE VALUES OF 1000-1500 J/KG WILL BE
SUFFICIENT TO SUPPORT SOME DEEPER UPDRAFTS. GIVEN THE PARAMETERS
CURRENTLY EXPECTED...ISOLATED TORNADO AND DAMAGING WIND EVENTS
WILL BE POSSIBLE. PW VALUES WILL ALSO BE HIGH...SO SOME LOCALLY
HEAVY RAINFALL WILL ALSO BE POSSIBLE.

THE INITIAL ROUND OF CONVECTION WILL QUICKLY PULL TO THE EAST OF
THE AREA BY MONDAY AFTERNOON...BUT THE NEXT SYSTEM WILL ALREADY
BEGIN TO IMPACT THE REGION BY THIS TIME. EXPECT TO SEE ANOTHER
SURFACE LOW DEVELOP OVER THE WESTERN GULF OF MEXICO IN A REGION OF
ENHANCED BAROCLINICITY AND UPPER LEVEL OMEGA. THIS LOW WILL SWEEP
ACROSS THE FORECAST AREA MONDAY AFTERNOON AND EVENING...BRINGING
ANOTHER ROUND OF CONVECTION TO THE AREA. IN THE WAKE OF THIS
LOW...A VERY STRONG COLD FRONT WILL FINALLY SWEEP THROUGH THE
REGION. HOWEVER...SHOWER AND THUNDERSTORM ACTIVITY SHOULD LINGER
INTO TUESDAY AS THE BASE OF THE UPPER LEVEL TROUGH MOVES THROUGH
THE AREA. A FAIRLY COLD AIRMASS ALOFT WILL DROP H5 TEMPS TO
BETWEEN -10 AND -15C. THIS WILL INCREASE LAPSE RATES ALOFT AND
PRODUCE SOME ELEVATED CAPE. FORTUNATELY...THE COLD POOL WILL NOT
BE AS IMPRESSIVE AS THE LAST EVENT THIS PAST TUESDAY...SO THE
OVERALL THREAT FOR LARGE HAIL WILL BE DIMINISHED A BIT. SOME VERY
SMALL HAIL MAY DEVELOP WITH THE STRONGEST CONVECTION.

THE COLD POOL ASSOCIATED WITH THIS TROUGH WILL LINGER OVER THE
AREA THROUGH WEDNESDAY...WITH TEMPERATURES RANGING A GOOD 10 TO 15
DEGREES BELOW NORMAL FOR BOTH TUESDAY AND WEDNESDAY. SOME
MODERATION IN TEMPERATURES IS EXPECTED FOR THURSDAY AS A MORE
ZONAL FLOW PATTERN ALOFT DEVELOPS...AND WINDS TURN MORE EASTERLY.
HOWEVER...OVERALL READINGS WILL REMAIN BELOW NORMAL WITH HIGHS
ONLY RISING INTO THE LOWER TO MIDDLE 70S. A WEAK SHORTWAVE TROUGH
WILL ALSO SLIP THROUGH THE AREA ON THURSDAY. THIS FEATURE COULD
SPARK OFF ANOTHER ROUND OF ISOLATED CONVECTION. THE CONVECTION
WILL BE MOST PRONOUNCED DURING THE AFTERNOON WHEN OVERALL
INSTABILITY IS MAXIMIZED.  32

AVIATION...

LOW LEVEL MOISTURE RETURN WILL PRODUCE SOME SCATTERED TO LOCALLY
BROKEN CLOUDS WITH BASES 028-040 THIS MORNING. FOG SHOULD NOT BE AN
ISSUE THIS MORNING AS MOST VSBYS SHOULD REMAIN VERY GOOD. THE LOWEST
CLOUD LAYERS SHOULD LIFT AND MIX OUT WITH DAYTIME HEATING...SO ANY
MVFR CATEGORY CIGS SHOULD BE TEMPORARY AND BRIEF. MOSTLY VFR
CONDITIONS WILL PREVAIL THROUGH THIS EVENING. THERE IS A BETTER
CHANCE FOR BOTH STRATUS AND FOG LATE TONIGHT INTO EARLY SATURDAY
MORNING ACROSS MOST OF THE TAF AIRPORTS. CIGS MAY INITIALLY DEVELOP
AT 015-025...BUT THEY ARE LIKELY TO BUILD DOWN TO 003-007 AFTER
08-10Z WITH VSBYS LIKELY DROPPING TO 1/2 TO 2 MILES INLAND FROM THE
COAST AND IMMEDIATE SHORELINE OF THE TIDAL LAKES. 22/TD

MARINE...

INCREASING GRADIENT FLOW FROM THE SOUTHEAST WILL KEEP WINDS IN THE
10 TO 15 KNOT RANGE THROUGH SATURDAY. AS THE GRADIENT INCREASES
FURTHER IN RESPONSE TO A DEEPENING LOW PRESSURE SYSTEM IN THE
PLAINS SOUTHEAST FLOW WILL INCREASE TO BETWEEN 15 AND 20
KNOTS...RESULTING IN EXERCISE CAUTION CONDITIONS. SEAS WILL ALSO
INCREASE TO AROUND 4 TO 6 FEET IN THE OFFSHORE WATERS. THESE WINDS
WILL GRADUALLY VEER TO THE SOUTHWEST ON MONDAY...AND FINALLY SHIFT
TO THE NORTHWEST MONDAY NIGHT AS A STRONG COLD FRONT MOVES THROUGH
THE AREA. IN THE WAKE OF THIS FRONT...EXPECT TO SMALL CRAFT
ADVISORY CONDITIONS DEVELOP LATE MONDAY NIGHT AND PERSIST INTO
WEDNESDAY. SEAS WILL QUICKLY RAMP UP TO BETWEEN 6 AND 9 FEET IN
THE GULF WATERS AND 3 TO 5 FEET IN THE SOUNDS AND LAKES.  32

DECISION SUPPORT...

DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
             MONITORING RIVER FLOODING.

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  57  79  62  81 /  10  10  10  30
BTR  60  81  63  82 /  10  10  10  30
ASD  58  78  63  80 /  10  10  10  20
MSY  62  79  65  80 /  10  10  10  20
GPT  61  75  63  77 /  10  10  10  20
PQL  57  77  60  78 /  10  10  10  20

&&

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

$$







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