Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 171530 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 1030 AM EST WED DEC 17 2014 .UPDATE...
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ISSUED AT 1030 AM EST WED DEC 17 2014 14Z SFC ANALYSIS SHOWS CYCLONIC LOW LEVEL FLOW OVER EASTERN KENTUCKY SUBSIDING IN RESPONSE TO HIGH PRESSURE MOVING INTO THE WESTERN TENNESSEE VALLEY. HOWEVER...PLENTY OF MOISTURE REMAINS IN PLACE IN THE LOWEST PARTS OF THE ATMOSPHERE ACROSS THE AREA. THIS IS KEEPING LOW CLOUDS AND LIGHT PCPN AROUND EASTERN KENTUCKY...PARTICULARLY NORTHEAST OF JKL. FOR THE MOST PART THE PCPN TAKES THE FORM OF DRIZZLE...BUT SOME LIGHT RAIN IS POSSIBLE OVER THE NORTHEAST WHILE SOME FLURRIES HAVE BEEN NOTED THROUGH THE NORTHWESTERN PARTS OF THE AREA. ALSO...IN THE HIGHER TERRAIN OF THE FAR EAST...TEMPERATURES HAVE FALLEN BELOW OR RIGHT TO FREEZING...BLACK MOUNTAIN AT 29 AND DORTON AT 32...RESULTING IN A POTENTIAL FOR FREEZING DRIZZLE AND SLICK SPOTS IN THESE LOCATIONS. AN SPS REMAINS IN EFFECT FOR THESE CONCERNS THROUGH NOON. OTHERWISE...THE FORECAST IS ON TRACK WITH THE PCPN WANING IN THE AFTERNOON AND CLOUDS SLOWLY TRYING TO BRIEFLY BREAK UP LATE IN THE DAY. HAVE MADE SOME MINOR ADJUSTMENTS TO HOURLY TEMPS AND DEWPOINTS BASED ON THE LATEST OBS...TRENDS...AND BCCONSSHORT GUIDANCE. THESE HAVE BEEN SENT TO THE NDFD AND WEB SERVERS WITH AN UPDATE TO THE ZONES AND HWO TO FOLLOW ONCE THE THREAT FOR FREEZING PCPN HAS PASSED. UPDATE ISSUED AT 722 AM EST WED DEC 17 2014 OVER THE LAST FEW HOURS...LATEST IR IMAGERY HAS SHOWN SOME COLDER CLOUD TOPS ADVECTING EASTWARD INTO THE REGION. THIS...IN ADDITION TO MORNING TEMPERATURES IN THE LOW TO MID 30S ACROSS PORTIONS OF EASTERN KY...HAS LED TO SOME ISOLATED FLURRY REPORTS. EXPECT THESE COLDER CLOUDS CONTINUE MOVING ACROSS EASTERN KY. THE COMBINATION OF ONGOING DRIZZLE THIS MORNING...LOWERING TEMPS ALOFT...AND LOW TO MID 30S SURFACE TEMPS EXPECTED TO STICK AROUND FOR SEVERAL HOURS LONGER...WARRANTED THE BELIEF THAT A GOOD PORTION OF THE AREA COULD SEE SOME FLURRY POTENTIAL...EVEN IF ONLY A SLIGHT CHANCE. WENT AHEAD AND COMBINED ISOLATED FLURRY POTENTIAL WITH THE ONGOING AREAS OF DRIZZLE IN THE WEATHER GRIDS. THIS WILL HAVE THE FLURRIES ENDING ALONG WITH THE DRIZZLE AS DRY AIR FINALLY MIXES DOWN TO THE SURFACE BY LATE MORNING/EARLY AFTERNOON.
