Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 210749 AFDJKL AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE JACKSON KY 349 AM EDT SUN SEP 21 2014 .UPDATE... ISSUED AT 225 AM EDT SUN SEP 21 2014 HOURLY GRIDS HAVE BEEN FRESHENED UP BASED ON THE LATEST OBSERVATIONS. THIS LED TO A BIT MORE FOG IN THE GRIDS...ESPECIALLY IN SOME OF THE WESTERN BROAD VALLEY LOCATIONS AND OPTED TO GO WITH PATCHY DENSE FOG FOR THE DEEPER SOUTHEASTERN VALLEYS BASED ON OB FROM KI35. HOURLY TEMPS WERE RUNNING AT OR BELOW MIN T FORECAST FOR SOME OF THE VALLEY LOCATIONS SO MIN T WAS LOWERED A COUPLE OF DEGREES IN A FEW SPOTS TO ALLOW FOR A COUPLE MORE DEGREES OF DROP BEFORE CLOUDS INCREASE ALONG WITH THE PRESSURE GRADIENT AS A COLD FRONT APPROACHES. UPDATE ISSUED AT 1023 PM EDT SAT SEP 20 2014 THE FORECAST IS STILL ON TRACK SO FAR TONIGHT. THE LATEST OBS WERE INGESTED INTO THE FORECAST TO ESTABLISH NEW TRENDS AND FRESHEN UP THE DATA A BIT. WE STILL LOOK TO BE ON TRACK TO HAVE SOME PATCHY VALLEY OVERNIGHT WITH INCREASING CLOUDINESS LATE TONIGHT AND ISOLATED RAIN SHOWERS MOVING INTO OUR NORTHWESTERN COUNTIES AROUND 11Z TOMORROW. UPDATE ISSUED AT 728 PM EDT SAT SEP 20 2014 QUIET FORECAST ON TAP FOR THE REST OF THE NIGHT. SKIES WILL BE MOSTLY CLEAR FOR THE NEXT SEVERAL HOURS AS HIGH PRESSURE SLOWLY MOVES OFF TO THE EAST. BY LATE TONIGHT SCATTERED TO BROKEN LOW LEVEL CLOUD WILL BEGIN ROLLING INTO THE AREA AS A COLD FRONT APPROACHES FROM THE NORTHWEST. ISOLATED RAIN SHOWERS ARE THEN EXPECTED TO BEGIN MOVING INTO OUR NORTHWESTERN COUNTIES AROUND 12Z TOMORROW. ASIDE FROM UPDATING THE FORECAST GRIDS WITH THE LATEST OBS DATA...NO CHANGES WERE MADE TO THE FORECAST. && .SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT) ISSUED AT 311 PM EDT SAT SEP 20 2014 HIGH PRESSURE CONTINUES TO HOLD OVER THE EASTERN US THIS AFTERNOON...PROVIDING A DRY AND MILD START TO THE WEEKEND. HOWEVER...A POTENT SHORTWAVE TROUGH IS ALREADY DROPPING SOUTH INTO THE WESTERN GREAT LAKES/NORTHERN PLAINS. MODELS ARE IN FAIRLY GOOD AGREEMENT ON THE FORECAST THROUGH THE REMAINDER OF THE WEEKEND...PROVIDING DECENT FORECAST CONFIDENCE. THE SHORTWAVE TROUGH WILL CONTINUE TO DIVE SOUTHWARD TONIGHT THROUGH SUNDAY. THIS WILL PUSH A SURFACE COLD FRONT SOUTHWARD INTO THE OHIO RIVER VALLEY LATE TONIGHT. DECENT CONVERGENCE AND SOME UPPER LEVEL SUPPORT WILL PRODUCE SHOWERS AND A FEW THUNDERSTORMS AS THIS BOUNDARY SHIFTS SOUTH TONIGHT. INSTABILITY MAY WANE LATE TONIGHT...WITH LIMITED THUNDER POTENTIAL. HOWEVER...THE MAIN FRONT IS EXPECTED TO CROSS THE AREA DURING THE DAY TOMORROW...WITH INSTABILITY INCREASING ALONG AND JUST AHEAD OF THE BOUNDARY. THIS WILL WARRANT INCREASING COVERAGE THROUGH THE DAY AS THE FRONT SAGS SOUTHEASTWARD. THE FRONT WILL BE ON THE EXIT BY EARLY SUNDAY EVENING...WITH SUBSTANTIALLY DRIER AIR ADVECTING INTO THE AREA FROM EARLY TO LATE EVENING. IF ENOUGH INSTABILITY CAN DEVELOP SUNDAY AFTERNOON...WE COULD SEE A MARGINAL WIND THREAT DEVELOP WITH A FEW STORMS. HOWEVER...THIS REMAINS VERY UNCERTAIN AT THIS TIME. STAYED ABOVE GUIDANCE FOR LOWS TONIGHT GIVEN THE INCREASING WINDS AND MOISTURE AHEAD OF THE APPROACHING FRONT. STAYED FAIRLY CLOSE TO GUIDANCE FOR HIGHS TOMORROW AS CLOUDS AND SHOWERS MAY KEEP TEMPERATURES FROM GETTING ALL THAT WARM TOMORROW. SHOULD SEE A MUCH COLDER NIGHT SUNDAY NIGHT WITH THE COLD ADVECTION TAKING PLACE THROUGH THE NIGHT. WHILE SOME CLEARING MAY BE POSSIBLE...CLOUDS MAY FILL BACK IN OVERNIGHT AS A SECONDARY TROUGH DROPS SOUTH ACROSS EASTERN KENTUCKY. THUS...THIS MAY LIMIT FOG POTENTIAL SUNDAY NIGHT. .LONG TERM...