Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 181532 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 1132 AM EDT THU SEP 18 2014 .UPDATE...
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ISSUED AT 1132 AM EDT THU SEP 18 2014 UPDATED TO REMOVE THE LAST OF THE FOG AS IT IS JUST NOW FINISHING UP BURNING OFF ACROSS SOME OF OUR EASTERN AREAS. THIS HAS SLOWED DOWN THE TEMPERATURE RISE THIS MORNING SOME...BUT WE SHOULD NOT HAVE A PROBLEM CATCHING BACK UP WITH AMPLE SUNSHINE INTO THIS AFTERNOON. OTHERWISE...OUTSIDE OF THESE TWEAKS TO THE TEMPERATURES...NO SIGNIFICANT CHANGES MADE AT THIS TIME. UPDATE ISSUED AT 745 AM EDT THU SEP 18 2014 RADAR TRENDS INDICATE THAT THE SPRINKLES AND STRAY LIGHT SHOWERS HAVE BEEN GRADUALLY DIMINISHING SINCE A LITTLE BEFORE SUNRISE ACROSS THE REGION. SOME DENSE FOG IS STILL OCCURRING ON A COUPLE OF RIDGETOP LOCATIONS...MAINLY IN THE BIG SANDY REGION. OTHERWISE...MID LEVEL CLOUDS SHOULD CONTINUE TO MOVE ACROSS THE REGION THIS MORNING...WITH CU DEVELOPMENT POSSIBLE IN THE AFTERNOON. HOURLY GRINDS HAVE BEEN UPDATED BASED ON RECENT OBSERVATIONS AND TRENDS. AN UPDATED ZFP IS ALREADY OUT.
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&& .SHORT TERM...(TODAY THROUGH FRIDAY) ISSUED AT 400 AM EDT THU SEP 18 2014 A MID LEVEL DISTURBANCE CONTINUES TO NEAR THE LOWER OH VALLEY REGION THIS MORNING. THIS DISTURBANCE HAS BROUGHT SOME MID LEVEL MOISTURE AND BANDS OF MID LEVEL CLOUDS TO THE COMMONWEALTH. THESE BANDS OF CLOUDS DO HAVE SOME THIN SPOTS AND HOLES IN THEM. THE MOST WIDESPREAD MID LEVEL CLOUDS ARE NEAR THE INTERSTATE 75 CORRIDOR. IN FACT...SOME WEAK RETURNS ARE WORKING ACROSS THE SW PART OF THE CWA NEARER TO THE TN BORDER. NO MEASURABLE RAIN HAS BEEN OBSERVED SO FAR WITH THIS. IN THE VERY NEAR TERM WE HAVE OPTED TO JUST INCLUDE SPRINKLES ACROSS THE SOUTHERN COUNTIES FROM MCCREARY EAST INTO HARLAN COUNTY. THE ARRIVAL OF THE MID LEVEL CLOUDS HAS AT LEAST TEMPORARILY LED TO IMPROVED VIS IN THE FOG IN MOST AREAS PER RECENT OBSERVATIONS OTHER THAN KI35 AND KPBX AND SOME OF THE BIG SANDY REGION WHERE THE FOG HAS BEEN LOCALLY DENSE. THE MID CLOUDS MOVING OVERHEAD SHOULD LEAD TO IMPROVEMENTS THERE AS WELL OTHER THAN IN BREAKS OR HOLES IN THE CLOUDS THROUGH DAWN. BEHIND THE MID LEVEL DISTURBANCE TO WORK ACROSS THE REGION THIS MORNING...THE MID LEVEL MOISTURE NEAR 700 MB SHOULD ALSO DECREASE BUT THE LAYER BETWEEN 850 MB AND 750 MB SHOULD STILL REMAIN RATHER MOIST. SOME SHALLOW DIURNALLY DRIVEN CU WILL BE POSSIBLE IN THIS LAYER FROM MID DAY INTO THE AFTERNOON...AS DRIER AIR IS EXPECTED TO MOVE IN... ESPECIALLY ALOFT...BEHIND THE DISTURBANCE. 