Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 180610 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
210 AM EDT THU SEP 18 2014

.UPDATE...
ISSUED AT 145 AM EDT THU SEP 18 2014

SCT TO BKN MAINLY MID LEVEL CLOUDS ASSOCIATED WITH AN APPROACHING
DISTURBANCE CONTINUE TO WORK EAST ACROSS THE COMMONWEALTH. MODEL 700
MB MOISTURE PLAN VIEW DATA SUGGESTS THAT THIS WILL CONTINUE TO WORK
EAST ACROSS THE REGION DURING THE REMAINDER OF THE OVERNIGHT HOURS
AND INTO EARLY ON THURSDAY WITH HIGHER CHANCES FOR BROKEN OR
OVERCAST MID LEVEL CLOUDS ACROSS THE CENTRAL AND SOUTHERN PARTS OF
THE CWA AND MORE OF A CHANCES FOR SCATTERED MID CLOUDS OR SCATTERING
OUT TOWARD DAWN IN THE FAR NORTH. MEANWHILE...FOG HAS DEVELOPED
ESPECIALLY IN THE VALLEY LOCATIONS...BUT WITH MID CLOUDS WORKING IN...
IT EITHER SHOULD NOT BECOME DENSE OR IF IT DOES SO IT MAY BECOME LESS
DENSE TOWARD DAWN OR DURING PERIODS WHEN THE MID CLOUDS ARE WORKING
OVERHEAD. THERE REMAINS UNCERTAINTY WITH THE DETAILS OF THE FOG AND
ALSO THE HOURLY TEMPERATURE CURVE AS WELL. AT THIS POINT...HOURLY
GRIDS HAVE BEEN UPDATED BASED ON RECENT SAT AND OBSERVATION TRENDS
AND BLENDED INTO THE PREVIOUS FORECAST TOWARD DAWN.

UPDATE ISSUED AT 1025 PM EDT WED SEP 17 2014

FORECAST APPEARS ON TRACK THIS EVENING. MOISTURE ASSOCIATED WITH
WEAKENING DISTURBANCE IS TRACKING TOWARDS OUR AREA AS EXPECTED.
RESULT WILL BE SCT TO AT TIMES BKN SKY COVER...MAKING DETAILS OF
HOURLY TEMPERATURE FORECAST AND FOG DEVELOPMENT ALL THAT MORE
CHALLENGING THROUGH THE REMAINDER OF THE OVERNIGHT PERIOD. TWEAKED
AND BLENDED GRIDS TOWARDS HOURLY OBS AND TRENDS. ATTM...NO OTHER
CHANGES TO THE FORECAST PACKAGE ARE NECESSARY.

UPDATE ISSUED AT 835 PM EDT WED SEP 17 2014

A WEAK DISTURBANCE ALOFT IS MOVING SOUTHEAST OUT OF THE UPPER
MIDWEST. SOME LIGHT TO MODERATE SHOWER ACTIVITY OVER SOUTHERN IL/IN
IS DISSIPATING AS THE DISTURBANCE WEAKENS. HOWEVER...THIS FEATURE
WILL STILL BE STRONG ENOUGH TO BRING IN SOME ADDITIONAL MID LEVEL
CLOUDINESS TO OUR AREA FOR A PERIOD OF TIME OVERNIGHT. QUESTION IS
WILL CLOUD COVER BE WIDESPREAD ENOUGH TO MITIGATE FORMATION OF FOG.
TEMPERATURES ARE DROPPING AT A DECENT RATE AS OUR CU FILED
DISSIPATES. SFC DEW POINTS HAVE ALREADY REBOUNDED AS WELL. THOUGHTS
ARE WE WILL SEE SOME PATCHY FOG DEVELOPING THROUGH THE EVENING TIME
FRAME. BUT DENSITIES AND COVERAGE MAY BE LIMITED AS CLOUDS ROLL
THROUGH GENERALLY BETWEEN 05Z AND 10Z. APPEARS THERE MAY BE SOME
PARTIAL CLEARING AS WE APPROACH SUNRISE WHERE FOG COULD THICKEN UP
AND SPREAD FOR THOSE COUPLE OF HOURS AROUND DAWN. MUCH DEPENDS ON
EXACTLY HOW MUCH CLOUD COVER WE REALIZE. WITH DEW POINTS RECOVERING
SO QUICKLY AND TEMPERATURES DROPPING FASTER THAN EXPECTED...FELT IT
WOULD BE GOOD TO INTRODUCE THE DEVELOPMENT OF SOME PATCHY FOG THROUGH
THE EVENING HOURS...AND EARLY MORNING THURSDAY. THEREAFTER EXPANDED
FOG THROUGH THE PREDAWN HOURS. MAY SOME TWEAKS TO OVERNIGHT LOWS
BASED ON HOURLY TRENDS. THIS RESULTED IN A DROP OF A FEW DEGREES...
MAINLY IN OUR NORTH.

