Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 290601 AAC AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 201 AM EDT FRI AUG 29 2014 .UPDATE... ISSUED AT 150 AM EDT FRI AUG 29 2014 A RIDGE OF HIGH PRESSURE CENTERED OVER THE SOUTHEASTERN CONUS EXTENDED NORTH AND NORTHWEST INTO THE APPALACHIANS AND THE OH VALLEY REGION. AT THE SFC HIGH PRESSURE WAS CENTERED OVER THE GREAT LAKES REGION. MEANWHILE...A BOUNDARY IS STALLED OUT FROM SOUTHEAST VA SOUTH INTO THE APPALACHIANS AND EAST TN AND THEN NORTHWEST TO LOW PRESSURE OVER THE PLAINS STATES. SOME PASSING CIRRUS AND MID LEVEL CLOUDS ARE MOVING ACROSS THE REGION AT THIS POINT AROUND THE RIDGE...ESPECIALLY THE FAR WEST AND THE NORTH. THIS TREND IS EXPECTED TO CONTINUE OVERNIGHT WITH THE SFC HIGH TO OUR NORTHEAST AND THE UPPER RIDGE DOMINATING. HOURLY TEMPS...DEWPOINTS AND WINDS WERE FRESHENED UP BASED ON THE RECENT OBSERVATION DATA. SOME AREAS OF VALLEY FOG HAVE FORMED OR ARE EXPECTED TO FORM OVERNIGHT...AND MIGHT BECOME DENSE IN A COUPLE OF SPOTS. HOWEVER... IT SHOULD NOT BECOME WIDESPREAD. UPDATE ISSUED AT 1006 PM EDT THU AUG 28 2014 UPDATED AGAIN TO BLEND LATEST OBS INTO THE FORECAST GRIDS...WITHOUT ANY SIGNIFICANT CHANGE TO THE OVERALL FORECAST. UPDATE ISSUED AT 711 PM EDT THU AUG 28 2014 UPDATED TO BLEND LATEST OBS INTO THE FORECAST GRIDS...WITHOUT ANY SIGNIFICANT CHANGE TO THE OVERALL FORECAST. && .SHORT TERM...(THIS EVENING THROUGH FRIDAY NIGHT) ISSUED AT 331 PM EDT THU AUG 28 2014 SURFACE HIGH PRESSURE CURRENTLY REIGNS FROM THE GREAT LAKES INTO THE OHIO VALLEY. BROAD LOW PRESSURE CENTERED ACROSS THE PLAINS HAS A WARM FRONT BRANCHED OUT TO THE ESE...BECOMING MORE STATIONARY AND ILL- DEFINED ACROSS SOUTHERN KENTUCKY. ALOFT...AN UPPER LEVEL RIDGE AXIS REMAINS POISED ACROSS THE MISSISSIPPI VALLEY...WITH AN UPPER LOW/TROUGH CRUISING INTO THE PLAINS. CONVECTION HAS POPPED UP ALONG THE STATIONARY BOUNDARY...MAINLY ACROSS THE SOUTHWESTERN PORTION OF THE COMMONWEALTH...WHERE BETTER INSTABILITY HAS BUILT UP DURING THE AFTERNOON. SO FAR...ONLY A FEW SHOWERS HAVE DOTTED PORTIONS OF THE CUMBERLAND VALLEY WITHIN EASTERN KENTUCKY. THE MODELS ARE IN GOOD AGREEMENT THROUGH THE SHORT TERM...WITH THE UPPER LEVEL RIDGE AMPLIFYING AND SHIFTING EAST WITH TIME AS THE UPPER TROUGH DAMPENS AND RIDES NORTHEAST ACROSS THE PLAINS...REACHING NEAR THE GREAT LAKES REGION BY EARLY SATURDAY MORNING. THIS WILL KEEP PLENTY OF HEAT AND HUMIDITY ACROSS EASTERN KENTUCKY INTO THE START OF THE HOLIDAY WEEKEND...WITH THE THREAT OF SOME ISOLATED CONVECTION... MAINLY DURING THE FAVORED AFTERNOON AND EARLY EVENING HOURS. ANY ISOLATED SHOWERS AND A STRAY THUNDERSTORM WILL WIND DOWN QUICKLY THROUGH EARLY THIS EVENING AS WE LOSE INSTABILITY. FOG WILL LIKELY SET IN ONCE AGAIN...ALTHOUGH IT SHOULD BE MORE RESTRICTED TO THE VALLEYS COMPARED TO LAST NIGHT. OVERNIGHT LOWS WILL GENERALLY RANGE FROM THE LOW TO MID 60S. FOR FRIDAY...HIGH TEMPERATURES WILL APPROACH THE 90 DEGREE MARK...WITH ISOLATED CONVECTION THREATENING DURING THE AFTERNOON AND EVENING HOURS. FRIDAY NIGHT WILL FEATURE A MORE BALMY NIGHT...WITH VALLEY FOG AND LOWS IN THE MID TO UPPER 60S FOR MOST. .LONG TERM...