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&& .SHORT TERM...(TODAY THROUGH THURSDAY) ISSUED AT 426 AM EST WED DEC 17 2014 A WEAK BOUNDARY PASSING THROUGH THE REGION OVERNIGHT HAS PROMPTED A SLIGHT INCREASE IN MOISTURE...WHICH HAS RESULTED IN LIGHT RAIN SHOWERS ACROSS A GOOD PORTION OF THE NORTHERN HALF OF THE CWA. AS THE BOUNDARY /WHICH IS IN THE FORM OF A WEAK COLD FRONT CONNECTED TO LOW PRESSURE CURRENTLY TRACKING ACROSS THE LOWER GREAT LAKES/ CONTINUES EASTWARD OUT OF KY...EXPECT SHOWERS TO COME TO AN END FROM W TO E THROUGH 11Z. FORECAST SOUNDINGS ARE STILL SUPPORTING DRIZZLE HANGING AROUND MUCH OF THE AREA THROUGH MID MORNING TO EARLY AFTERNOON AS A STRONG SUBSIDENCE INVERSION KEEPS LOW LEVEL MOISTURE IN PLACE. BETWEEN 15 AND 18Z...DRY AIR WILL FINALLY BEGIN TO MIX DOWN...AND LOW CLOUDS WILL BREAK. UNFORTUNATELY...HIGH CLOUDS WILL BE BUILDING IN AROUND THE SAME TIME AS THE NEXT SYSTEM APPROACHES THE REGION. WENT ABOVE GUIDANCE ON CLOUD COVER...KEEPING BKN CLOUDS ACROSS MUCH OF THE CWA AS THIS TRANSITION OCCURS. CONCERNING THE APPROACHING SYSTEM...A SHORTWAVE IS EXPECTED TO DEVELOP ALONG THE LEEWARD SIDE OF AN UPPER LEVEL TROUGH WHICH WILL BE SITTING ALONG THE PACIFIC COAST TODAY. AS THIS SHORTWAVE RACES OUT AHEAD OF THE TROUGH...IT WILL CREATE A DISTURBANCE WHICH WILL BEGIN PULLING MOISTURE IN FROM THE GULF COAST AS IT REACHES THE MISSISSIPPI RIVER VALLEY WEDNESDAY NIGHT/THURSDAY MORNING. ALL MODELS ARE SHOWING PRECIP REACHING WESTERN AND SOUTH CENTRAL KY BETWEEN 6 AND 12Z THURSDAY. HOWEVER...DIGGING A LITTLE DEEPER...THIS SYSTEM IS NOT ALL THAT IS APPEARS. FIRST OFF...KY WILL BE UNDER THE INFLUENCE OF A STRONG HIGH PRESSURE SYSTEM AT THE SURFACE. FURTHER MORE...FORECAST SOUNDINGS ARE SHOWING A STRONG LAYER OF DRY AIR NEAR THE SURFACE IN RESPONSE TO THE SURFACE HIGH. WHAT MOISTURE ACCOMPANIES THIS SHORTWAVE WILL BE SHALLOW...AND WILL HAVE TO FALL THROUGH A FAIRLY SUBSTANTIAL AMOUNT OF LOW LEVEL DRY AIR. AFTER COLLABORATION WITH SURROUNDING OFFICES...DECIDED TO SUBSTANTIALLY DROP POPS FROM GUIDANCE. SINCE MODELS WERE PLACING THE BEST POTENTIAL FOR PRECIP ACROSS OUR SW COUNTIES IN THE CWA...DID KEEP SLIGHT CHANCES HERE. HOWEVER FOR EVERYWHERE ELSE...WILL MORE THAN LIKELY SEE A SPRINKLE/FLURRY EVENT BASED ON THE GFS AND NAM SOUNDINGS. THE SHORTWAVE WILL QUICKLY PHASE OUT ACROSS KY...WITH ANY LINGERING PRECIP EXPECTED TO END THURSDAY EVENING...THOUGH SOME MID LEVEL CLOUDS WILL LIKELY STICK AROUND. FAIRLY ZONAL FLOW AND ABUNDANT CLOUD COVER ACROSS THE REGION WILL WORK TO KEEP FAIRLY STEADY TEMPS IN THE FORECAST FOR THE NEXT 36 TO 48 HOURS. HIGHS WILL BE IN THE UPPER 30S AND LOW 40S...WITH A FAIRLY SMALL DIURNAL DROP TO THE UPPER 20S TO AROUND 30 DURING THE OVERNIGHT. .LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY) ISSUED AT 441 AM EST WED DEC 17 2014 THE MODELS ARE IN GOOD AGREEMENT WITH A PROGRESSIVE LONG WAVE PATTERN TO HOLD ON THROUGH THE END OF THE WEEK...FOLLOWED BY STRONGER AMPLIFICATION INTO EARLY NEXT WEEK. SMALL SCALE FEATURES WITHIN THE LONG WAVE PATTERN HAVE COME INTO BETTER AGREEMENT THROUGH THE WEEKEND...WITH MUCH LESS AGREEMENT INTO