&&

.SHORT TERM...(THIS EVENING THROUGH THURSDAY NIGHT)
ISSUED AT 335 PM EDT WED SEP 17 2014

18Z SFC ANALYSIS SHOWS WEAK HIGH PRESSURE IN PLACE OVER EAST
KENTUCKY WITH A WAVY FRONT TO THE SOUTH OF THE STATE. ALONG THE
WESTERN EXTENT OF THIS BOUNDARY...A WAVE HAS DEVELOPED AND IS
RUNNING SOUTHEAST OVER THIS FRONT COMING OUT OF SOUTHEAST MISSOURI.
LOCALLY THE CLOUDS ARE BREAKING UP THROUGH THE SOUTHWEST PORTIONS OF
THE CWA...WHILE HOLDING ON A BIT LONGER OVER THE NORTHEAST.
TEMPERATURES VARY MAINLY ACCORDING TO THE AMOUNT OF AFTERNOON
SUNSHINE...FROM THE MID 60S NORTHEAST TO THE LOWER 70S IN THE SOUTH.
DEW POINTS ARE GENERALLY IN THE LOW AND MID 50S THROUGH THE AREA WITH
LIGHT AND VARIABLE WINDS IN PLACE.

THE MODELS ARE IN GOOD AGREEMENT ALOFT AS THEY WEAKEN THE LARGE
NORTHEAST TROUGH THAT HAS BEEN IN PLACE FOR NEARLY A WEEK NOW. A
FEW WEAK SHORT WAVES WILL PASS THROUGH THE OHIO VALLEY DURING THIS
FILLING PROCESS. ANY MODEL DIFFERENCES THAT CROP UP WILL HAVE
RELEVANCE ONLY AFTER THE SHORT TERM PART OF THE FORECAST.
ACCORDINGLY...HAVE FOLLOWED A GENERAL MODEL BLEND AND FOCUSED ON THE
LOWER LEVEL MOISTURE OVER THE NEXT 36 TO 42 HOURS AS DEPICTED IN THE
HIGHER RESOLUTION NAM12 AND ALSO...INITIALLY...THE HRRR.

SENSIBLE WEATHER WILL FEATURE THE SFC REFLECTION...OF THE MID LEVEL
WAVE...PASSING JUST TO THE SOUTH OF THE AREA THIS EVENING WITH
MAINLY JUST AN INCREASE IN CLOUDS NOTED FOR EAST KENTUCKY. THESE
CLOUDS WILL CLEAR OUT...AS WELL...AFTER MIDNIGHT SETTING THE STAGE
FOR A NIGHT OF GOOD RADIATIONAL COOLING THAT SHOULD RESULT IN SOME
UPPER 40S IN THE NORTHERN VALLEYS BY DAWN ALONG WITH AREAS OF
FOG...LOCALLY DENSE TOWARD SUNRISE. IN THE WAKE OF THE SFC WAVE...
THURSDAY WILL SEE A RESURGENT HIGH BUILD INTO EAST KENTUCKY FROM THE
NORTH WHILE THE CLOUDS MOVE OFF TO THE SOUTH. ANY CAA WITH THIS WILL
BE COUNTERACTED BY THE AMPLE SUNSHINE TO YIELD COMFORTABLE
TEMPERATURES SIMILAR TO THOSE OF TODAY...ONCE THE FOG CLEARS.
ANOTHER GOOD NIGHT OF RADIATIONAL COOLING FOLLOWS THURSDAY NIGHT WITH
PATCHY VALLEY FOG...OR WORSE...ANTICIPATED BY DAWN WHILE TEMPS WILL
FLIRT WITH THE UPPER 40S AGAIN IN THOSE VALLEYS. BOTH TONIGHT AND
THURSDAY NIGHT...SLIGHTLY MILDER READINGS CAN BE EXPECTED ON THE
RIDGES.