(SATURDAY THROUGH THURSDAY) ISSUED AT 331 PM EDT THU AUG 28 2014 THE EXTENDED WILL BEGIN WITH A BROAD BUT WEAKENING RIDGE OF HIGH PRESSURE PARKED OVER THE SOUTHEASTERN CONUS ON SATURDAY. AT THE SAME TIME...THE MODELS HAVE A RATHER POTENT LOW PRESSURE SYSTEM ALOFT APPROACHING FROM THE PLAINS. THE FRONT TRAILING FROM THIS SYSTEM WILL PROVIDE OUR NEXT GOOD CHANCE OF RAIN SATURDAY NIGHT INTO SUNDAY. THE PRIMARY CONCERNS WITH THIS NEXT WEATHER PATTERN WILL BE THE LARGE AMOUNTS OF GULF MOISTURE THAT ARE LIKELY TO STREAM INTO THE TENNESSEE AND OHIO VALLEY REGIONS...AND THE SLOWNESS OF THE FRONT TO EXIT THE AREA. BASED ON THE CURRENT DATA...THE FRONT SHOULD STALL OUT ACROSS THE AREA THROUGH MONDAY NIGHT. A SECOND MUCH LESS WELL DEFINED BOUNDARY WILL THEN AFFECT THE AREA ON THE HEELS OF THE ORIGINAL FRONT FROM THE WEEKEND. THE ISSUE WITH THE SECOND BOUNDARY IS TIMING AND MOISTURE AVAILABILITY...WHICH THE GFS AND ECMWF WERE HANDLING QUITE DIFFERENTLY. IN FACT...DURING THE MIDDLE OF THE WEEK...THE ECMWF STALLS OUT ANOTHER FRONT ACROSS THE AREA...WITH AMPLE MOISTURE INTERACTING WITH THE BOUNDARY. THE GFS...HOWEVER...KEEPS ITS BOUNDARY MOSTLY TO OUR NORTH...ALONG WITH MOST OF THE MOISTURE ASSOCIATED WITH IT. THAT BEING SAID...THE ECMWF SOLUTION WAS USED FOR SYSTEM EVOLUTION AND PRECIPITATION COVERAGE AND AMOUNTS FROM SATURDAY THROUGH MONDAY NIGHT. AFTER THAT...A BLEND OF THE TWO MODELS WAS USED TO CREATE THE NEW FORECAST...WITH LOWER THAN MEXMOS VALUES FOR POPS EACH OF THOSE DAYS AND NIGHTS DO TO THE UNCERTAINTY. THE BEST TIME FRAME FOR RAIN LOOKS TO BE SATURDAY NIGHT THROUGH MONDAY NIGHT DUE TO THE STALLED FRONT. THERE WILL ALSO BE THE POTENTIAL FOR LOCALLY HEAVY RAINFALL TO START THE PERIOD AS THE LATEST FORECAST SOUNDINGS ARE PREDICTING BETWEEN 1.8 TO JUST OVER 2 INCHES OF PRECIPITABLE WATER AND A TALL SKINNY CAPE PROFILE. THIS WILL BEAR WATCHING OVER THE NEXT COUPLE OF DAYS. BASED ON THIS TYPE OF INSTABILITY PROFILE...THE POTENTIAL FOR THUNDERSTORM ACTIVITY SHOULD BE A LITTLE LESS THAN WE HAVE SEEN OVER THE PAST WEEK OR SO. TEMPERATURES THROUGHOUT MOST OF THE PERIOD LOOK TO BE SLIGHTLY WARMER THAN NORMAL DUE TO PERSISTENT SOUTHERLY FLOW ASSOCIATED WITH EACH OF THE PASSING WEATHER SYSTEMS AND THE LARGE AMOUNT OF WARM MOIST AIR THAT WILL BE TRANSPORTED INTO THE AREA OFF THE GULF OF MEXICO. HIGHS EACH DAY WILL AVERAGE IN THE MID TO UPPER 80S...WITH OVERNIGHT LOWS BOTTOMING OUT AROUND 70. THE ONE EXCEPTION TO THIS RULE WOULD BE SUNDAY...WHICH SHOULD SEE COOLER THAN NORMAL TEMPERATURES DUE TO THE EXTENSIVE CLOUD AND LONG LASTING PRECIPITATION THAT IS EXPECTED. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT) ISSUED AT 158 AM EDT FRI AUG 29 2014 IFR OR WORSE FOG IS EXPECTED TO DEVELOP LATE TONIGHT NEAR VALLEYS OF LARGE STREAMS. THE FOG WILL DISSIPATE BY AROUND 13Z FRIDAY...LEAVING PREVAILING VFR. AT THE TAF SITES...MAINLY MVFR FOG IS EXPECTED FOR A FEW HOURS BETWEEN ABOUT 8Z AND 13Z. THIS MIGHT DROP INTO THE IFR RANGE AT SJS FOR A COUPLE OF HOURS AROUND 11Z. OTHERWISE...ONCE THE FOG DISSIPATES... ISOLATED THUNDERSTORMS ARE EXPECTED AFTER 16Z...AS A BOUNDARY CURRENTLY STALLED OUT TO OUR SOUTH RETURNS NORTH AS WARM FRONT. VIS AND OR CIGS COULD DROP BRIEFLY TO IFR OR LOWER IN ANY LOCATION THAT IS DIRECTLY AFFECTED BY ANY TSRA. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...GEOGERIAN LONG TERM...AR AVIATION...JP

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