500 MB HEIGHTS ARE EXPECTED TO RISE AS HIGH PRESSURE ALOFT BUILDS INTO THE LOWER OH VALLEY FROM THE CENTRAL AND SOUTHERN PLAINS REGIONS. A SUBSIDENCE INVERSION BETWEEN 800 MB AND 700 MB SHOULD RESULT AND IS EXPECTED TO REMAIN THROUGH THE END OF THE SHORT TERM PERIOD. AT THE SFC...A LARGE AREA OF HIGH PRESSURE CURRENTLY CENTERED OVER ONTARIO WILL BUILD INTO THE OH VALLEY AND NORTHEASTERN STATES THROUGH EARLY THIS EVENING. THE HIGH IS EXPECTED TO REACH THE NEW ENGLAND COAST BY THE END OF THE PERIOD. FOG SHOULD DEVELOP TONIGHT...ESPECIALLY IN VALLEY LOCATIONS UNDER LIGHT WINDS AND MOSTLY CLEAR TO CLEAR SKIES. AN INVERTED SFC TROUGH IS EXPECTED TO DEVELOP NORTH INTO EASTERN KY LATE TONIGHT AND INTO THE DAY ON FRIDAY. THE INVERTED TROUGH SHOULD WEAKEN AND GRADUALLY SHIFT WEST BY THE END OF THE PERIOD. THIS INVERTED TROUGH SHOULD DRAW ENOUGH MOISTURE WEST ACROSS THE APPALACHIANS FOR SOME MOSTLY RATHER SHALLOW CU DEVELOPMENT BELOW THE SUBSIDENCE INVERSION ON FRI FROM MIDDAY INTO THE EVENING. SOME OF THIS COULD BECOME DEEP ENOUGH FOR A FEW SPRINKLES OR EVEN A STRAY SHOWER OR TWO NEAR THE VA BORDER. FOR NOW...WE HAVE CONTINUED WITH A DRY FORECAST AS MOS GUIDANCE GENERALLY HAS 10 PERCENT OR LOWER POPS. HOWEVER...SEVERAL OF THE 0Z MODELS DO HAVE SOME LIGHT PRECIPITATION NEAR THE VA BORDER ON FRI AFTERNOON. THE MODEL BLENDS ALSO HAVE SLIGHT CHANCE POPS IN THAT AREA AS WELL FOR FRI...SO THIS SCENARIO WILL NEED TO CONTINUE TO BE MONITORED. .LONG TERM...(FRIDAY NIGHT THROUGH WEDNESDAY) ISSUED AT 328 AM EDT THU SEP 18 2014 A SHORTWAVE AND INVERTED TROUGH OVER THE APPALACHIANS SHOULD BE TRANSITIONING EASTWARD AND OUT OF THE REGION BY 0Z SATURDAY. MORE ZONAL FLOW AND HIGH PRESSURE AT THE SURFACE WILL TAKE HOLD FOR THE DAY SATURDAY. MEANWHILE...THE LONGWAVE PATTERN IS PLANNED TO DEEPEN ACROSS SOUTH CENTRAL CANADA AND THE NORTH CENTRAL CONUS...EVENTUALLY MAKING ITS WAY EASTWARD INTO THE OHIO RIVER VALLEY SUNDAY AND MONDAY. THIS WILL RESULT IN A COLD FRONT TRAVERSING KY DURING THE DAY SUNDAY. THE FRONT SHOULD EVENTUALLY PASS THROUGH THE JKL FORECAST AREA...BUT MODELS ARE STILL NOT LOCKED IN ON SIMILAR TIMING. A MODEL BLEND WOULD SUGGEST SUNDAY AFTERNOON/EVENING...AND WILL CENTER THE HIGHEST POPS AT THAT TIME. AS WITH THE UNCERTAIN START TIMES...THE EXIT OF THIS FRONT IS ALSO STILL SOMEWHAT UNDETERMINED. WILL LEAN MORE TOWARDS A BLEND OF EXTENDED MODELS AT THIS TIME UNTIL