Issued by NWS New Orleans/Baton Rouge, LA
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000 FXUS64 KLIX 210125 AFDLIX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW ORLEANS LA 725 PM CST FRI NOV 20 2009 .UPDATE... ...SOUNDING DISCUSSION... NO PROBLEMS WITH THE FLIGHT THIS EVENING. MOISTURE CREEPING BACK EVER SO SLOWLY WITH A PW UP TO 0.91 INCHES. STILL PLENTY OF DRY AIR BELOW 700 MILLIBARS BUT A VERY MOIST SOUNDING ABOVE THAT LAYER. RAINFALL AMOUNTS WILL LIKELY BE ONLY SPRINKLES AND VERY LIGHT SHOWERS UNTIL THE LOWER LAYERS BECOME MOIST. WINDS ARE LIGHT AND VARIABLE IN THE LOWEST LEVELS AND FROM THE SOUTHWEST ALOFT. && .PREV DISCUSSION... /ISSUED 327 PM CST FRI NOV 20 2009/ SHORT TERM... ADVANCING HIGH CLOUD DECK A RESULT OF LARGE CONVECTIVE FLARE-UP IN THE WEST GULF THIS MORNING THAT HAS SINCE MOVED INTO THE MID-GULF AND WEAKENED DURING THE PAST FEW HOURS. LARGE UPPER LEVEL DIVERGENCE STRUCTURE WITH ADVANCING LOW PRESSURE TROUGH SWINGING ACROSS LOWER TEXAS. PRESSURE FALLS NOTED ALONG THE LOWER TEXAS COAST VICINITY OF BROWNSVILLE FOR WHAT APPEARS TO BE CYCLOGENESIS. MEANWHILE...HIGH PRESSURE THAT WAS SETTLED OVER THE SOUTEASTERN U.S. HAS WEAKENED AND RETREATED NORTHWARD...THEREBY SOFTENING THE GRADIENT MORE THAN PREVIOUSLY EXPECTED FROM EARLIER MODEL RUNS. GENERALLY FOLLOWING CONTINUITY OF PAST FORECASTS AND SOMEWHAT IN LINE WITH GFS. BIGGEST UNCERTAINTIES LIE WITH FUTURE TRACK OF SURFACE LOW...WHICH MAY BE MUCH FARTHER SOUTH THAN ANY MODELS ARE INDICATING WITH WAKE DEPRESSION HEIGHT FALLS BEHIND CONVECTIVE COMPLEX IN GULF CARVING A MORE APT TRAJECTORY THAN MODEL INDICATED. IF SUCH IS THE CASE...THEN MOST OF THE LAND AREAS WILL BE SUBJECTED TO ISENTROPIC LIFT STRATIFORM AND ELEVATED CONVECTION FOR A DURATION OF 12 TO 18 HOURS ONSETTING AROUND MIDNIGHT IN THE WEST AND EXITING THE EAST AROUND SATURDAY LATE AFTERNOON. THE BULK OF SURFACE BASED CONVECTION SHOULD REMAIN OVER MARINE AREAS BUT TRENDS WILL HAVE TO BE MONITORED CLOSELY OVERNIGHT AND PARTICULARLY SATURDAY MORNING. CURRENT AMBIENT CONDITIONS ARE RATHER DRY AND CONTINENTALLY INFLUENCED SO THE SATURATION PROCESS FROM TOP-DOWN WILL BE A RATHER SLOW ONE. AFTER LOW PRESSURE PASSAGE SATURDAY...HIGH PRESSURE SHOULD BUILD INTO THE REGION AND MAINTAIN A LONG STRETCH OF SEASONABLY COOL TO MILD TEMPERATURES. LONG TERM... SEASONABLY COOL TO MILD TEMPERATURES AND GENERALLY RAIN FREE DAYS ARE IN STORE EXCEPT FOR A BRIEF SHOT AT ISOLATED SHOWERS TUESDAY WITH THE PASSAGE OF RE-ENFORCING COLD FRONT. MOISTURE DOES APPEAR TO BE LIMITED WITH THIS SYSTEM. THANKSGIVING TRAVEL SHOULD BE DEVOID OF ANY WEATHER DELAYS ACROSS THE FORECAST AREA. AVIATION... VFR CONDITIONS SHOULD PERSIST AT TERMINALS THRU 00Z. SFC LOW OVER THE NWRN GULF WILL CONTINUE ON AN ENE TRACK TOWARDS THE AREA. HIGH LEVEL CLOUDS WILL PROGRESSIVELY INCREASE OVER THE NEXT FEW HOURS. RAIN SHIELD FROM THIS FEATURE REMAINS SW OF THE AREA BUT WILL GRADUALLY MOVE IN TONIGHT AN INTO TOMORROW MORNING. CIGS WILL DROP TO MOSTLY MVFR BY DAYBREAK BUT POSSIBLY LOWER WITH CLUSTERS OF STRONGER SHOWERS. WINDS WILL SLOWLY TRANSITION FROM ENE TO NNE BY THE END OF THE PERIOD. MEFFER MARINE... TRENDS WITH SURFACE PRESSURE GRADIENT WILL HAVE TO BE MONITORED NEXT 12 HOURS BUT DOES APPEAR TO BE HOLD AROUND THE 15-20 KT RANGE AS LONG AS THE LOW PRESSURE SYSTEM DOES NOT DEEPEN MUCH FURTHER THAN 1010MB UPON APPROACH. A PERIOD OF HIGHER GUSTS IN THE 25 TO 30 KT RANGE MAY BE POSSIBLE SATURDAY LATE MORNING BUT NOT HIGHLY CONFIDENT GIVEN THE WEAKEING GRADIENT. WILL POST A`SMALL CRAFT EXERCISE CAUTION` HEADLINE VALID AFTER 00Z FOR THE COASTAL AREAS AT THIS TIME WITH THE POSSIBILITY OF SMALL CRAFT ADVISORIES IF CONDITIONS EXCEED EXPECTATIONS. AFTER LOW PASSES...SOME ENHANCED WINDS DUE TO SHORT DURATION COLD AIR ADVECTION INTO SUNDAY...THEN FLATTENING OUT FOR MUCH OF NEXT WEEK. FRONTAL PASSAGE ON TUESDAY DOES NOT APPEAR TO HAVE MUCH IMPACT ON COASTAL AREAS OTHER THAN TO RE-ENFORCE HIGH PRESSURE ALREADY IN PLACE. && .PRELIMINARY POINT TEMPS/POPS... MCB 48 58 46 64 / 60 80 40 10 BTR 50 59 47 67 / 80 80 20 10 MSY 55 63 52 66 / 80 80 20 10 GPT 53 63 52 64 / 40 90 40 10 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...NONE. GM...NONE. MS...NONE. GM...NONE. && $$
