Area Forecast Discussion
Issued by NWS Jackson, KY

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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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