Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 210635 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
235 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 THROUGH SATURDAY)
ISSUED AT 311 PM EDT SAT SEP 20 2014

THE MODELS ARE IN GOOD AGREEMENT WITH AN AMPLIFIED LONG WAVE PATTERN
TO AFFECT THE CONUS THROUGH THE PERIOD. AN UPPER LEVEL TROUGH WILL
START OFF MOVING IN ACROSS THE EASTERN CONUS...WITH RIDGING IN THE
PLAINS...AND DEEP TROUGHING IN THE EASTERN PACIFIC. SMALLER SCALE
FEATURES WITHIN THE BROADER FLOW ARE AS USUAL MORE DIFFICULT TO NAIL
DOWN THIS FAR OUT. THE GFS AND ECMWF HAVE SOME DISAGREEMENT WITH
REGARD TO THESE DETAILS...AND THIS DOES AFFECT THE OUTCOME OF THE
LONG WAVE TOWARDS NEXT WEEKEND. THE EASTERN PACIFIC TROUGH WILL SLAM
INTO THE WESTERN CONUS THROUGH THE END OF THE WORK WEEK...HELPING TO
AMPLIFY THE DOWNSTREAM RIDGE...WHICH WILL TAKE UP RESIDENCE ACROSS
THE MAJORITY OF THE MISSISSIPPI VALLEY. THERE WILL BE SOME WEAKNESS
ON THE UPSTREAM AND DOWNSTREAM SIDE OF THIS RIDGE AXIS.

THE MODELS DISAGREE ON THIS POINT...WITH THE ECMWF PUTTING MORE
EMPHASIS ON THE WEAKNESS OF THE RIDGE DOWNSTREAM...WHICH EVENTUALLY
BECOMES A CUTOFF LOW THAT WILL FORM ACROSS THE MID-ATLANTIC
REGION. THE GFS HAS MORE WEAKNESS ESTABLISHED UPSTREAM...WITH
TROUGHING DEVELOPING ACROSS THE PLAINS...KEEPING THE RIDGE MORE
ESTABLISHED IN THE EASTERN CONUS. GIVEN ALL OF THIS UNCERTAINTY...
WILL STICK CLOSE TO THE BLENDED GUIDANCE...ESPECIALLY SINCE THE
RESULTANT SURFACE FEATURES LOOK MORE BENIGN EITHER WAY FOR OUR
REGION FOR NOW.

FOR EASTERN KENTUCKY...VERY PLEASANT WEATHER WILL BE ON TAP FOR THE
PERIOD...AS SURFACE HIGH PRESSURE REMAINS ANCHORED OFF TO THE NORTH
AND NORTHEAST. TEMPERATURES WILL START OUT BELOW NORMAL THROUGH THE
MIDDLE OF NEXT WEEK...WITH HIGHS IN THE LOW TO MID 70S AND LOWS IN
THE 40S. READINGS WILL THEN GRADUALLY MODIFY THROUGH THE REST OF THE
PERIOD...WITH HIGHS NEARING THE 80 DEGREE MARK BY THE START OF THE
WEEKEND. LOWS WILL MAINLY BE IN THE 50S.

&&

.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...GEOGERIAN
AVIATION...JP






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