FXUS62 KJAX 131851 AFDJAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSONVILLE FL 251 PM EDT FRI APR 13 2007 .SHORT TERM...CHAMBER OF COMMERCE DAY WITH SUNNY SKIES AND TEMPS CURRENTLY IN THE 70S...EXCEPT LOW 80S FROM GAINESVILLE SOUTHWARD. ALOFT...FLATTENING RIDGE EXTENDS OVER THE SOUTHEAST STATES...WITH VIGOROUS TROUGH OVER THE LOWER ROCKIES. AT SURFACE...BELT OF SURFACE HIGHS EXTEND FROM UPPER PLAINS TO THE SOUTHEAST STATES... WITH DEEPENING LOW OVER TEXAS PANHANDLE. TRANQUIL CONDITIONS WILL CONTINUE TONIGHT WITH MEAN LAYER RIDGE MAINTAINING ITS GRIP OVER THE REGION. THIS COUPLED WITH A WEAK ONSHORE FLOW WILL LIKELY LEAD TO PATCHES OR POSSIBLE AREAS OF FOG DEVELOPMENT OVERNIGHT TONIGHT...ESPECIALLY ACROSS OUR EASTERN ZONES WHERE DEWPOINTS WILL BE HIGHEST. SATURDAY WILL BE A TRANSITION DAY AS MEAN LAYER RIDGE EXITS EAST DURING THE EARLY MORNING HOURS. VIGOROUS STORM SYSTEM WILL INITIALLY IMPACT LARGE PORTION OF MISSISSIPPI VALLEY REGION DURING THE MORNING HOURS...THEN IMPACTING OHIO VALLEY AND TENNESSEE VALLEY REGIONS AS WELL AS WESTERN PORTION OF SOUTHEAST UNITED STATES DURING THE AFTERNOON. THE PRESSURE GRADIENT BETWEEN DEPARTING HIGH AND APPROACHING LOW WILL INCREASE SOUTHERLY GRADIENT ACROSS JAX CWA...WITH SUSTAINED WINDS OF 15 TO 25 MPH ESTABLISHING BY LATE MORNING OR EARLY AFTERNOON. THESE WINDS WILL LIKELY PROMPT LAKE WIND ADVISORY FOR OUR AREA. IN ADDITION...THESE WINDS WILL DRIVE AFTERNOON TEMPS INTO MID TO UPPER 80S...WITH POCKETS OF AROUND 90 POSSIBLE ACROSS OUR SOUTHERN-MOST INTERIOR AREAS. THERE IS STILL SOME UNCERTAINTY WHEN PRECIP WILL INITIATE ACROSS OUR LOCAL AREA...WITH 12Z GUIDANCE GENERALLY DELAYING PRECIP UNTIL LATE SATURDAY AFTERNOON/EVENING. HAVE BACKED OFF ON PRECIP COVERAGE/TIMING IN RESPONSE TO THIS...WITH ISOLATED CONVECTION POSSIBLY REACHING OUR WESTERN-MOST ZONES LATE IN THE AFTERNOON. MAIN FORECAST CHALLENGE THROUGH THE SHORT-TERM WILL BE PRECIP COVERAGE AND TYPE FOR SATURDAY NIGHT AND INTO SUNDAY. SURFACE LOW IS FORECAST TO FURTHER DEEPEN AS IT ADVANCES ACROSS NORTH GEORGIA SATURDAY EVENING...REACHING THE CAROLINAS LATE SATURDAY NIGHT. THIS WILL ENABLE A TRAILING COLD FRONT TO APPROACH THE LOCAL AREA AFTER MIDNIGHT. AHEAD OF THIS SURFACE FRONT...STRONG LOW-LEVEL JET (SOUTHWEST WINDS OF 50 KNOTS OR GREATER) WILL IMPACT THE LOCAL AREA. THIS SCENARIO WOULD QUICKLY DE-DESTABILIZE THE ATMOSPHERE ACROSS THE LOCAL AREA AS THESE WINDS QUICKLY BRING INFLUX OF MOISTURE FROM THE GULF OF MEXICO. IN ADDITION...NUMERICAL MODELS CONTINUE TO SUGGEST LARGE PRESSURE RISES BEHIND THE FRONT DUE TO STRONG NVA/SUBSIDENCE WORKING IN. THUS...THERE REMAINS THE LIKELIHOOD OF SQUALL LINE (SOME TYPE OF ORGANIZED LINE OF CONVECTION) INITIATING ACROSS OUR WESTERN- MOST ZONES LATE SATURDAY NIGHT (AFTER MIDNIGHT)...WITH EASTWARD PROGRESSION THROUGH SUNDAY MORNING. THIS FEATURE (IF REALIZED) WOULD LIKELY CLEAR OUR SOUTHEAST COUNTIES BY MID-MORNING ON SUNDAY. THE MAIN CONCERN REMAINS DAMAGING STRAIGHT-LINE WINDS...WITH POTENTIAL FOR HAIL DUE TO COOLING OF UPPER LEVELS OF THE ATMOSPHERE...AS WELL AS POSSIBILITY OF ISOLATED TORNADOES EMBEDDED WITHIN MAIN LINE. SQUALL LINE WILL BE CLOSELY FOLLOWED BY SURFACE COLD FRONT...WITH RAINS ENDING FROM WEST WITH FRONTAL PASSAGE. STRONG WESTERLY WINDS OF 20 TO 30 MPH WILL LIKELY ESTABLISH AT THE SURFACE BY MID- MORNING...AND BOSTON TECHNIQUE IS CURRENTLY SUGGESTING WIND GUSTS UPWARDS OF 40 MPH. THIS WILL LIKELY PROMPT