Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 130128 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 928 PM EDT SAT JUL 12 2014 .UPDATE... ISSUED AT 928 PM EDT SAT JUL 12 2014 WITH WINDS DECOUPLING IN THE VALLEYS...TEMPS HAVE DROPPED AND DEW POINTS HAVE JUMPED. HAVE UPDATED GRIDS TO ACCOUNT FOR THE LATEST OBS. THE FORECAST FOR OVERNIGHT REMAINS UNCHANGED. UPDATE ISSUED AT 614 PM EDT SAT JUL 12 2014 A SIGNIFICANT AMOUNT OF CIRRUS HAS MOVED INTO THE REGION...BUT IT WAS GRADUALLY DISSIPATING. INCREASED SKY COVER FOR EARLY THIS EVENING...BUT STAYED WITH A TREND TOWARD THE LOWER VALUES OF THE PREVIOUS FORECAST FOR LATE TONIGHT. DRY SURFACE AIR AND WARM AIR ADVECTION TONIGHT WOULD FAVOR SOME RIDGE/VALLEY TEMPERATURE DIFFERENCES...AND HAVE LOWERED VALLEY MINS JUST A BIT FOR TONIGHT. WITHOUT OVERCAST SKIES OR SIGNIFICANT WIND...CLIMATOLOGY STRONGLY FAVORS AT LEAST SOME FOG IN THE DEEPER VALLEYS AT THIS TIME OF YEAR. SO...DESPITE THE DRY AIR...HAVE ADDED SOME PATCHY FOG IN VALLEYS FOR LATE TONIGHT...BUT PREVIOUS THINKING OF LESS SUBSTANTIAL FOG THAN IN RECENT NIGHTS SHOULD STILL PLAY OUT. && .SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT) ISSUED AT 315 PM EDT SAT JUL 12 2014 ISOLATED CONVECTION MAINLY TIED TO TERRAIN IS EXPECTED TO REMAIN TO OUR SOUTH AND SOUTHEAST OVER SW VA AND THE HIGHER TERRAIN OF TN AND NC FOR THE REMAINDER OF THIS AFTERNOON. THE AREA OF SHOWERS AND THUNDERSTORMS OVER WESTERN INDIANA AND WESTERN KY IS AHEAD OF A NEARLY STATIONARY WARM FRONTAL BOUNDARY THAT REPRESENTS THE LEADING EDGE OF 70 PLUS DEW POINT TEMPERATURES OVER IL AND MO. SATELLITE...RADAR AND LIGHTNING TRENDS ALL SHOW CONTINUING WEAKENING OF CONVECTION OVER INDIANA...BUT THERE HAS BEEN SOME DEVELOPMENT INTO WESTERN KY. THE SHORT RANGE RAP AND HRRR CONTINUE TO SHOW OVERALL DECAY OF CONVECTION TO OUR WEST...AND ONLY IMPACT IN OUR AREA WILL BE SOME INCREASE IN HIGH LEVEL CLOUDS. WITH VERY DRY LOW LEVEL AIR IN PLACE IN EASTERN KY THIS AFTERNOON...NOTE DEW POINT AS LOW AS 48 AT QUICKSAND MESONET...THERE WILL BE EVEN LESS FOG TONIGHT AS THERE WAS LAST NIGHT. GUIDANCE NOT HANDLING THE DRY AIR VERY WELL...AND EXPECT THERE TO BE ABOUT A 5 DEGREE RIDGE VALLEY TEMPERATURE SPLIT FOR TONIGHT. ON SUNDAY INSTABILITY WILL INCREASE AHEAD OF AN APPROACHING COLD FRONT WITH MUCAPE IN EXCESS OF 4000 J/KG DEVELOPING IN A CORRIDOR NORTH OF THE OH RIVER ACROSS SOUTHERN IN AND OH. BEST SHEAR WILL ALSO BE NORTH OF THE OH RIVER SUNDAY AFTERNOON AND CURRENT THINKING IS THAT THUNDERSTORMS WILL DEVELOP ACROSS OH AND INDIANA AND THEN PROGRESS INTO NORTHERN PARTS OF THE FORECAST AREA LATE SUNDAY AFTERNOON OR SUNDAY NIGHT. AT THE SAME TIME SOME ISOLATED TO SCATTERED CONVECTION MAY DEVELOP OVER THE SOUTHEAST MOUNTAINS SUNDAY AFTERNOON. THIS WOULD ALSO BE IN A CORRIDOR OF SLIGHTLY GREATER INSTABILITY AND ALSO PARTIALLY TIED