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

Home | Current Version | Previous Version | Graphics & Text | 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 32 33 34 35 36 37

333
FXUS64 KLIX 201323
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
723 AM CST SAT DEC 20 2014

...SOUNDING DISCUSSION...

A SATURATED PROFILE WAS SAMPLED THROUGH 10000 FEET THIS MORNING AS
SHOWERS WERE/ARE MOVING EAST OF THE CENTRAL GULF COAST. THE LOWER
LEVEL SATURATION LED TO A PRECIPITABLE WATER VALUE 1.06 INCHES.
TEMPERATURES ARE LOWER /COLDER/ BELOW 13000 FEET AND HIGHER
/WARMER/ ABOVE THAT LEVEL COMPARED TO 24 HOURS AGO. WINDS WERE
FROM THE NORTHEAST FROM THE SURFACE TO 2500 FEET AND THEN SHIFTED
TO THE NORTH AND FINALLY THE WEST BY 6000 FEET. A PEAK WIND SPEED
OF 91 KNOTS WAS LOCATED AT 37550 FEET.

12Z BALLOON INFO: NO ISSUES WITH THE FLIGHT THIS MORNING. THE
BALLOON TERMINATED AT A HEIGHT OF 20.9 MILES ABOVE THE GROUND
NORTH OF GRAND BAY MS 90 MILES DOWNRANGE FROM THE OFFICE. FLIGHT
TIME WAS 100 MINUTES.

ANSORGE

&&

.PREV DISCUSSION... /ISSUED 406 AM CST SAT DEC 20 2014/

SHORT TERM...

A SHORT WAVE TROUGH AXIS CURRENTLY EXTENDING OVER THE EASTERN
THIRD OF THE FORECAST AREA CONTINUES TO PRODUCE SOME LIGHT
RAINFALL MAINLY ALONG AND EAST OF INTERSTATE 59. AS THE SHORTWAVE
CONTINUES TO TRUCK EASTWARD THIS MORNING...RAIN CHANCES WILL
DIMINISH FROM WEST TO EAST. UNFORTUNATELY...A LOW STRATUS DECK
WILL LINGER THROUGH THE DAY AS A COOLER AND MORE STABLE AIRMASS IN
THE LOW LEVELS KEEPS A FAIRLY STRONG ELEVATED IN PLACE AROUND
950MB. WITH THIS CLOUD DECK IN PLACE MUCH OF THE DAY...TEMPERATURE
WILL STRUGGLE TO REACH INTO THE UPPER 50S THIS AFTERNOON.

ANOTHER SHORTWAVE TROUGH WILL SLIDE THROUGH THE FORECAST AREA
TONIGHT AND TOMORROW. THIS FEATURE WILL KEEP CLOUDS OVER THE AREA
THROUGH TOMORROW NIGHT...AND ALSO BRING ANOTHER ROUND OF RAINFALL
TO COASTAL WATERS AND COASTAL AREAS OF SOUTHEAST LOUISIANA AND
MISSISSIPPI...INCLUDING METRO NEW ORLEANS...BEGINNING LATE TONIGHT
AND PERSISTING THROUGH THE DAY TOMORROW. FARTHER INLAND...CLOUDS
WILL REMAIN OVER THE AREA...BUT DRIER AIR IN THE MID-LEVELS WILL
PROHIBIT THE RAINFALL OFFSHORE FROM DEVELOPING. TEMPERATURES WILL
WARM A BIT TOMORROW...WITH READINGS CLOSER TO SEASONAL NORMS FOR
LATE DECEMBER.

