379  
FXUS64 KLIX 212111  
AFDLIX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NEW ORLEANS LA  
411 PM CDT SAT APR 21 2018  
   
SHORT TERM
 
 
AN UPPER LOW AND ASSOCIATED SHORTWAVE TROUGH WILL MOVE EAST-  
SOUTHEAST ACROSS THE SOUTHERN PLAINS TONIGHT AND EASTWARD OVER  
WESTERN ARKANSAS BY SUNDAY MORNING. SURFACE LOW WAS OVER CENTRAL  
TEXAS. AN ASSOCIATED WARM FRONT EXTENDED SOUTHEAST FROM THE LOW TO  
THE TEXAS COAST TO NORTH CENTRAL GULF. THIS LOW WILL ADVECT IN  
LOW LEVEL MOISTURE. SURFACE DEWPOINT OF 65F WILL PUSH NORTH TO  
1-20 AND 70F SOUTH OF TIDAL LAKES FROM 12Z TO 18Z SUNDAY. A WARM  
FRONTAL BOUNDARY WILL PUSH NORTH AND SHOULD CROSS THE WESTERN TO  
CENTRAL GULF COAST REGION BY LATER TONIGHT. 0-3KM HELICITY VALUES  
ARE EXPECTED TO INCREASE 250 TO 350M/S JUST AHEAD OF THE WARM  
FRONT 10 TO 15Z SUNDAY ACROSS THE FLORIDA PARISHES AND SOUTHERN  
MISSISSIPPI. THESE HIGHER VALUES WILL SHIFT NORTHEAST AS THE WARM  
FRONT SHIFTS NORTH OF THE FORECAST BY NOON SUNDAY. THEREFORE, THE TINY  
WINDOW OF ATMOSPHERE CONDUCIVE FOR ROTATING STORMS WILL SHIFT  
NORTH AS INSTABILITY ARRIVES A LITTLE BEHIND THE WARM FRONT.  
THEREFORE, THE MAIN THREAT WILL BE GUSTY WINDS FROM STRONG STORMS  
SUNDAY MORNING.  
 
THE ORIENTATION OF THE UPPER LEVEL LOW MAINTAIN THE COLD CORE  
NORTH OF THE FORECAST AND HAIL THREAT IS LOW. THE COLD FRONT IS  
EXPECTED TO MOVE THROUGH THE FORECAST AREA SUNDAY AFTERNOON AND  
EVENING, SO RAIN CHANCES SHOULD DIMINISH AS THE FRONT MOVES  
THROUGH WITH ONLY A FEW LINGERING SHOWERS EXPECTED (MAINLY IN  
NORTHERN AND EASTERN AREAS) SUNDAY EVENING. ENTRAINMENT OF DRY AIR  
ON THE SOUTH SIDE OF THE LOW WILL QUICKLY DISPLACE THE MOISTURE  
EAST SUNDAY EVENING, DECREASING RAIN CHANCES TO NIL AFTER 06Z  
SUNDAY.  
   
LONG TERM
 
 
SERIES OF SHORTWAVE TROUGHS IN THE LARGER LONGWAVE TROUGH OVER  
THE EASTERN U.S. ARE EXPECTED TO MOVE SOUTHEAST FROM THE NORTHERN  
PLAINS AND UPPER MISSISSIPPI VALLEY ACROSS THE MID TO LOWER  
MISSISSIPPI VALLEY AND SOUTHEAST STATES THROUGH THE MIDDLE TO LATE  
PART OF THE WEEK. SOME MODEL DIFFERENCES STILL EXIST FROM RUN TO  
RUN CONSISTENCY WITH TIMING, STRENGTH AND ORIENTATION OF THESE  
SYSTEMS AS THEY MOVE ACROSS THE LOWER MISSISSIPPI VALLEY. BECAUSE  
OF THIS, THERE IS LOW CONFIDENCE IN EXACTLY WHICH PERIODS WILL  
EXPERIENCE MENTIONABLE CHANCES OF RAINFALL. THEREFORE WILL  
MAINTAIN A SLIGHT CHANCE TO CHANCE OF SHOWERS IS ON TUESDAY  
ACROSS SOUTHEAST MISSISSIPPI, WEDNESDAY AND WEDNESDAY NIGHT ACROSS  
ALL BUT THE SOUTHERN COASTAL AREAS, AND ON FRIDAY WHEN A MORE  
POTENT STORM SYSTEM COULD MOVE THROUGH THE CENTRAL GULF COAST  
REGION. TEMPERATURES ARE EXPECTED TO BE GENERALLY SLIGHTLY BELOW  
THE SEASONAL AVERAGES. 18  
 