(MONDAY NIGHT THROUGH SATURDAY) ISSUED AT 348 AM EDT SUN SEP 21 2014 A STRONG UPPER LEVEL RIDGE WILL MOVE FROM THE CENTRAL CONUS AT 0Z TUESDAY...TO THE MISSISSIPPI RIVER VALLEY BY 12Z. MEANWHILE...SURFACE HIGH PRESSURE WILL ALSO REMAIN STRONG OVER THE REGION...WITH WINDS BOTH AT THE SURFACE AND ALOFT PULLING DRY AND COLDER AIR IN FROM CANADA. SOME OF THE STRONGEST WINDS ALOFT WILL BE MOVING OFF TO OUR EAST WITH THE DEPARTING UPPER LEVEL TROUGH...BUT COLD AIR WILL LINGER THROUGH THE DAY TUESDAY. MORNING LOWS WILL ONLY BE IN THE LOW TO MID 40S...WITH AFTERNOON HIGHS TOPPING OUT AROUND OR JUST ABOVE THE 70 DEGREE MARK. OVER THE COURSE OF THE EXTENDED PERIOD...THE SURFACE HIGH WILL SHIFT SLIGHTLY TO OUR NE...BUT THE UPPER LEVEL RIDGE WILL REMAIN BLOCKED OVER THE REGION. AS SUCH...DRY AIR WILL PERSIST ACROSS MUCH OF THE OHIO RIVER VALLEY...THOUGH THE LOSS OF STRONGEST NRLY WIND FLOW AT BOTH THE SURFACE AND ALOFT WILL LEAD TO AIRMASS MODIFICATION AND RISING TEMPERATURES THROUGHOUT THE EXTENDED. TEMPS WILL REACH THE 80 DEGREE MARK IN SOME LOCATIONS ONCE MORE BY SATURDAY. THE LATEST ECMWF MODEL IS POINTING AT A WEAK LOW DEVELOPING NEAR THE REGION LATE IN THE PERIOD...NAMELY SATURDAY AND SUNDAY...ALLOWING MOISTURE FLOW AND PRECIP CHANCES TO MOVE INTO PORTIONS OF THE CWA. WHILE A COUPLE OF OUR NEIGHBORING OFFICES WERE ON BOARD WITH INCLUDING SLIGHT CHANCE POPS...THE UNCERTAINTY FAVORED LEAVING THEM OUT AT THE JKL CWA AT THIS TIME. SO FAR...THE MODEL AGREEMENT PAST THE MID TERM IS QUITE LOW. THE ECMWF SEEMS TO BE THE OUTLIER WITH THIS PRECIP...AND VERY LOW QPF AT THAT. MORE THAN LIKELY...THE SUPER BLEND IS BEING INFLUENCED BY THIS LATEST ECMWF RUN...WHICH LED TO THE MENTION OF A FEW 15 POPS IN THE SATURDAY NIGHT FORECAST. MEANWHILE...THE GFS SHOWS NO SIGN OF THIS LOW NEAR THE REGION /IT HAS IT DEVELOPING MUCH FARTHER S AND MUCH WEAKER/ OR ANY PRECIP MOVING INTO KENTUCKY. GIVEN THE UNCERTAINTY AT THIS POINT...LOWERED ANY 15 POPS FOR SATURDAY NIGHT BACK DOWN TO 14. WILL WAIT UNTIL MODELS COME INTO BETTER AGREEMENT OR SHOW MORE CONSISTENCY BETWEEN RUNS BEFORE DECIDING TO INCLUDE POPS IN THE FORECAST PACKAGE. && .AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT) ISSUED AT 145 AM EDT SUN SEP 21 2014 OUTSIDE OF PATCHY FOG...AFFECTING LOZ AND SME WITH MAINLY MVFR FOG AND SOME IFR OR LOWER FOG IN SOME OF THE DEEPER VALLEY LOCATIONS... MAINLY VFR SHOULD PREVAIL THROUGH AROUND 14Z. A COLD FRONT WILL DROP SOUTH INTO THE AREA AROUND SUNRISE WITH CLOUDS AND PRECIPITATION CHANCES ON THE INCREASE. AT THIS TIME...IT APPEARS CIGS AND VIS WITH SHRA AND SOME TSRA SHOULD GENERALLY REMAIN IN THE VFR RANGE...THOUGH SOME BRIEF MVFR IS POSSIBLE IN SOME OF THE STRONGER SHOWERS OR STORMS. AS THE FRONT MOVES INTO THE REGION AND THE NOCTURNAL INVERSION MIXES OUT... LIGHT WINDS SHOULD BECOME SOUTHWEST TO WEST WINDS AND INCREASE TO AROUND 10KT FOR THE TAF SITES BY AROUND 15Z...WITH SOME GUSTS UP TO 20KT POSSIBLE...ESPECIALLY 16Z TO 22Z. WINDS WILL BECOME MORE NORTHWESTERLY BEHIND THE FRONT GENERALLY 21Z THROUGH 0Z AND AS THE PRESSURE GRADIENT RELAXES WINDS SHOULD DECREASE TO BELOW 10KT LATE IN THE PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...KAS LONG TERM...JMW AVIATION...JP

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