TO THE HIGHER TERRAIN. THE MODELS HAVE BEEN CONSISTENT AT HINTING AT THIS POSSIBILITY IN THE SE FORECAST AREA. CONSIDERING ALL THIS WILL BRING CHANCE PROBABILITY OF SHOWERS AND THUNDERSTORMS TO THE SOUTHEAST AND NORTHERN PARTS OF THE FORECAST AREA FIRST ON SUNDAY...WITH THE CENTRAL AND SOUTHWEST PARTS OF THE FORECAST AREA THE LAST TO SEE THE RAIN CHANCES. THE CONVECTION THAT DEVELOPS TO OUR NORTH ON SUNDAY HAS SEVERE POTENTIAL...BUT AS IT MOVES INTO OUR AREA SUNDAY NIGHT AWAY FROM BEST SUPPORT...THE SEVERE THREAT WILL DECREASE. THE DAY 2 SEVERE WEATHER OUTLOOK WITH ONLY OUR FAR NW COUNTIES HAVING A SLIGHT RISK OF SEVERE WEATHER THROUGH 12Z MONDAY CONTINUES TO LOOK GOOD. WITH PW INCREASING THROUGH SUNDAY NIGHT TO 1.7 TO POSSIBLY GREATER THAN 2 INCHES SOME HEAVY RAINERS ARE DEFINITELY A POSSIBILITY SUNDAY NIGHT. MUCH OF THE AREA HAS BEEN PLACED IN THE DAY 2 EXCESSIVE RAINFALL OUTLOOK VALID 00Z MONDAY TO 00Z TUESDAY. FLASH FLOOD GUIDANCE IS FAIRLY HIGH HOWEVER...AND PART OF THE AREA IS CURRENTLY IN D1 DROUGHT. INITIALLY... AT LEAST FOR SUNDAY NIGHT...WHICH IS THE FIRST HALF OF THIS OUTLOOK PERIOD THE FLASH FLOOD THREAT LOOKS BE ISOLATED AT WORST. .LONG TERM...(MONDAY THROUGH SATURDAY) ISSUED AT 315 PM EDT SAT JUL 12 2014 THE GFS IS SHOWING SOME DECENT CONTINUITY THROUGH THE LAST FEW CYCLES BUT STILL APPEARS OUTSIDE THE RANGE OF OTHER SOLUTIONS AND TOO PROGRESSIVE...ESPECIALLY CONSIDERING THE EXPECTED AMPLITUDE OF THE MID AND UPPER LEVEL PATTERNS. THE ECMWF...WHICH HAS BEEN MORE CONSISTENT IS ADVERTISING A SLOWER SYSTEM THAT PUNCHES FURTHER SOUTH THAN OTHER MODELS AND IS ON THE SLOWER SIDE OF THE ENVELOPE OF SOLUTIONS THROUGH THE MID TERM. JUST THE SAME MODELS ROUGHLY AGREE ON THE OVERALL SCENARIO OF THE LARGE SCALE PATTERN. THE MAIN...AND MOST SIGNIFICANT DIFFERENCES CROP UP RESOLVING SURFACE FEATURES AND THE TIMING OF SFC SYSTEMS THROUGH OUR AREA. ATTM TENDENCY IS TO LEAN TOWARDS THE ECMWF SOLUTION THROUGH THE MID RANGE AFTER USING A CONSENSUS SOLUTION TO INITIALIZE THE EXTENDED PORTION OF THE FORECAST PACKAGE. WILL STICK TO A BLENDED APPROACH FOR THE END OF THE FORECAST WINDOW AS ADDITIONAL ENERGY EMERGES FROM THE PACIFIC NW/CANADA CAUSING THE PATTERN TO BECOME LESS AMPLIFIED...BUT ALSO ALLOWING FOR THE MEAN STORM TRACK TO RETURN NORTHWARD CLOSER TO OUR NECK OF THE WOODS. HEIGHTS FALL DROP STEADILY THROUGH THE FIRST HALF OF THE PERIOD AS A SPLITTING UPPER LEVEL LOW DROPS A SIGNIFICANT PORTION OF ITS ENERGY INTO THE THE UPPER MIDWEST AND GREAT LAKES...RESULTING IN A LARGE DEEP TROUGH ACROSS THE ENTIRE EASTERN CONUS BY MID WEEK. SURFACE FRONTAL ZONE WILL DROP SOUTHWARD ALONG THE OHIO RIVER BY LATE SUNDAY OR SUNDAY NIGHT. A SECOND STRONGER...FASTER FRONTAL BOUNDARY WILL FOLLOW QUICKLY BEHIND THE FIRST SLIDING THROUGH OUR AREA AS SOON AS MONDAY NIGHT...OR AS LATE AS TUESDAY AFTERNOON DEPENDING