A PATTERN TRANSITION WILL BEGIN TO TAKE PLACE ON MONDAY...AS A
STRONG NORTHERN STREAM SHORT WAVE RIDES OVER A STRENGTHENING RIDE
ON THE WEST COAST AND BEGINS TO DESCEND DOWN THE SPINE OF THE
ROCKIES. ACROSS THE GULF SOUTH...DEEP LAYER SOUTHWEST FLOW WILL
TAKE HOLD...AND THE REGION WILL BE BENEATH THE RIGHT ENTRANCE
REGION OF A 100 KNOT JET STREAK ALOFT WHICH WILL BRING INCREASED
OMEGA ALOFT TO THE REGION. THIS SOUTHWEST FLOW REGIME WILL ALSO BRING
A WARMER AND MORE MOIST AIRMASS INTO THE REGION...WITH DEWPOINTS
CLIMBING BACK INTO THE 50S AND DAYTIME HIGHS RISING INTO THE UPPER
60S AND LOWER 70S MONDAY AFTERNOON. HOWEVER...DRY AIR IN THE MID-
LEVELS WILL LINGER THROUGH THE AFTERNOON HOURS. THIS DRIER AND
WARMER AIRMASS ALOFT WILL EFFECTIVELY CAP OFF ANY CONVECTIVE
CHANCES THROUGH THE DAY EVEN AS OMEGA VALUES INCREASE THROUGH THE
DAY.

THE CAP WILL BEGIN TO ERODE MONDAY NIGHT AS MID-LEVEL MOISTURE
FINALLY BEGINS TO INCREASE...AND EXPECT TO SEE SCATTERED SHOWERS
AND THUNDERSTORMS BEGIN TO FORM BY MIDNIGHT. SYNOPTICALLY...THE
NORTHERN STREAM ENERGY WILL BEGIN TO RAPIDLY DEEPEN OVER THE
PLAINS STATES...AS A STRONG 150 KNOT JET DESCENDS DOWN THE SPINE
OF THE ROCKIES. DURING THE OVERNIGHT HOURS...A SLIGHTLY MORE
STABLE LAYER IN THE LOW LEVELS SHOULD PROHIBIT ANY SURFACE BASED
CONVECTION. HOWEVER...LAPSE RATES ABOVE THIS STABLE LAYER WILL BE
CONDUCIVE TO SOME DEEPER THUNDERSTORMS FORMING. THESE LAPSE RATES
WILL BE FAVORABLE FOR SOME HAIL FORMATION IN THE STRONGEST STORMS.

BY TUESDAY MORNING...CONDITIONS WILL TURN MORE FAVORABLE FOR SOME
SURFACE BASED CONVECTION TO DEVELOP. ALOFT...THE REGION WILL BE
PLACED UNDER THE RIGHT ENTRANCE REGION OF A 110 KNOT JET STREAK. A
LOW LEVEL JET IN EXCESS OF 40 KNOTS WILL PRODUCE 0-3KM SPEED
SHEAR VALUES OF AROUND 30 KNOTS...AND DIRECTIONAL SHEAR WILL ALSO
BE QUITE HIGH WITH HELICITY VALUES GENERALLY RUNNING AROUND
300M2/S2. THE LARGEST LIMITING FACTOR DURING THIS PERIOD WILL BE
THE DEGREE OF INSTABILITY THAT DEVELOPS DURING THE DAY ON TUESDAY.
IF CLOUDS LINGER THROUGH THE DAY...OVERALL INSTABILITY WILL BE
REDUCED AND THE SEVERE POTENTIAL WILL BE LOWER. AT THIS
TIME...EXPECT ENOUGH INSTABILITY WITH CAPE VALUES BETWEEN 500 AND
1000 J/KG TO BE IN PLACE TO SPARK OFF CONVECTION. GIVEN THE
STRENGTH OF THE COLD FRONT AND ASSOCIATED TROUGH AXIS MOVING
IN...A LINE OF STRONG TO POSSIBLY SEVERE THUNDERSTORMS COULD PASS
THROUGH THE REGION FROM LATE TUESDAY MORNING THROUGH THE AFTERNOON
HOURS. AT THIS TIME...ALL CONVECTIVE MODES WILL BE POSSIBLE IF
SEVERE CONVECTION IS ABLE TO FORM.

LONG TERM...

