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

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FXUS64 KLIX 211253
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
653 AM CST SUN DEC 21 2014

...SOUNDING DISCUSSION...

A LITTLE DRIER AIR HAS WORKED INTO THE ENVIRONMENT SINCE THE
PREVIOUS TWO BALLOON LAUNCHES WITH THE PRECIPITABLE WATER VALUE
DOWN TO 0.70 INCHES. THE LOW LEVELS ARE RATHER MOIST AGAIN...BUT
NOT TO THE EXTENT THEY WERE YESTERDAY MORNING. THE TOP OF THE
MOIST LAYER IS CHARACTERIZED BY A 1 DEGREE CELSIUS INCREASE PER
100 FEET BETWEEN 5500 AND 5800 FEET. WINDS WERE VARIABLE BELOW
3000 FEET. GENERALLY ABOVE THIS LEVEL WINDS WERE FROM THE
SOUTHWEST. A PEAK WIND SPEED OF 113 KNOTS WAS LOCATED AT 40000
FEET.

12Z BALLOON INFO: A ROUTINE FLIGHT THIS MORNING LASTING 101 MINUTES
AND REACHING A HEIGHT OF 19.7 MILES ABOVE THE GROUND BURSTING JUST
NORTHWEST OF MOBILE 95 MILES DOWNRANGE FROM THE OFFICE.

ANSORGE

&&

.PREV DISCUSSION... /ISSUED 409 AM CST SUN DEC 21 2014/

SHORT TERM...

A SERIES OF WEAK VORTICITY MAXIMA WILL SLIDE ACROSS THE AREA ON
THE BACK OF A STRONG 110 KNOT JET STREAK PARKED OVER THE GULF
COAST. THE AREA WILL BE IN A FAVORABLE REGION FOR INCREASED UPPER
LEVEL OMEGA. HOWEVER...THE OVERALL ATMOSPHERE WILL REMAIN VERY DRY
WITH PW VALUES GENERALLY RUNNING AROUND 0.75 INCHES.
THUS...RAINFALL IS NOT EXPECTED OVER MOST OF THE LAND BASED ZONES
TODAY. HOWEVER...A STATIONARY FRONT WILL REMAIN IN PLACE OVER THE
NORTHERN GULF OF MEXICO. THIS FRONTAL BOUNDARY WILL SERVE AS A
FOCUS FOR SOME SCATTERED TO NUMEROUS SHOWERS FOR THE OFFSHORE
COASTAL WATERS AND IMMEDIATE COASTAL AREAS OF LOUISIANA. THESE
SHOWERS WILL BE PRODUCED BY A REGION OF WEAK ISENTROPIC FORCING
ALONG AND NORTH OF THE BOUNDARY THAT WILL BE AIDED BY THE
INCREASING OMEGA ALOFT ASSOCIATED WITH A PASSING VORT LOBE. WITH
MORE CLOUD COVER IN PLACE ALONG THE COAST...TEMPERATURES WILL
REMAIN COOLER IN THESE AREAS. HOWEVER...INLAND LOCATIONS WILL SEE
TEMPERATURES CLIMB BACK TO MORE NORMAL LEVELS FOR LATE DECEMBER
WITH READINGS RISING INTO THE LOWER 60S.

TONIGHT...THERE WILL BE INCREASING LOW LEVEL MOISTURE ACROSS THE
AREA AS WINDS VEER FROM THE NORTHEAST TO THE SOUTHEAST. OVERALL
BOUNDARY LAYER FLOW WILL BE VERY LIGHT...AND SOME AREAS OF FOG
COULD DEVELOP AWAY FROM THE TIDAL LAKES AND COAST. HAVE INCLUDED A
MENTION OF FOG IN THE GRIDS FOR LATE TONIGHT AND EARLY TOMORROW
MORNING. SOME OF THE FOG COULD TURN DENSE AT TIMES AROUND
DAYBREAK. OUTSIDE OF THE FOG THREAT...CONDITIONS WILL REMAIN
FAVORABLE FOR OFFSHORE SHOWERS AS A STATIONARY BOUNDARY LINGERS
OVER THE NORTHERN GULF. OVERALL RAIN CHANCES WILL BE LOWER
TOMORROW AS OVERALL OMEGA ALOFT DECREASES IN THE WAKE OF A
DEPARTING VORT LOBE...AND DO NOT EXPECT THE SHOWERS TO PERSIST
OVER THE IMMEDIATE LOUISIANA COAST TOMORROW. AS A RESULT...A DRY
FORECAST IS IN PLACE FOR ALL LAND BASED ZONES TOMORROW...EXCEPT
FOR AREAS IN THE IMMEDIATE VICINITY OF HEAD OF PASSES IN LOWER
PLAQUEMINES PARISH. WITH ONSHORE FLOW AND INCREASING MOISTURE IN
PLACE...ALONG WITH LESS OVERALL CLOUD COVER TEMPERATURES WILL
EASILY RISE INTO THE UPPER 60S AND LOWER 70S TOMORROW AFTERNOON.