BETTER COHERENCY TAKES PLACE IN LATER MODEL RUNS. SOUTHERLY WINDS JUST AHEAD OF THIS FRONTAL PASSAGE...AS WELL AS INCOMING CLOUD COVER...WILL KEEP TEMPS A LITTLE ABOVE SEASONAL FOR SATURDAY THROUGH SUNDAY NIGHT. KEPT WITH ONLY MENTIONING SLIGHT CHANCE THUNDER FOR DURING THE DAY SUNDAY. JUST NOT PICKING UP ON A LOT OF INSTABILITY ACROSS THE REGION...IN ADDITION TO THE FACT THAT THE FRONTAL BOUNDARY SHOULD BE WEAKENING/SHEARING OUT AS IT REACHES OUR AREA. 18Z SUNDAY SOUNDINGS SEEM TO SHOW THE BEST INSTABILITY POTENTIAL /THOUGH STILL MARGINAL/...BUT WINDS ARE NEARLY UNIDIRECTIONAL FROM THE WEST...SO DON/T EXPECT ANYTHING THAT DEVELOPS TO STAY SUSTAINED FOR ANY LONG PERIOD OF TIME. BEHIND THIS EXITING TROUGH WILL COME STRONG UPPER LEVEL RIDGING AND SURFACE SUBSIDENCE. THIS WILL KEEP MUCH OF THE CENTRAL CONUS DRY THROUGH THE REMAINDER OF THE EXTENDED /MONDAY FORWARD/. THE DEPTH OF THIS RIDGE WILL ALSO WORK TO PULL STRONG NORTHERLY/CANADIAN AIR IN THE LOW...MID...AND UPPER LEVELS ACROSS KENTUCKY. TEMPERATURES WILL BE COLDEST ON TUESDAY...WHEN SOME OF THE BEST/STRONGEST NORTHERLY AIR IS TAPPED INTO. BUT OVERALL...HIGHS SHOULD ONLY REACH THE UPPER 60S AND LOW 70S FOR THE REMAINDER OF THE EXTENDED. WITH STRONG RADIATIONAL COOLING EXPECTED OVERNIGHT UNDER MOSTLY CLEAR SKIES...EARLY MORNING LOWS WILL STAY IN THE UPPER 40S/LOW 50S. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING) ISSUED AT 755 AM EDT THU SEP 18 2014 A WEAKENING DISTURBANCE INTO THE LOWER OH VALLEY REGION ATTM. THIS FEATURE HAS BROUGHT SOME MID LEVEL MOISTURE AND MID LEVEL CLOUDS AND EVEN SOME SPRINKLES AND STRAY LIGHT SHOWERS TO THE REGION. HOWEVER...THE STRAY LIGHT SHOWERS AND SPRINKLES ARE DIMINISHING AND WHAT IS LEFT OF THESE WILL NOT IMPACT THE TAF SITES. OTHERWISE... THE FOG THAT DEVELOPED BEFORE THESE BANDS OF CLOUDS MOVED ACROSS THE REGION HAS LIFTED ONTO THE RIDGES IN SOUTHEASTERN KY. THE FOG WILL INITIALLY BE DENSE AT SJS...BUT SHOULD GRADUALLY LIFT WITH VFR BY 1430Z. SOME VFR OR MVFR FOG IS ANTICIPATED AT THE REMAINING TAF SITES INITIALLY WITH ALL LOCATIONS IMPROVING INTO VFR AROUND OR SHORTLY AFTER 14Z. ANY CU THAT DEVELOPS AND REMAINING MID LEVEL CLOUDS WILL REMAIN IN THE VFR RANGE THROUGH AROUND 22Z WHEN THEY DISSIPATE. FOG... REDUCING VIS DOWN INTO THE MVFR RANGE...OR POSSIBLY IFR RANGE WILL AGAIN BE POSSIBLE DURING THE LAST 6 HOURS OF THE PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...JP LONG TERM...JMW AVIATION...JP

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