EARLY NEXT WEEK. THE BLENDED GUIDANCE OFFERED A GOOD COMPROMISE AND STUCK FAIRLY CLOSE TO IT. A DAMPENING SHORT WAVE TROUGH WILL BE EXITING ACROSS THE OHIO VALLEY EARLY IN THE PERIOD...WITH A FEW FLURRIES/SPRINKLES LINGERING IN THE NORTHEAST KENTUCKY EARLY THURSDAY EVENING. MEANWHILE...THE MAIN SOUTHERN STREAM TROUGH WILL BE MOVING ALONG THE GULF COAST AND THEN EVENTUALLY SWING MORE TOWARDS THE SOUTHERN APPALACHIANS THROUGH THE END OF THE WEEKEND. THE ASSOCIATED SURFACE LOW TRACK HAS CONTINUED FURTHER SOUTH. THERE HAS ALSO BEEN A WEAKER TREND WITH THIS SYSTEM. THE ECMWF AND GFS CONTINUE TO STICK TO THEIR DIFFERING THERMAL PROFILES...WITH THE ECMWF COLDER AND SUPPORTIVE OF AT LEAST A LITTLE SNOWFALL UP NORTH...WHILE THE GFS MAINTAINS ITS MAINLY ALL RAIN SOLUTION. AS SUCH...WILL KEEP A GENERAL BLEND OF BOTH SOLUTIONS GOING...ALLOWING FOR A LITTLE SNOW GENERALLY NEAR AND NORTH OF THE MOUNTAIN PARKWAY. AFTER A DRY FRIDAY...PRECIPITATION WILL MOVE INTO EASTERN KENTUCKY LATE FRIDAY NIGHT INTO SATURDAY FROM SOUTHWEST TO NORTHEAST...BEFORE DIMINISHING INTO SATURDAY NIGHT. SUNDAY INTO MONDAY LOOK DRY AS HIGH PRESSURE AT THE SURFACE TAKES HOLD. DEEP TROUGHING WILL THEN TAKE SHAPE ACROSS THE CENTRAL CONUS. THERE IS DISAGREEMENT IN THE EVOLUTION AND TIMING OF A LIKELY STRONGER SURFACE SYSTEM TO CONTEND WITH FROM LATE MONDAY NIGHT ONWARD. STUCK CLOSE TO THE BLENDED GUIDANCE GIVEN THE LOWER CONFIDENCE THIS FAR OUT...WITH CHANCES OF SHOWERS RETURNING TO THE FORECAST FOR MONDAY NIGHT AND TUESDAY. TEMPERATURES WILL AVERAGE BELOW NORMAL THROUGH THE WEEKEND...BEFORE MODIFYING TO NEAR NORMAL THROUGH EARLY NEXT WEEK. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING) ISSUED AT 739 AM EST WED DEC 17 2014 LOW LEVEL MOISTURE REMAINS TRAPPED BY A STRONG SUBSIDENCE INVERSION AS WE HEAD INTO THE MORNING HOURS ACROSS EASTERN KY. AREAS OF DRIZZLE AND EVEN SOME ISOLATED FLURRIES ARE POSSIBLE TO START OFF THE TAF PERIOD. WHILE MOST TAF SITES CONTINUE TO FLUCTUATE BETWEEN IFR AND MVFR CIGS...KJKL HAS DROPPED TO AROUND 300FT DUE TO SOME HEAVIER PRECIP THAT IS CURRENTLY MOVING ACROSS THE TAF SITE. IN GENERAL...EXPECT DRY AIR TO FINALLY MAKE IT TO THE SURFACE DURING THE LATE MORNING/EARLY AFTERNOON HOURS...ALLOWING PRECIP TO END...BUT BKN MVFR CLOUDS TO CONTINUE. BY THIS EVENING...MODELS ARE SHOWING THE LOW CLOUDS FINALLY SCATTERING OUT. ANOTHER DISTURBANCE WILL THEN MOVE INTO THE REGION OVERNIGHT TONIGHT...BRINGING THE POTENTIAL FOR SOME LIGHT SNOW LATE TONIGHT/EARLY TOMORROW MORNING FOR KSME AND KLOZ. HOWEVER...LOW LEVEL DRY AIR WILL MAKE IT HARD FOR THE PRECIP TO ACTUALLY REACH THE SURFACE. THEREFORE CONFIDENCE IS TOO LOW TO MENTION IN TAFS AT THIS TIME. FINALLY...STRONG WINDS ALOFT MAY BE OF CONCERN OVER THE NEXT 24 HOURS. AN UPPER LEVEL JET HAS SET UP ACROSS KY...AND WILL BRING CONTINUED STRONG WESTERLY FLOW IN THE MID AND UPPER LEVELS. THE STRONG SUBSIDENCE INVERSION IN PLACE SHOULD KEEP WINDS LIGHT WITHIN THE FIRST FEW THOUSAND FEET AGL. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...JMW LONG TERM...GEOGERIAN AVIATION...JMW

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