A MAJOR PATTERN CHANGE WILL BEGIN TO IMPACT THE REGION TOMORROW
NIGHT AS AN UPPER LEVEL TROUGH CENTERED OVER THE PLAINS BEGINS TO
RAPIDLY DEEPEN. THIS RAPID DEEPENING WILL BE DRIVEN BY SOME STRONG
NORTHERN STREAM VORTICITY DESCENDING DOWN THE SPINE OF THE
ROCKIES. AN ATTENDANT UPPER LEVEL JET IN EXCESS OF 120 KNOTS WILL
ACCOMPANY THIS NORTHERN STREAM FEATURE AS IT DIVES INTO TEXAS. AS
THIS JET ROUNDS THE BASE OF THE TROUGH...IT WILL BEGIN TO TAKE ON
A MORE NEUTRAL TILT AND ALSO START TO LIFT TO THE NORTHEAST. A
STRONG COLD FRONT WILL BE FOUND OVER CENTRAL TEXAS BY DAYBREAK ON
TUESDAY...AND AS THE JET STREAK ROUNDS THE BASE OF THE
TROUGH...LOW LEVEL CYCLOGENESIS WILL BEGIN IN EASTERN TEXAS.

THIS DEVELOPING LOW WILL FORCE THE LINGERING BOUNDARY OVER THE
NORTHERN GULF OF MEXICO NORTHWARD LATE MONDAY NIGHT. MODELS
INDICATE THAT VERY STRONG OMEGA WILL DEVELOP ACROSS THE FORECAST
AREA DUE TO THE COMBINATION OF INCREASED ISENTROPIC FORCING IN
THE LOW LEVELS...AND THE DEVELOPMENT OF A JET COUPLET OVER THE
GULF SOUTH IN THE UPPER LEVELS. WITH AMPLE LIFT AND INCREASING
INSTABILITY IN PLACE...EXPECT TO SEE RAINFALL DEVELOP IN THE LATE
EVENING HOURS AND BECOME MORE LIKELY AS THE NIGHT PROCEEDS. MODEL
SOUNDINGS INDICATE THAT A STABLE LAYER WILL CONTINUE TO EXIST IN
THE LOW LEVELS...BUT THAT AMPLE ELEVATED CAPE EXISTS ABOVE 900MB.
HAVE KEPT IN A MENTION OF THUNDER FOR AREAS ALONG AND NORTH OF THE
I-10 CORRIDOR WHERE OVERALL OMEGA IS EXPECTED TO GREATEST. THERE
COULD BE SOME STRONGER CONVECTION LATE MONDAY NIGHT GIVEN THE
DECENT LAPSE RATES ALOFT WITH HAIL BEING THE PRIMARY THREAT.

TUESDAY WILL BE A VERY ACTIVE DAY...WITH A FAIRLY DECENT THREAT
FOR SOME SEVERE WEATHER EXISTING. THE STRONG UPPER LEVEL TROUGH
WILL BECOME NEGATIVELY TILTED OVER THE SOUTHERN PLAINS AND OZARKS
BY TUESDAY EVENING AND START TO QUICKLY LIFT TO THE NORTHEAST ON
THE BACK OF A STRONG 120 KNOT JET STREAK. AS THE UPPER LEVEL
TROUGH BEGINS TO LIFT OUT...THE SURFACE LOW IN TEXAS WILL TRACK
ACROSS LOUISIANA AND MISSISSIPPI AND FORCE A STRONG COLD FRONT
THROUGH THE AREA TUESDAY EVENING INTO TUESDAY NIGHT.

