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

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574
FXUS64 KLIX 282111
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
411 PM CDT SUN SEP 28 2014

.SHORT TERM...

AN ELONGATED SHORT WAVE TROUGH CURRENTLY MOVING THROUGH THE GULF
SOUTH WILL CONTINUE TO SLOWLY TRANSIT THROUGH THE REGION THROUGH
THE SHORT-TERM PERIOD. A SURFACE LOW IS CURRENTLY DEVELOPING OVER
THE LOUISIANA COAST AND SHOULD QUICKLY PULL TO THE EAST TOWARD THE
FLORIDA PANHANDLE AND GEORGIA DURING THE DAY TOMORROW. THERE IS A
FAIRLY SHARP GRADIENT BETWEEN DEEPER MOISTURE TO THE EAST OF THIS
DEVELOPING LOW AND A REGION OF LOWER MOISTURE CONTENT TO THE WEST.
THIS GRADIENT CURRENTLY LIES FROM MCCOMB TO HAMMOND TO PORT
FOURCHON. GIVEN THIS...HAVE HIGHER RAIN CHANCES GENERALLY EAST OF
THIS LINE...WITH THE HIGHEST POPS OVER PLAQUEMINES PARISH AND THE
MISSISSIPPI COAST FOR THIS EVENING. TO THE WEST OF THIS LINE HAVE
LOWERED POPS TO CHANCE COVERAGE FOR THE EVENING HOURS. AS THE LOW
SLOWLY PULLS TO THE EAST LATE TONIGHT...THE HIGHEST RAIN CHANCES
WILL GRADUALLY SHIFT OFFSHORE AND TOWARD LOWER ALABAMA AND THE
FLORIDA PANHANDLE.

THERE HAS BEEN A SIGNIFICANT CHANGE IN THE FORECAST HEADING INTO
TOMORROW AND CONTINUING THROUGH WEDNESDAY. THE LAST FEW DAYS...THE
MODELS HAVE INDICATED THAT A LINGERING TROUGH AXIS AND ASSOCIATED
LOW LEVEL FRONTAL BOUNDARY WOULD SHIFT TO THE OFFSHORE WATERS.
THIS WOULD ALLOW A DRIER AND MORE STABLE AIRMASS TO BUILD OVER THE
LAND BASED ZONES IN THE FORECAST AREA. HOWEVER...THE LAST COUPLE
OF MODEL RUNS ARE NOW INDICATING THE LOW LEVEL FRONTAL BOUNDARY
WILL SIT ALONG THE LOUISIANA AND MISSISSIPPI COASTS THROUGH MID-
WEEK. WITH THIS LOW LEVEL BOUNDARY LOCATED ALONG THE COAST...HAVE
HAD RAISED POPS INTO THE CHANCE CATEGORY FOR EACH DAY. THERE WILL
BE SOME WEAK MID TO UPPER LEVEL RIDGING PASSING THROUGH THE AREA
TOMORROW AND TUESDAY...BUT LITTLE IN THE WAY OF DRY AIR ADVECTION
IS EXPECTED NOW. EVEN WITH THE WEAK SUBSIDENCE ALOFT...ONLY A
MINIMAL CAP IS EXPECTED. DAYTIME HEATING...WEAK LOW LEVEL
CONVERGENCE...AND AMPLE LOW LEVEL INSTABILITY SHOULD BE ENOUGH TO
OVERCOME ANY WEAK CAPPING ALOFT AND SPARK OFF SCATTERED CONVECTION
EACH DAY. THE CONVECTIVE COVERAGE WILL DECREASE DURING THE
OVERNIGHT HOURS AS DAYTIME HEATING WANES.

.LONG TERM...

HEADING INTO THE LATTER HALF OF THE WEEK...THE MODELS FALL BACK
INTO GOOD AGREEMENT WITH PREVIOUS FORECASTS. A STRONG LONG WAVE
TROUGH WILL DEVELOP IN THE PLAINS STATES AND QUICKLY RACE TO THE
EAST ON THURSDAY AND FRIDAY. AS THIS TROUGH DEEPENS...A STRONG
SURFACE LOW WILL FORM OVER THE CENTRAL PLAINS AND PUSH INTO THE
GREAT LAKES STATES BY FRIDAY. AT THE SAME TIME...A STRONG COLD
FRONT WILL DEVELOP IN THE SOUTHERN PLAINS AND RACE TO THE
SOUTHEAST INTO THE LOWER MISSISSIPPI VALLEY. THE WEAK LOW LEVEL
BOUNDARY ALONG THE CENTRAL GULF COAST WILL BEGIN TO PULL BACK
NORTHWARD AS A WARM FRONT IN RESPONSE TO THIS DEEPENING BAROCLINIC
SYSTEM AND EXPECT TO SEE A VERY WARM AND HUMID AIRMASS BUILD OVER
THE AREA FOR THURSDAY. TEMPERATURES WILL BE A GOOD 5 DEGREES ABOVE
AVERAGE FOR THURSDAY...AND THE AIRMASS WILL TAKE ON A MORE SUMMER
LIKE FEEL. INCREASING POSITIVE VORTICITY ADVECTION OVER THE AREA
WILL LEAD TO GREATER FORCING AND OVERALL OMEGA IN THE MID AND
UPPER LEVELS. AT THE SAME TIME...OVERALL ATMOSPHERIC INSTABILITY
WILL ALSO BE ON THE INCREASE. AS A RESULT...EXPECT TO SEE ANOTHER
ROUND OF DIURNALLY INDUCED SCATTERED CONVECTION DEVELOP DURING THE
DAY ON THURSDAY.

