Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 291202
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
802 AM EDT MON SEP 29 2014

.UPDATE...
ISSUED AT 802 AM EDT MON SEP 29 2014

REFRESHED GRIDS TO REFLECT EARLY MORNING OBS BLENDING INTO THE LATE
MORNING FORECAST.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 357 AM EDT MON SEP 29 2014

SHOWERS FALLING FROM A HIGH CLOUD BASE WERE NEAR THE KY/VA BORDER
OVERNIGHT. THIS REGIME IS EXPECTED TO MOVE OUT TO THE SOUTHEAST
EARLY MONDAY MORNING. AFTER A LULL...THERE WILL BE A POTENTIAL FOR
MORE SHOWERS TO DEVELOP DURING THE DAY AS HEATING LEADS TO SHALLOW
INSTABILITY. IT SHOULD BE CAPPED AROUND 650 MB. THIS LEVEL IS TOO
WARM FOR GLACIATION OF CLOUD TOPS...BUT ALLOWS FOR A DEEP ENOUGH
CLOUD TO PERHAPS GET SOME LIGHT SHOWERS OR SPRINKLES. THESE WILL DIE
OUT WITH LOSS OF HEATING MONDAY EVENING. DURING THE NIGHT...SLIGHTLY
DRIER AIR IS EXPECTED TO ARRIVE IN THE LOWER LEVELS...WHILE SLIGHT
WARMING OCCURS IN THE MID LEVELS. THIS WILL KEEP TUESDAY DRY AND
MOSTLY SUNNY WITH LITTLE OR NO CU DEVELOPMENT.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 357 AM EDT MON SEP 29 2014

MODELS ARE STARTING TO WAVER A BIT WITH AN EXPECTED COLD FRONT ON
FRIDAY...BUT OVERALL STILL IN AGREEMENT ON WIDESPREAD SHOWERS FOR
EASTERN KENTUCKY AS IT PUSHES ACROSS THE AREA. MODELS ARE ALSO
DIVERGING ON POSSIBLE SOLUTIONS HEADING THROUGH NEXT WEEKEND.
THUS...WHILE CONFIDENCE REMAINS HIGH ON PRECIPITATION
CHANCES...CONFIDENCE IS DEGRADED AROUND THE TIMING OF THE RAIN LATE
IN THE WEEK...THEN EXACTLY HOW COLD/CLOUDY IT WILL END UP THIS
WEEKEND.

THE PERIOD WILL START WITH SFC HIGH PRESSURE IN CONTROL...SETTING UP
DRY AND MILD CONDITIONS INTO THE DAY ON THURSDAY. A SHARP MID LEVEL
TROUGH AXIS WILL THEN PUSH ACROSS THE AREA THURSDAY NIGHT INTO
FRIDAY...DRAGGING A WEAK COLD FRONT ACROSS THE AREA. GOOD UPPER
LEVEL DIVERGENCE...COMBINED WITH GOOD LOW LEVEL CONVERGENCE SHOULD
PROVIDE PLENTY OF SUPPORT FOR WIDESPREAD SHOWERS. WHILE INSTABILITY
IS WEAK...FORCING MAY BE STRONG ENOUGH JUST AHEAD OF THE FRONT TO
PRODUCE A LIGHTNING STRIKE AS IT PUSHES ACROSS THE AREA. THUS...WILL
MAINTAIN THE SLIGHT CHANCE OF THUNDERSTORMS. THE 00Z ECMWF SUPPORTS
THE 12Z RUN WITH A FASTER SYSTEM...BRINGING PRECIPITATION IN FASTER
THURSDAY NIGHT...WITH EVERYTHING EXITING EARLIER ON FRIDAY.
HOWEVER...THE 00Z GFS HAS ALSO REMAINED SUPPORTIVE OF A SLOWER
SYSTEM...WITH MORE PRECIPITATION OCCURRING ON FRIDAY. THUS...WILL
MAINTAIN A LONGER PERIOD OF HIGHER POPS TO ACCOUNT FOR THIS
UNCERTAINTY. REGARDLESS...THIS SYSTEM SHOULD PRODUCE DECENT LIGHT TO
MODERATE RAINFALL ACROSS THE AREA.

AS THE INITIAL FRONT DEPARTS...A SECONDARY COLD FRONT WILL BRING A
SURGE OF MUCH COLDER WEATHER INTO THE AREA FOR THE START OF THE
UPCOMING WEEKEND AS A 500MB VORT MAX PUSHES ACROSS THE GREAT LAKES.
THE 00Z ECMWF CUTS OFF THIS SYSTEM...WITH A MUCH SHARPER TROUGH
PUSHING SOUTH INTO THE OHIO RIVER VALLEY. THIS SCENARIO WOULD
SUPPORT MORE CLOUDS AND MUCH COOLER READINGS. MEANWHILE...THE GFS
DOES NOT CUT OFF THIS SYSTEM...AND IS MUCH WEAKER WITH THE TROUGH.
GIVEN WE ARE HEADING INTO THE COLD SEASON...TENDENCY IS TO WANT TO
SUPPORT THE SHARPER TROUGH SEEN IN THE ECMWF AS THE PATTERN WOULD BE
SUPPORTIVE FOR THIS TIME OF THE YEAR. THUS...STAYING WELL BELOW
GUIDANCE ON HIGHS AND LOWS FROM SATURDAY THROUGH SATURDAY NIGHT. IF
THINGS PLAY OUT AS THE ECMWF SUPPORTS...WE MAY STRUGGLE TO REACH 60
ON SATURDAY WITH LOWS SATURDAY NIGHT INTO THE UPPER 30S/LOWER 40S.
AT THIS TIME...REGARDLESS WHICH SOLUTIONS PLAYS OUT...FROST APPEARS
UNLIKELY AS THE COLDER ECMWF WOULD SUPPORT MORE CLOUD COVER...AND
THE GFS SIMPLY WOULD NOT BE COLD ENOUGH. IN FACT... THE ECMWF MAY
SUPPORT A FEW RAIN SHOWERS ON SATURDAY OR SATURDAY NIGHT AS A VORT
MAX DROPS SOUTH INTO THE OHIO RIVER VALLEY. GOING TO LEAVE THINGS
DRY FOR NOW...BUT MAY NEED TO ADD SOME RAIN CHANCES IF THE ECMWF
GAINS SUPPORT. BY SUNDAY...WE SHOULD SEE THE AIR MASS PERHAPS START
TO MODIFY WITH TEMPERATURES REBOUNDING BACK INTO THE MID TO UPPER
60S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 802 AM EDT MON SEP 29 2014

CONDITIONS VARIED WIDELY AT THE START OF THE PERIOD. MANY LOCATIONS
WERE IFR OR WORSE DUE TO FOG. AREAS WHICH TEND TO BE MORE DIFFICULT
TO FOG IN WERE LARGELY VFR. FOG WILL DISSIPATE BY LATE THIS
MORNING...LEAVING VFR TO LAST INTO TONIGHT. A FEW SHOWERS MAY
DEVELOP AFTER HEATING TAKES PLACE TODAY...THEN DIE OUT TOWARD
EVENING. HOWEVER...ANY SHOWERS WILL BE LIGHT. VALLEY FOG IS LIKELY
AGAIN TONIGHT...SPREADING IN COVERAGE OVERNIGHT.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...HAL
SHORT TERM...HAL
LONG TERM...KAS
AVIATION...HAL





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