 
   
AVIATION
 
 
LOWERING LIFTED CONDENSATION LEVELS ASSOCIATED WITH DEEPER  
MOISTURE ADVECTING IN FROM THE GULF OF MEXICO SHOULD PUSH CEILINGS  
INTO MVFR RANGE OF 2000 TO 3000 FEET. FURTHER LOWERING OF  
CEILINGS TO AROUND 1500 TO 2000 FEET IS EXPECTED TO OCCUR AFTER  
00Z. ADDITIONALLY, HAVE INCLUDED A MENTION OF VICINITY SHOWERS IN  
THE FORECAST FOR ALL OF THE TERMINALS BY 05Z. AFTER 06Z,  
PREVAILING SHOWERS AND MVFR AND IFR VISIBILITIES ARE FORECAST FOR  
KBTR, KMCB, KHDC, KHUM, AND KMSY. FURTHER TO THE EAST, VFR  
VISIBILITIES SHOULD CONTINUE THROUGH 12Z AS THE BAND OF RAIN  
REMAINS WEST OF KASD, KGPT, AND POSSIBLY KNEW. AT KMSY, VCTS  
WORDING WILL BE ADDED AFTER 12Z.  
 

 
   
MARINE
 
 
TIGHT PRESSURE GRADIENT OVER THE COASTAL WATERS ALLOWED SOUTHEAST WINDS  
TO INCREASE TO 15 TO 20 KNOTS THIS AFTERNOON. WINDS WILL DECREASE  
SLIGHTLY THIS EVENING ONLY TO INCREASE BACK TO 15 TO 20 KNOTS OVER  
THE COASTAL WATERS SUNDAY. AS A RESULT, EXERCISE CAUTION FLAGS  
WILL BE RAISED AGAIN. ONLY THE TIDAL LAKES ARE EXPECTED TO REMAIN  
BELOW EXERCISE CAUTION LEVELS.  
 
A PASSING COLD FRONT SUNDAY EVENING WILL SHIFT WINDS TO THE  
NORTHWEST. A DECREASE IN THE OVERALL PRESSURE GRADIENT OVER THE  
NORTHERN GULF SHOULD ALLOW WINDS TO RELAX BACK TO 10 TO 15 KNOTS  
SUNDAY NIGHT. NEXT WEEK SHOULD SEE A PERSISTENT OFFSHORE FLOW OF  
AROUND 10 TO 15 KNOTS FROM MONDAY THROUGH THE END OF THE WEEK AS A  
SERIES OF WEAK REINFORCING FRONTS SLIDES THROUGH THE WATERS. 18  
 

 
   
DECISION SUPPORT
 
 
DSS CODE: BLUE.  
DEPLOYED: NONE.  
ACTIVATION: NONE.  
ACTIVITIES: ASSESSING THUNDERSTORM RISK FOR SUNDAY  
SANDHILL CRANE NWR OUTREACH SUPPORT  
NEW ORLEANS NAVY WEEK SUPPORT  
 
DECISION SUPPORT SERVICES (DSS) CODE LEGEND  
GREEN = NO WEATHER IMPACTS THAT REQUIRE ACTION.  
BLUE = LONG-FUSED WATCH, WARNING, OR ADVISORY IN EFFECT OR HIGH  
VISIBILITY EVENT; MARGINAL RISK SEVERE OR EXCESSIVE RAIN.  
YELLOW = HEIGHTENED IMPACTS WITH SHORT-FUSED WATCH, WARNING OR  
ADVISORY ISSUANCES; RADAR SUPPORT FOR SLIGHT RISK SEVERE OR  
EXCESSIVE RAIN.  
ORANGE = HIGH IMPACTS; ENHANCED RISK SEVERE; NEARBY TROPICAL EVENTS;  
HAZMAT OR OTHER LARGE EPISODES.  
RED = FULL ENGAGEMENT FOR MODERATE TO HIGH RISK OF SEVERE AND/OR  
EXCESSIVE RAINFALL; DIRECT TROPICAL THREATS; EVENTS OF  
NATIONAL SIGNIFICANCE.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
MCB 63 74 54 70 / 60 90 10 10  
BTR 64 78 54 73 / 70 90 10 0  
ASD 63 75 58 74 / 40 90 20 0  
MSY 66 77 58 74 / 40 90 10 0  
GPT 66 73 60 73 / 30 90 30 0  
PQL 64 74 59 73 / 30 90 30 0  
 

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

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab LA Page
The Nexlab MS Page Main Text Page