THE REGION WILL REMAIN CENTERED BENEATH A JET COUPLET AND
OVERALL UPPER LEVEL FORCING WILL BE VERY STRONG. 700MB OMEGA
VALUES WILL BE IN EXCESS -25MB/S OVER MOST OF THE AREA. THESE
VALUES ARE VERY SUPPORTIVE OF DEEP AND SUSTAINED UPDRAFTS IN ANY
CONVECTION THAT DOES DEVELOP. IN ADDITION...OVERALL INSTABILITY
WILL INCREASE THROUGH THE DAY...AS DAYTIME HIGHS RISE INTO THE
LOWER TO MIDDLE 70S AND LAPSE RATES ALOFT REMAIN DECENT. CAPE
VALUES SHOULD RISE TO AROUND 1000 J/KG AND LIFTED INDICES WILL
INCREASE TO AROUND -4. THUS...THERE WILL BE LITTLE IN THE WAY OF
CONVECTIVE INHIBITION THROUGH THE DAY. SHEAR VALUES WILL ALSO BE
FAIRLY IMPRESSIVE WITH 0-3 KM SHEAR 30-40 KNOTS IN THE AFTERNOON
AND EVENING HOURS. DIRECTIONAL SHEAR WILL BE SOMEWHAT LIMITED...AND
OVERALL HELICITY VALUES WILL PEAK OUT AROUND 150 M2/S2. GIVEN THESE
PARAMETERS...THE THREAT FOR TORNADOES WILL BE SOMEWHAT
REDUCED...AND THE THREAT FOR STRONG STRAIGHT LINE WINDS WILL BE
INCREASED. HOWEVER...ALL CONVECTIVE MODES WILL BE POSSIBLE WITH
THIS SYSTEM THROUGHOUT THE DAY ON TUESDAY AND INTO EARLY TUESDAY
NIGHT. MOST OF THE CONVECTION WILL LIKELY BE PRE-FRONTAL...WITH
THE MAIN WIND SHIFT AND SURGE OF COLDER AIR GENERALLY COMING IN
LATE TUESDAY EVENING OVER WESTERN ZONES AND DURING THE LATE OVERNIGHT
HOURS FOR EASTERN ZONES. CONDITIONS WILL CLEAR FROM WEST TO EAST
WITH THIS FRONTAL PASSAGE...AND EXPECT TO SEE LINGERING CONVECTION
AND A THREAT FOR ISOLATED SEVERE THUNDERSTORM ACTIVITY OVER THE
COASTAL MISSISSIPPI ZONES THROUGH LATE TUESDAY NIGHT. TEMPERATURES
WILL BE A GOOD 10 DEGREES COOLER OVER MOST AREAS TUESDAY
NIGHT...BUT THE MAIN SURGE OF COLDER AIR WILL NOT REALLY BE FELT
UNTIL DURING THE DAY ON WEDNESDAY.

LONG TERM...

THE UPPER LEVEL TROUGH AXIS WILL PASS THROUGH THE AREA WEDNESDAY
AND WEDNESDAY NIGHT. THE HEART OF THE COLD POOL WILL ALSO PASS
OVER THE AREA DURING THIS TIME FRAME. 1000-500MB THICKNESSES WILL
PLUNGE TO AROUND 5430 METERS AND 925MB TEMPERATURES WILL DROP TO
AROUND 0 DEGREES CELSIUS BY WEDNESDAY AFTERNOON. THIS CORRELATES
TO A SURFACE TEMPERATURE IN THE LOWER 50S. WITH CLEAR SKIES IN
PLACE WEDNESDAY NIGHT...READINGS WILL EASILY COOL INTO THE 30S
OVER MOST AREAS. A LIGHT FREEZE MAY OCCUR OVER PARTS OF SOUTHWEST
MISSISSIPPI AND THE NORTHSHORE LATE WEDNESDAY NIGHT. CONDITIONS
WILL ALSO BE VERY BREEZY AS THE TROUGH AXIS MOVES THROUGH WEDNESDAY
INTO WEDNESDAY NIGHT.

