Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 301151 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 751 AM EDT SAT AUG 30 2014 .UPDATE... ISSUED AT 735 AM EDT SAT AUG 30 2014 HOURLY GRIDS HAVE BEEN FRESHENED UP BASED ON RECENT OBSERVATIONS. ANY LINGERING RIVER VALLEY FOG SHOULD LIFT AND DISSIPATE THROUGH 9 AM EDT. OTHERWISE...MOISTURE WILL INCREASE FROM THE SOUTH AND SOUTHWEST TODAY AND CLOUD COVER WILL ALSO...ESPECIALLY FROM LATE MORNING INTO THE AFTERNOON. DAYTIME HEATING AND AN APPROACHING DISTURBANCE WILL LEAD TO AT LEAST ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS BY MID TO LATE AFTERNOON AND CONTINUING INTO THE EVENING. RECENT HRRR RUNS AS WELL AS THE RECENT GFS AND NAM RUNS SUPPORT THIS. && .SHORT TERM...(TODAY THROUGH SUNDAY) ISSUED AT 415 AM EDT SAT AUG 30 2014 AN ILL DEFINED WARM FRONT IS GRADUALLY LIFTING NORTH AND NORTHEAST ACROSS THE NORTHERN AND EASTER PART OF THE REGION. CONVECTION FROM EARLIER IN THE OVERNIGHT HOURS DISSIPATED...BUT SOME MID CLOUDS ARE LEFT BEHIND ACROSS THOSE AREAS. PATCHY VALLEY FOG HAS DEVELOPED IN A FEW SPOTS EARLY THIS MORNING...BUT VIS REDUCTIONS HAVE NOT BEEN ALL THAT MUCH. AT MID AND UPPER LEVELS...A RIDGE OF HIGH PRESSURE IS CENTERED OVER THE SOUTHEASTERN CONUS WITH A TROUGH EXTENDING SOUTH FROM THE UPPER MIDWEST TO THE MS VALLEY REGION BETWEEN THE SOUTHEAST RIDGE AND RIDGING OVER THE DESERT SOUTHWEST. A SHORTWAVE WAS ALSO LOCATED OVER EAST TX/WESTERN LA EARLY THIS MORNING. THIS PATTERN PUTS THE REGION IN DEEP SOUTHERLY TO SOUTHWESTERLY FLOW WITH EMBEDDED PASSING SHORTWAVES. THE TROUGH WILL GRADUALLY WORK INTO THE GREAT LAKES REGION AND LOWER OH VALLEY REGION TODAY AND INTO TONIGHT...AND PICK UP THE SOUTHERN SHORTWAVE AND SEND IT INTO THE TN AND LOWER OH VALLEY REGION BY LATE TONIGHT AND THEN SLOWLY ACROSS THE AREA ON SUNDAY. THE DEEP SOUTHERLY FLOW WILL BRING A PLUME OF VERY DEEP MOISTURE NORTH INTO THE OH AND TN VALLEY REGION LATER TONIGHT AND LINGERING INTO THE DAY ON SUNDAY. PWS ARE PROGGED TO CLIMB TOWARD TWO INCHES BY LATE THIS EVENING AND LINGER NEAR THAT LEVEL INTO SUNDAY EVENING. HOWEVER...THE DEEPER MOISTURE WILL START TO DECREASE LATE IN THE PERIOD AS THE DISTURBANCE BEGINS TO EXIT. AFTER ANY EARLY MORNING VALLEY FOG DISSIPATES WITHIN A COUPLE HOURS AFTER SUNSET...A PERIOD OF SUNSHINE WITH SOME MID AND HIGH LEVEL CLOUDS IS ANTICIPATED FOR MUCH OF THE MORNING...AND LINGERING INTO THE EARLY AFTERNOON ACROSS THE FAR NORTHEAST. CONVECTION WITH SHORTWAVE WORKING TOWARD THE LOWER OH VALLEY REGION SHOULD DEVELOP OR APPROACH THE SOUTHWESTERN AND SOUTHERN PARTS OF THE AREA BY EARLY TO MID AFTERNOON. ADDITIONAL CONVECTION WILL BE POSSIBLE AS DAYTIME HEATING OF THE INCREASINGLY MOIST AIR MASS OCCURS. THE MOISTURE INCREASE SHOULD OCCUR FIRST ACROSS THE SOUTH AND WEST...SO CHANCES FOR CONVECTION LATER TODAY WILL BE BEST IN THOSE AREAS. DRIER AIR AND AN INITIAL DOWNSLOPE COMPONENT TO THE WINDS WILL LESSEN CHANCES FOR CONVECTION ACROSS THE FAR EAST AND SOUTHEAST. AS THE SHORTWAVE(S) TRACK INTO KY...THE CHANCES FOR CONVECTION WILL INCREASE ACROSS THE JKL CWA TONIGHT AS THEY INTERACT WITH THE DEEP MOISTURE IN PLACE. THIS SCENARIO WILL BE INSTABILITY AND UPPER LEVEL DRIVEN AND POSSIBLY MESOSCALE DRIVEN FROM OUTFLOWS WITH NO REAL SFC FEATURES. THE PW WILL BE AROUND THE 99TH PERCENTILE SO ANY THUNDERSTORM IS EXPECTED TO HAVE HIGH RAINFALL RATES IF CONVECTION WERE TO TRAIN OR MOVE REPEATEDLY ACROSS THE SAME LOCATIONS HEAVY RAIN AND HIGH WATER WOULD BE A CONCERN. THE MODEL CONSENSUS STILL FOCUS THE BEST CHANCES