ISSUANCE OF WIND ADVISORY FOR JAX CWA. MUCH COOLER AND DRIER CONDITIONS ARE EXPECTED INTO EARLY NEXT WEEK... WITH COLDEST READINGS EXPECTED MONDAY MORNING...WITH UPPER 30S POSSIBLE ACROSS OUR WESTERN-MOST ZONES. .LONG TERM (TUE THRU FRI)...HIGHLY AMPLIFIED YET PROGRESSIVE PATTERN WILL BEGIN THE EXTENDED PERIOD WITH CLOSED LOWS OVER NEW ENGLAND STATES AND 4 CORNERS REGION AND RIDGE OVER THE CENTRAL PLAINS. THESE FEATURES COUPLED WITH SURFACE HIGH TO OUR WEST WILL BRING DRY AND COOL CONDITIONS UNDER NORTHWEST FLOW. WEDNESDAY... MEAN LAYER RIDGE WILL ESTABLISH OVER THE REGION AS UPSTREAM LOW APPROACHES THE CENTRAL PLAINS. THIS WILL MAINTAIN DRY AND STABLE CONDITIONS ACROSS THE LOCAL AREA. NEXT CHANCE FOR RAINS WILL ARRIVE WEDNESDAY WHEN MEAN LAYER RIDGE EXITS EAST AND UPSTREAM WEATHER SYSTEM WILL WEAKEN WHILE TRAVERSING THE LOCAL AREA. DRY AND STABLE CONDITIONS WILL YET AGAIN RETURN TO THE AREA THURSDAY AND FRIDAY. && .AVIATION...VFR THIS EVE...WITH TEMPO MVFR OVER THE AREA BETWEEN 08Z AND 13Z SAT DUE TO INCREASING MOISTURE. && .MARINE...HAVE POSTED A SCA BEGINNING SATURDAY AFTERNOON. WILL PROBABLY NEED A GALE WARNING EITHER LATE SATURDAY NIGHT OR SUNDAY MORNING BUT BEING IT IS STILL SEVERAL PERIODS AWAY WILL LET NEXT SHIFT ISSUE IT AS THE EXACT TIMING OF THIS EVENT BECOMES MORE CLEAR. NO HEADLINES FOR TONIGHT. AS STRONG COLD FRONT APPROACHES THE AREA...SOUTH WINDS WILL RAPIDLY INCREASE BY AFTERNOON. AS THE STRONG LOW LEVEL JET AND SQUALL LINE MOVES ACROSS THE WATERS LATE SATURDAY NIGHT OR SUNDAY AM WILL PROBABLY AT LEAST SEE FREQUENT GUSTS TO GALE FORCE. WINDS SHIFT TO WEST SUNDAY WITH PROBABLE FREQUENT GUSTS AS LOW PRESSURE TO THE NORTH FURTHER INTENSIFIES. HAVE CONTINUED WITH PREVIOUS MARINE WEATHER STATEMENT. && .FIRE WEATHER...RED FLAGS IN EFFECT FOR ALL AREAS...EXCEPT THE IMMEDIATE COAST. HAVE WENT AHEAD AND POSTED A FIRE WEATHER WATCH FOR BOTH SATURDAY AND SUNDAY AFTERNOONS. RH'S WILL BE MARGINAL BUT WINDS WILL BE STRONG WITH HIGH DISPERSION LEVELS EXPECTED ESP SAT AFTERNOON. && .PRELIMINARY POINT TEMPS/POPS... AMG 52 87 63 67 / 10 20 70 50 SSI 60 80 66 72 / 10 10 70 60 JAX 57 87 66 74 / 10 10 60 60 SGJ 61 86 67 75 / 10 10 60 70 GNV 56 88 66 74 / 10 10 60 60 OCF 57 87 66 75 / 0 10 60 60 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...RED FLAG WARNING UNTIL 8 PM EDT THIS EVENING FOR ALACHUA-BAKER- BRADFORD-CLAY-COLUMBIA-DUVAL-FLAGLER-GILCHRIST-HAMILTON- MARION-NASSAU-PUTNAM-ST JOHNS-SUWANNEE-UNION. FIRE WEATHER WATCH SATURDAY AFTERNOON FOR ALACHUA-BAKER- BRADFORD-CLAY-COLUMBIA-DUVAL-FLAGLER-GILCHRIST-HAMILTON-MARION- NASSAU-PUTNAM-ST JOHNS-SUWANNEE-UNION. FIRE WEATHER WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING FOR ALACHUA-BAKER-BRADFORD-CLAY-COLUMBIA-DUVAL-GILCHRIST- HAMILTON-MARION-NASSAU-PUTNAM-ST JOHNS-SUWANNEE-UNION. GA...RED FLAG WARNING UNTIL 7 PM EDT THIS EVENING FOR APPLING- ATKINSON-BACON-BRANTLEY-CHARLTON-CLINCH-COFFEE-ECHOLS-JEFF DAVIS-PIERCE-WARE-WAYNE. AM...SMALL CRAFT ADVISORY FROM 4 PM SATURDAY TO 8 AM EDT TUESDAY FOR ALTAMAHA SOUND GA TO FERNANDINA BEACH FL 20 NM TO 60 NM OFFSHORE-FERNANDINA BEACH TO ST AUGUSTINE FL 20 NM TO 60 NM OFFSHORE-ST AUGUSTINE TO FLAGLER BEACH FL 20 NM TO 60 NM OFFSHORE. SMALL CRAFT ADVISORY FROM 4 PM SATURDAY TO 11 PM EDT MONDAY FOR ALTAMAHA SOUND GA TO FERNANDINA BEACH FL OUT 20 NM- FERNANDINA BEACH TO ST AUGUSTINE FL OUT 20 NM-ST AUGUSTINE TO FLAGLER BEACH FL OUT 20 NM. && $$ ZAPPE/PETERSON