RAIN CHANCES WILL QUICKLY DIMINISH BEHIND THE FRONT...AND EXPECT
TO SEE DRY CONDITIONS AND CLEARING SKIES TAKE HOLD DURING THE DAY
ON WEDNESDAY AS STRONG SUBSIDENCE AND DRY AIR ADVECTION TAKE HOLD
OF THE GULF SOUTH. A VERY COLD AIRMASS WILL ALSO ADVECT INTO THE AREA
THROUGH THE DAY WITH 1000-500MB THICKNESSES DROPPING TO AROUND
5340 METERS BY WEDNESDAY AFTERNOON. 925MB TEMPERATURES WILL PLUNGE
TO AROUND -4 DEGREES CELSIUS WHICH TRANSLATES TO HIGHS IN THE
LOWER 50S WEDNESDAY AFTERNOON. THE COLDER AIR MOVING COMBINED WITH
A STRONG PRESSURE GRADIENT OVER THE AREA WILL BRING WINDY
CONDITIONS TO THE AREA THROUGH THE DAY ON WEDNESDAY. THESE WINDS
COMBINED WITH THE COLDER TEMPERATURES WILL MAKE FOR A VERY COLD
CHRISTMAS EVE. FORTUNATELY...THE MAIN HEART OF THE COLD POOL WILL
QUICKLY PULL TO THE EAST OF THE AREA BY THURSDAY. AS A
RESULT...TEMPERATURES WILL FALL INTO THE 30S AND LOWER 40S
WEDNESDAY NIGHT...BUT SHOULD QUICKLY REBOUND BACK TO MORE NORMAL
READINGS BY THURSDAY AFTERNOON IN THE LOWER 60S. DEEP LAYER
NORTHWEST FLOW IN THE MID AND UPPER LEVELS ALONG WITH STRONG
RIDGING AT THE SURFACE SHOULD ALLOW FOR A SUNNY AND DRY CHRISTMAS
DAY.

THE RIDGE AXIS WILL SHIFT TOWARD THE EASTERN SEABOARD FOR FRIDAY
AND SATURDAY...WITH SOUTHWEST FLOW ONCE AGAIN DEVELOPING OVER THE
AREA. A WEAK SHORTWAVE TROUGH AXIS WILL ALSO SLIDE THROUGH THE
AREA DURING THIS TIME FRAME. MOISTURE IN THE MID-LEVELS AND ALOFT
WILL BE FAIRLY LIMITED...BUT LOW LEVEL MOISTURE WILL BE SWEEPING
INTO THE AREA ON THE BACK OF THE ONSHORE FLOW. EXPECT TO SEE
CLOUDS INCREASE FOR FRIDAY AND SATURDAY...AND SOME LIGHT MARINE
LAYER SHOWERS COULD ALSO DEVELOP EACH DAY.

AVIATION...

WIDESPREAD IFR CIGS EXTEND WELL INTO CENTRAL TEXAS WITH SOME DRYING
MOVING SE FROM ARKANSAS. GENERAL TROUGHING OVER TEXAS TODAY MAY KEEP
ANY IMPROVEMENTS SLOW TO OCCUR. WILL INDICATE SOME OPTIMISM FOR KBTR
AND KMCB WITH MVFR CIGS AROUND 15Z THEN VFR BY 18Z. THE CLEARING
LINE MAY REACH KHDC BUT WILL THEN RETURN NORTHWARD AS MVFR CIG IN
RESPONSE TO VORTICITY MAXIMUM PASSING OVER AREA TONIGHT. REMAINING
LOCATIONS WILL LIKELY REMAIN IFR FOR MUCH OF THE MORNING BEFORE
IMPROVING TO LOW END MVFR CIGS THEN PERSISTING AT MVFR LEVELS FOR
REMAINDER OF TAF VALID PERIOD. 24/RR

MARINE...