ON WHICH MODEL YOU LOOK AT. IT STILL SEEMS LIKE THE GFS IS HAVING TROUBLE RESOLVING THE TIMING OR PASSAGE OF THESE TWO FRONTAL BOUNDARIES... WITH A TENDENCY TO MERGE EACH DISTINCT BOUNDARY INTO A SINGLE FINAL SYSTEM THAT MOVES THROUGH EASTERN KENTUCKY TOO QUICKLY. WE ARE STILL LOOKING AT THE POTENTIAL FOR SOME SEVERE WEATHER THOUGH THE TIME OF DAY AND EXACT AMOUNT OF SUNLIGHT WILL BE SOMETHING THAT WILL NEED TO BE FACTORED IN. AS IS TYPICAL...THE NAM IS CONSIDERABLY MORE UNSTABLE IN THE BOUNDARY LAYER BECAUSE OF ITS WET BIAS. THE NAM IS ALSO SHOWING HIGHER BULK SHEAR VALUES THROUGH THE EARLY MONDAY MORNING TO MONDAY AFTERNOON TIME FRAME. PWATS AND LIFT THROUGH THE COLUMN ARE MUCH MORE IMPRESSIVE AS WELL WHEN COMPARED TO THE GFS. EXPECT THE TRUTH WILL LIE SOMEWHERE IN THE MIDDLE THOUGH THAT MAY BE A BAD ASSUMPTION GIVEN THE GFS MIGHT BE HAVING TROUBLE DISTINGUISHING SURFACE AND BOUNDARY LAYER DETAILS. FREEZING LEVELS REMAIN HIGH. SO WHILE SOME HEAVY RAIN CAN NOT BE RULED OUT...STORM MOTION IS HIGH ENOUGH THAT HYDRO PROBLEMS SHOULD NOT BECOME TOO MUCH OF A PROBLEM...AT LEAST BASED ON CURRENT GUIDANCE. BIGGEST THREAT FOR SEVERE WEATHER WILL GENERALLY LIE ACROSS OUR BLUE GRASS COUNTIES SUNDAY...BUT THEN EXPAND SOUTHEASTWARD TO ENCOMPASS OUR ENTIRE FORECAST AREA BY MONDAY. WE ARE STILL LOOKING AT UNSEASONABLE COLD WEATHER FOR THE PEAK OF SUMMER HEATING THROUGH THE MIDDLE OF UPCOMING WEEK. ECMWF H850 TEMPS DROP TO AROUND 8C AND THE GFS HAS TRENDED TOWARDS THE ECMWF. ECMWF MOS GUIDANCE IS QUITE COOL WITH AFTERNOON HIGHS IN THE LOWER TO MID 70S AND LOWS SOLIDLY IN THE 50S FROM TUESDAY THROUGH FRIDAY. WHILE THERE IS SOME MODERATION TOWARDS THE END OF THE WEEK...THERE IS A GOOD POTENTIAL FOR SOME RECORD COLD MORNING LOWS AND EVEN A FEW RECORD LOW MAXES. GFS MOS IS CONSIDERABLY WARMER BUT HAS SHOWN SIGNS OF COOLING. PAST EXPERIENCE HAS TAUGHT THAT A BLEND OF GUIDANCE MAKES A BEST FIRST GUESS...AFTER A TWEAK TOWARDS THE TYPICALLY MORE ACCURATE ECMWF MOS. ADDITIONAL ENERGY MOVING OUT OF THE NORTHWEST AND INTO THE BASE OF THE BY THEN LIFTING EASTERN CONUS TROUGH WILL BRING A THREAT OF RAIN BACK INTO THE FORECAST AREA AT THE END OF THE WEEK AND INTO THE WEEKEND. && .AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING) ISSUED AT 723 PM EDT SAT JUL 12 2014 PREDOMINANTLY VFR WITH LIGHT WINDS IS EXPECTED DURING THE PERIOD. AN EXCEPTION WILL BE LOCALIZED FOG IN DEEP VALLEYS LATE TONIGHT AND EARLY SUNDAY. THERE COULD ALSO BE A FEW SHOWERS AND THUNDERSTORMS POPPING UP DURING THE DAY ON SUNDAY...WITH LOCALIZED RESTRICTIONS TO CIGS/VSBY. THE PROBABILITY OF ANY GIVEN TAF SITE GETTING HIT IS TOO LOW TO WARRANT MENTIONING IT IN A TAF AT THIS POINT. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...HAL SHORT TERM...SBH LONG TERM...RAY AVIATION...HAL

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