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

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755
FXUS64 KLIX 222122
AFDLIX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
322 PM CST SAT NOV 22 2014

.DISCUSSION...
MAIN FORECAST CHALLENGE CONTINUES TO BE NAILING DOWN TIMING AND
EXTENT OF ANY SEVERE WEATHER LATE TONIGHT AND SUNDAY MORNING.
OVERALL FORECAST THINKING HAS NOT CHANGED AND GENERALLY ONLY SMALL
TWEAKS WERE MADE TO THE FORECAST WITH THIS PACKAGE.

BASE OF TROUGH DIGGING INTO NORTHERN MEXICO IS CLEARLY INDICATED
ON WV IMAGERY. SURFACE LOW IS BEGINNING TO TAKE SHAPE OVER WEST
TEXAS. LARGE AREA OF SHOWERS AND THUNDERSTORMS NOTED OVER CENTRAL
AND EAST TEXAS WITH A FEW WARNINGS ALREADY BEING ISSUED THIS
AFTERNOON.

UPPER TROUGH AND ASSOCIATED SURFACE FEATURES WILL MOVE EASTWARD
THIS EVENING AND TONIGHT. AS THE UPPER TROUGH MOVES INTO THE LOWER
MISSISSIPPI VALLEY...IT IS EXPECTED TO TAKE ON A SLIGHT NEGATIVE
TILT. GFS AND EURO ARE A BIT MORE AGGRESSIVE DEVELOPING A JET
STREAK ON THE EAST SIDE OF THE TROUGH AND ENHANCING LIFT ACROSS
THE AREA. PW VALUES ARE ON THE RISE AND MODEL FORECAST SOUNDING
STILL INDICATE THAT PW VALUES SHOULD BE AROUND 1.75 INCHES BY THIS
EVENING. 00Z BALLOON DATA WILL GIVE A GOOD INDICATION IF THIS
MOISTENING IS OCCURRING.

LOOKS LIKE THE MAIN LIMITING FACTOR WILL BE INSTABILITY AS BEST
CAPE VALUES ARE FORECAST TO REMAIN OVER THE GULF. GFS IS MOST
AGGRESSIVE BRINGING 500 TO 1000 J/KG ML CAPE INTO THE SOUTHERN
HALF OF THE FORECAST AREA BETWEEN 06Z AND 12Z. NAM AND EURO
INDICATE MAX ML CAPE OVER LAND AROUND 500 J/KG AND THAT WILL ONLY
BE NEAR THE COAST. THIS COULD KEEP STRONGEST THUNDERSTORMS JUST
OFF SHORE. ANOTHER CONSIDERATION WILL BE WHETHER ONGOING
CONVECTION OVER THE GULF WILL CUT OFF INFLOW OVER LAND AREAS.

THAT BEING SAID...THERE ARE STILL PLENTY OF PARAMETERS THAT WOULD
SUPPORT SEVERE THUNDERSTORMS IF SURFACE BASED INSTABILITY CAN BE
REALIZED OVER LAND AREAS. SR HELICITY PEAKS IN THE 400 TO 600
M2/S2 RANGE ACROSS A LARGE PORTION OF THE AREA DEPENDING ON
LOCATION AND MODEL OF CHOICE...SO ROTATING UPDRAFTS WILL BE A
POSSIBILITY...ESPECIALLY IF ANY DISCRETE CELLS DEVELOP AHEAD OF
THE MAIN SQUALL LINE.

THE MAIN SEVERE WEATHER THREAT WILL ARRIVE WITH THE SQUALL LINE
AND WHILE ALL MODES OF SEVERE WEATHER WILL BE POSSIBLE...DAMAGING
WIND GUSTS ALONG THE LEADING EDGE OF THE LINE WILL BE MOST LIKELY.
AGAIN...WITH STRONG HELICITY...SOME EMBEDDED ROTATING CELLS WILL
BE POSSIBLE. MAIN THREAT TIMING LOOKS TO BE LATE TONIGHT AND
SUNDAY MORNING.

CURRENT THINKING IS THAT THE SQUALL LINE SHOULD BE CLEAR OF THE
LOCAL AREA BY ABOUT NOON WITH ONLY A SLIGHT CHANCE OF SHOWERS
DURING THE AFTERNOON HOURS.