FOR RAIN TONIGHT ACROSS THE WEST AND NORTHWEST. THE TRACK OF THE SHORTWAVE(S) THEN BRINGS THE FOCUS FOR CONVECTION A BIT FURTHER SOUTH AND EAST ON SUNDAY. OVERALL...QPF FOR THE EVENT SHOULD BE HIGHEST ACROSS THE WEST AND NORTH...AND ON AVERAGE THE LEAST NEAR THE VA BORDER. ABOVE NORMAL TEMPERATURES ARE EXPECTED AGAIN TODAY...WITH TEMPS NEARING 90 AGAIN IN SOME LOCATIONS...ESPECIALLY NORTH AND EAST. THE INCREASE IN CLOUD COVER SHOULD KEEP THE SOUTHWESTERN LOCATIONS NEAR THE SAME...IF NOT A BIT COOLER THAN THE REST OF THE AREA TODAY. CLOUD COVER AND THE DEEP MOISTURE WILL LEAD TO ABOVE NORMAL MIN TEMPS TONIGHT. HOWEVER...WITH ANTICIPATED CLOUD COVER...TEMPERATURES SHOULD AVERAGE NEAR NORMAL...IT NOT A BIT BELOW NORMAL ON SUNDAY WHERE SHOWERS AND THUNDERSTORMS ARE THE MOST PERSISTENT. .LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY) ISSUED AT 241 AM EDT SAT AUG 30 2014 MODELS ARE IN OK AGREEMENT INTO THE EARLY PART OF THE WEEK...BUT DIFFERENCES EMERGE AROUND A COLD FRONT DROPPING IN FROM THE NORTH AROUND MIDWEEK. THESE DIFFERENCES MAINLY REVOLVE AROUND TIMING AND EXACTLY WHERE THE BOUNDARY STALLS OR ENDS UP BY WEDNESDAY. THUS...FORECAST CONFIDENCE IS DIMINISHED BEYOND MONDAY. HOWEVER...AS IT LOOKS NOW...PRECIPITATION CHANCES THROUGH NEXT WEEK WILL HAVE A DIURNAL TREND...PEAKING IN THE LATE AFTERNOON HOURS...WITH A MINIMUM OVERNIGHT. STARTING OFF SUNDAY NIGHT...PRECIPITATION WITH THE SHORTWAVE TROUGH ON SUNDAY WILL COME TO AN END SUNDAY EVENING...WITH THE AREA DRYING OUT OVERNIGHT. NOT MUCH ON TAP FOR MONDAY WITH LACK OF ANY SUBSTANTIAL SYSTEM. WE WILL PROBABLY JUST SEE A FEW ISOLATED SHOWERS OR STORMS POP UP DURING THE AFTERNOON...BUT COVERAGE SHOULD BE VERY LOW. SAME WILL HOLD FOR TUESDAY...ALTHOUGH THE AFOREMENTIONED COLD FRONT MAY ARRIVE FROM THE NORTH IF THE GFS IS CORRECT LATE IN THE DAY. THE ECMWF IS SLOWER AND HOLDS THE FRONT TO OUR NORTH THROUGH THE DAY. BY TUESDAY NIGHT AND WEDNESDAY THE COLD FRONT SHOULD MAKE ITS WAY ACROSS THE AREA. SHOWER/STORM COVERAGE ALONG THE FRONT MAY BE TIED MORE TO AVAILABLE INSTABILITY...WITH THE HIGHEST COVERAGE TUESDAY EVENING AND AGAIN WEDNESDAY AFTERNOON/EVENING. HOWEVER...AGAIN CONFIDENCE IS LOW AS THE GFS TAKES THE BOUNDARY SOUTH OF US AND WOULD SUPPORT DRIER WEATHER FOR TUESDAY NIGHT AND WEDNESDAY. NO SUBSTANTIAL SYSTEMS THROUGH THE REMAINDER OF THE EXTENDED...BUT GIVEN THE WARMTH AND HUMIDITY...ISOLATED SHOWERS/STORMS WILL BE POSSIBLE EACH AFTERNOON/EVENING THROUGH THE END OF THE WEEK. TEMPERATURES WILL REMAIN NEAR OR SLIGHTLY ABOVE NORMAL THROUGH THE WHOLE WEEK. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING) ISSUED AT 750 AM EDT SAT AUG 30 2014 ANY LINGERING VALLEY FOG WILL DISSIPATE EARLY IN THE PERIOD BY 13Z OR SO...BUT WILL NOT AFFECT THE TAF SITES. CLOUDS WILL ALSO BE ON THE INCREASE DURING THE DAY OUT AHEAD OF AN APPROACHING UPPER LEVEL SYSTEM. THE CONVECTIVE THREAT ASSOCIATED WITH THIS SYSTEM LOOKS TO HOLD OFF UNTIL 18Z OR LATER...WHEN VCTS WAS INCLUDED IN THE TAFS. ANY OF THIS COULD BRING A PERIOD OF IFR AS THEY PASS. SHRA AND SOME TSRA MAY BECOME MORE WIDESPREAD LATER IN THE PERIOD TOWARD 0Z OR LATER. ONCE THE ATMOSPHERE SATURATES THE LOWEST LEVELS...SOME MVFR WILL BE POSSIBLE AND VIS MAY BE REDUCED TO MVFR OR LOWER. HOWEVER CONFIDENCE IN THIS WAS TOO LOW TO INCLUDE ATTM. WINDS WILL AVERAGE OUT OF THE SOUTH TO SOUTHWEST AT 5 TO 10 KT OR LESS DURING THE PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...JP LONG TERM...KAS AVIATION...JP

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