THE TROUGH AXIS WILL FINALLY BEGIN TO PULL EAST OF THE AREA ON
THURSDAY...WITH STRONG SUBSIDENCE AND VERY DRY AIR TAKING HOLD OF
THE AREA. SUNNY SKIES AND COOLER THAN NORMAL TEMPERATURES CAN BE
EXPECTED. DAYTIME HIGHS WILL ONLY CLIMB INTO THE MIDDLE TO UPPER
50S AND LOWS ON THURSDAY NIGHT WILL DROP BACK INTO THE LOWER 40S
OVER INLAND LOCATIONS AS CONDITIONS RADIATE OUT.

BOTH THE EURO AND THE GFS INDICATE THAT ANOTHER SHORT WAVE TROUGH
WILL SLIDE THROUGH THE AREA FOR FRIDAY AND SATURDAY. THE EURO HAS
A SHARPER TROUGH SLIDE THROUGH THE AREA...AND THUS SPARKS OFF MORE
RAINFALL OVER THE AREA. THE GFS HAS A SHALLOWER TROUGH THAT BRINGS
INCREASING CLOUDS...BUT LOWER OVERALL POPS TO THE REGION FOR
FRIDAY AND SATURDAY. AT THIS TIME...HAVE MADE LITTLE CHANGE TO THE
FORECAST AND WILL KEEP A SLIGHT CHANCE OF POPS AND CLOUDY SKIES
OVER THE AREA FOR FRIDAY AND SATURDAY. A FRONTAL BOUNDARY SHOULD
SLIDE THROUGH THE AREA DURING THE DAY ON SATURDAY. WEAK ONSHORE
FLOW AND SOME WARM AIR ADVECTION IN ADVANCE OF THE BOUNDARY SHOULD
ALLOW TEMPERATURES TO RISE BACK INTO THE MIDDLE TO UPPER 60S ON
SATURDAY.

AVIATION...

A BRIEF IMPROVEMENT TO VFR CAVOK CONDITIONS MADE IT AS FAR AS
KMCB-KHDC-KBTR LINE BUT HAS RETREATED NORTH WITH GENERALLY MVFR CIGS
REPORTED AT ALL BUT KMCB. MVFR CONDITIONS SHOULD PREVAIL FOR MUCH OF
THE TAF PERIOD WITH SOME BRIEF IMPROVEMENT TO VFR BASED CIGS AROUND
SUNSET. MARINE LAYER ADVECTION ONSET AFTER 22/02Z TO BRING MVFR CIGS
BACK INTO TERMINALS FOR OVERNIGHT HOURS. SOME RADIATIONAL FOG MAY
BRING VSBYS TO MVFR LEVELS AT THE MORE INTERIOR LOCATIONS GENERALLY
AFTER 09Z. 24/RR

MARINE...

FRINGE OF CONTINENTAL HIGH PRESSURE AREA EXTENDS INTO THE CENTRAL
GULF AND THE GRADIENT SHOULD RELAX THROUGHOUT THE DAY. THE HIGH
MOVES EAST OVERNIGHT WITH SHORT-FETCHED ONSHORE FLOW DEVELOPING
MONDAY IN ADVANCE OF DEVELOPING FRONTAL SYSTEM IN THE PLAINS STATES.
ONSHORE FLOW BECOMES DEEPER AND LONGER FETCHED MONDAY NIGHT TO BRING
INCREASE IN WINDS AND SEAS AT SMALL CRAFT ADVISORY LEVELS BY LATE
TUESDAY INTO TUESDAY NIGHT. FRONTAL PASSAGE STILL LOOKS TO BRING
HARD WIND SHIFT WITH STRONG COLD AIR ADVECTION WEDNESDAY FOR HIGH
END SMALL CRAFT ADVISORY WINDS WITH LOW END GALE GUSTS. CONDITIONS
IMPROVE STEADILY HEADING INTO THURSDAY AS CENTER OF HIGH BECOMES
SETTLED OVER THE NORTH GULF. 24/RR

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  61  46  68  59 /   0   0   0  50
BTR  62  48  69  60 /   0   0   0  50
ASD  62  48  69  59 /  10  10   0  50
MSY  61  53  69  61 /  10  10   0  50
GPT  61  51  69  61 /  10  10  10  40
PQL  63  49  71  61 /  10  10  10  40

&&

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

$$







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