THE STRONG COLD FRONT WILL RAPIDLY APPROACH THE AREA THURSDAY
NIGHT AND WILL PASS THROUGH DURING THE DAY ON FRIDAY. AS THE FRONT
MOVES THROUGH...STRONG FORCING ALONG THE BOUNDARY SHOULD ALLOW A
BAND OF SHOWERS AND THUNDERSTORMS TO FORM ALONG IT AND SWEEP
THROUGH THE FORECAST AREA. AT THIS TIME...THE SHEAR VALUES AND
OVERALL DYNAMICS WILL BE WELL NORTH OF THE FORECAST AREA. WITH
THIS IN MIND...DO NOT EXPECT TO SEE SEVERE THUNDERSTORM
DEVELOPMENT. HOWEVER...A FEW STRONGER THUNDERSTORMS CANNOT BE
RULED OUT AS THE FRONT MOVES THROUGH. THE WIND FIELD WILL BE
UNIDIRECTIONAL IN NATURE...SO THE PRIMARY THREAT WILL BE STRONG
GUSTY WINDS FROM THE DEEPEST CONVECTION.

IN THE WAKE OF THE FRONT AND A PASSING UPPER LEVEL TROUGH
AXIS...DEEP LAYER NORTHWEST FLOW WILL TAKE HOLD OF THE REGION.
STRONG NEGATIVE VORTICITY AND DRY AIR ADVECTION WILL BRING RAPIDLY
CLEARING SKIES TO THE AREA. THE AIRMASS MOVING INTO THE AREA WILL
ALSO BE COLDER...AND EXPECT TO SEE OVERNIGHT LOWS DROP INTO THE
UPPER 50S AND LOWER 60S OVER MOST OF THE FORECAST AREA FOR
SATURDAY AND SUNDAY NIGHTS. DAYTIME HIGHS WILL STRUGGLE TO REACH
INTO THE LOWER 80S OVER THE WEEKEND.

&&

.AVIATION...

MVFR CONDITIONS WILL PREVAIL THROUGH MUCH OF THE PERIOD WITH CIGS IN
THE 1500 TO 2500 FT RANGE THROUGH THIS EVENING. LOWER CIGS ARE
EXPECTED OVERNIGHT WITH SEVERAL HOURS OF IFR CONDITIONS POSSIBLE.
SHOWERS AND A FEW ISOLATED THUNDERSTORMS WILL CONTINUE TO MOVE
ACROSS THE AREA AND HAVE INCLUDED VICINITY OR PREVAILING GROUPS AT
ALL TERMINALS THROUGH ABOUT 05Z. AFTER THAT...ACTIVITY SHOULD TAPER
OFF CONSIDERABLY.

&&

.MARINE...

WINDS WILL TEND TO BE LIGHT AND VARIABLE OVER THE MARINE ZONES
THROUGH WEDNESDAY AS A WEAK LOW LEVEL BOUNDARY LINGERS OVER THE
AREA. WITH THESE LIGHTER WINDS IN PLACE...SEAS WILL GENERALLY
RANGE FROM CALM TO AROUND 2 FEET. WEDNESDAY NIGHT INTO
THURSDAY...A STRONGER PRESSURE GRADIENT BETWEEN A DEPARTING HIGH
OVER THE EASTERN SEABOARD AND A DEVELOPING LOW IN THE PLAINS WILL
ALLOW FOR MORE SUSTAINED ONSHORE FLOW OF 10 TO 15 KNOTS TO
DEVELOP. SEAS WILL INCREASE BACK TO BETWEEN 1 AND 3 FEET AS THIS
FLOW DEVELOPS AND PERSISTS INTO FRIDAY MORNING.

&&

.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  69  85  69  87 /  40  30  20  30
BTR  70  86  70  87 /  40  30  20  30
ASD  70  86  68  86 /  60  40  30  30
MSY  73  83  73  85 /  50  40  30  40
GPT  72  84  70  85 /  60  40  30  30
PQL  70  85  68  85 /  70  50  30  20

&&

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

$$

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