COLD FRONT WILL HOLD OFF UNTIL LATE SUNDAY NIGHT OR MONDAY
MORNING. COOLER AND DRIER AIR WILL MOVE IN BEHIND THE FRONT...BUT
AIR MASS BEHIND THE FRONT IS NOT NEARLY AS COLD AS THE LAST TWO
FRONTS. IN FACT...WHILE TEMPS WILL DROP BELOW NORMAL...AM CURRENTLY
NOT FORECASTING ANY FREEZING TEMPERATURES FOR THE LOCAL AREA
THROUGH THE PERIOD.

&&

.AVIATION...
CONDITIONS ARE GRADUALLY EXPECTED TO DETERIORATE TO MVFR TO IFR
THIS EVENING INTO TONIGHT AND SUNDAY MORNING AS A STORM SYSTEM
APPROACHES THE AREA. RAIN AND THUNDERSTORMS ARE EXPECTED TO BECOME
WIDESPREAD OVER THE AIRPORTS ALONG AND WEST OF I-55 BETWEEN 06Z-
12Z SUNDAY AND ELSEWHERE BETWEEN 10Z-16Z. STRONG TO SEVERE TSRA
MAY BECOME WIDESPREAD AND ORGANIZED ENOUGH TO HAVE A HIGH
PROBABILITY OF GUSTS 35 TO 40 KNOTS AS A SQUALL LINES MOVES
THROUGH...SO HAVE ADDED A 4 HOUR TEMPO GROUP WITH THESE GUSTS
ALONG WITH LOWER VSBYS AND CIGS DURING THE PERIOD OF TSRA.

&&

.MARINE...
WINDY CONDITIONS OVER ALL OF THE WATERS. A DEEPENING SFC LOW WILL
MOVE FROM ERN TX THROUGH THE ARKLAMISS AND INTO WRN TENNESSEE THIS
EVENING THROUGH SUNDAY. THIS WILL KEEP THE WINDS STRONG THROUGH
SUNDAY WITH PREVAILING ONSHORE FLOW. THE PERSISTENT STRONG ONSHORE
FLOW WILL ALSO LEAD TO HIGHER THAN NORMAL TIDES THIS EVENING AND
TONIGHT. NUMEROUS SHOWERS AND THUNDERSTORMS WILL IMPACT THE MARINE
ZONES THROUGH SUNDAY MORNING. A COLD FRONT WILL FINALLY MOVE
THROUGH ON MONDAY AND AS THIS HAPPENS WINDS WILL GET ANOTHER
SURGE BACK INTO SCY CRITERIA. MODERATE TO STRONG OFFSHORE WILL
REMAIN OVER THE REGION TUE THROUGH MUCH OF NEXT WEEK.

&&

.DECISION SUPPORT...
DSS CODE...BLUE.
DEPLOYED...NONE.
ACTIVATION...NONE.
ACTIVITIES...SLURRY SUPPORT
             SMALL CRAFT ADVISORIES
             COASTAL FLOOD ADVISORY
             ENHANCED RISK OF SEVERE

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  60  74  53  64 /  80 100  10  10
BTR  62  76  53  64 /  90  90  10  10
ASD  62  76  55  66 /  80 100  10  10
MSY  64  77  57  66 /  80 100  10  10
GPT  63  75  57  67 /  70 100  10  10
PQL  62  75  57  68 /  70 100  20  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...COASTAL FLOOD ADVISORY UNTIL 6 AM SUNDAY FOR THE FOLLOWING
     ZONES: LOWER PLAQUEMINES...LOWER ST.
     BERNARD...ORLEANS...AND UPPER ST. BERNARD.

MS...COASTAL FLOOD ADVISORY UNTIL 6 AM SUNDAY FOR THE FOLLOWING
     ZONES: AND HANCOCK.

GM...SMALL CRAFT ADVISORY UNTIL 6 PM SUNDAY 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...LAKE PONTCHARTRAIN AND LAKE MAUREPAS...AND
     MISSISSIPPI SOUND.

&&

$$

AVIATION...22/TD
MARINE...CAB
REST OF DISCUSSION...95/DM





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