SURFACE LOW PRESSURE AREA WAS BROADENING AND BECOME INVERTED OPEN
WAVE OVER THE NORTH-CENTRAL GULF. LOW LEVEL COLD AIR ADVECTION HAS
BROUGHT SOME HIGHER GUSTINESS OVER THE NEAR SHORE WATERS THAT SHOULD
SPREAD SOUTHWARD THROUGH THE MORNING BEFORE EASING BY MID-AFTERNOON.
WILL ISSUE A SMALL CRAFT ADVISORY FOR THE COASTAL WATERS IN EFFECT
WITH PACKAGE ISSUANCE THROUGH 21Z PACKAGE ISSUANCE. TIDAL LAKES ARE
A CLOSE CALL AS SOME GUSTINESS IS IN THE 15-20KT RANGE CURRENTLY BUT
THIS SHOULD RELAX SHORTLY TO PRECLUDE ANY HEADLINES AFTER 3 AM.
WINDS WILL VEER STEADILY TO ONSHORE FLOW BY MONDAY AND INCREASE TO
MODERATE LEVELS TUESDAY IN ADVANCE OF STRONG COLD FRONT APPROACH.
SMALL CRAFT ADVISORY LEVEL WINDS ARE POSSIBLE ON RETURN FLOW BY LATE
TUESDAY MORNING THEN HIGH END SMALL CRAFT ADVISORY LEVELS WITH
FREQUENT GALE FORCE GUSTS AFTER FRONTAL PASSAGE TUESDAY EVENING INTO
WEDNESDAY MORNING. WINDS AND SEAS SHOULD REMAIN AT MODERATE TO
STRONG LEVELS FOR CHRISTMAS MORNING...SETTLING TO SOMEWHAT LOWER
LEVELS CHRISTMAS AFTERNOON. 24/RR

DECISION SUPPORT...

DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
             CITY OF NEW ORLEANS DSS 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  56  39  61  45 /  10  10  10  10
BTR  59  43  64  48 /  10  10  20  20
ASD  57  44  62  48 /  20  20  30  20
MSY  57  50  62  53 /  20  20  30  20
GPT  56  47  62  51 /  20  30  30  30
PQL  57  45  63  48 /  30  30  30  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 3 PM SATURDAY FOR THE FOLLOWING
     ZONES: BRETON SOUND...CHANDELEUR SOUND...COASTAL WATERS
     FROM BOOTHVILLE LA TO THE SOUTHWEST PASS OF THE MISSISSIPPI
     RIVER OUT 20 NM...COASTAL WATERS FROM PASCAGOULA MS TO
     STAKE ISLAND LA FROM 20 TO 60 NM...COASTAL WATERS FROM
     PASCAGOULA MS TO STAKE ISLAND LA OUT 20 NM...COASTAL WATERS
     FROM PORT FOURCHON TO LOWER ATCHAFALAYA RIVER FROM 20 TO 60
     NM...COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA
     RIVER OUT 20 NM...COASTAL WATERS FROM STAKE ISLAND LA TO
     THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60
     NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON FROM 20 TO 60
     NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON OUT 20 NM...LAKE
     BORGNE...AND MISSISSIPPI SOUND.

MS...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 3 PM SATURDAY FOR THE FOLLOWING
     ZONES: BRETON SOUND...CHANDELEUR SOUND...COASTAL WATERS
     FROM BOOTHVILLE LA TO THE SOUTHWEST PASS OF THE MISSISSIPPI
     RIVER OUT 20 NM...COASTAL WATERS FROM PASCAGOULA MS TO
     STAKE ISLAND LA FROM 20 TO 60 NM...COASTAL WATERS FROM
     PASCAGOULA MS TO STAKE ISLAND LA OUT 20 NM...COASTAL WATERS
     FROM PORT FOURCHON TO LOWER ATCHAFALAYA RIVER FROM 20 TO 60
     NM...COASTAL WATERS FROM PORT FOURCHON TO LOWER ATCHAFALAYA
     RIVER OUT 20 NM...COASTAL WATERS FROM STAKE ISLAND LA TO
     THE SOUTHWEST PASS OF THE MISSISSIPPI RIVER FROM 20 TO 60
     NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON FROM 20 TO 60
     NM...COASTAL WATERS FROM THE SOUTHWEST PASS OF THE
     MISSISSIPPI RIVER TO PORT FOURCHON OUT 20 NM...LAKE
     BORGNE...AND MISSISSIPPI SOUND.

&&

$$







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