THE CONSSHORT WAS USED AS A STARTING POINT FOR THE T/TD/WIND GRIDS
THROUGH THE FIRST 24 HOURS BEFORE THE SUPER BLEND WAS LOADED IN
THEREAFTER. DID AGAIN NUDGE THE LOWS TONIGHT...AND THURSDAY NIGHT...
FOR RIDGE AND VALLEY DIFFERENCES. AS FOR POPS...ENDED UP WITH SINGLE
DIGITS THROUGH THE FORECAST...IN-LINE WITH GUIDANCE.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 200 PM EDT WED SEP 17 2014

A DRY AIR MASS WILL STILL BE IN PLACE AS THE PERIOD STARTS...WITH
SPRAWLING SURFACE HIGH PRESSURE OVER NEW ENGLAND RIDGING
SOUTHWESTWARD...AND A COLD FRONT OVER THE HIGH PLAINS. GREATER LOW
LEVEL MOISTURE WILL BE LOOMING JUST SOUTHEAST OF THE APPALACHIANS.
MODELS SHOW SOME OF THIS MOISTURE MAKING ITS WAY INTO KY IN THE FLOW
AROUND THE HIGH ON FRIDAY. THE GFS AND ECMWF EVEN SHOW PRECIP AS FAR
NW AS OUR EASTERN AND SOUTHEASTERN BORDER. HOWEVER...THE GFS MOS IS
LESS THAN 20 PERCENT POP AND THE NAM IS DRY...SO WILL STAY WITH A
DRY FORECAST ON FRIDAY. A WEAKENING UPPER RIDGE WILL MOVE EAST OVER
THE REGION FRIDAY NIGHT AND SATURDAY...AHEAD OF AN AMPLIFYING TROUGH
DROPPING SOUTH FROM CANADA. THE WARMING ALOFT THAT IT BRINGS WILL
RESULT IN A STABLE ATMOSPHERE...DESPITE SURFACE DEW POINTS AND
TEMPERATURES CONTINUING TO CREEP HIGHER.

THE TROUGH WILL CONTINUE ITS AMPLIFICATION AND SOUTHEASTWARD
PROGRESS...BRINGING THE AFOREMENTIONED COLD FRONT INTO THE OHIO
VALLEY ON SUNDAY. THE FRONT SHOULD EVENTUALLY PASS THROUGH THE JKL
FORECAST AREA...BUT MODELS ARE STILL NOT LOCKED IN ON SIMILAR
TIMING. A MODEL BLEND WOULD SUGGEST SUNDAY EVENING...AND WILL
CENTER THE HIGHEST POPS AT THAT TIME...BUT WITH TEMPORAL VARIABILITY
IN MODELS...WILL USE AN EXTENDED PERIOD OF POPS WITH NOTHING ABOVE
CHANCE CATEGORY AT THIS POINT. ONCE THE SYSTEM PASSES...ANOTHER
LARGE...COOL...AND DRY SURFACE HIGH PRESSURE SYSTEM IS EXPECTED TO
PASS SLOWLY BY JUST TO OUR NORTH...BRINGING AUTUMN-LIKE WEATHER FOR OUR
LOCAL AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 155 AM EDT THU SEP 18 2014

A WEAK DISTURBANCE IS MOVING SOUTHEAST TOWARD THE LOWER OH VALLEY
REGION. THIS FEATURE IS BRINGING SOME MID LEVEL MOISTURE AND CLOUDS TO
THE COMMONWEALTH AND SOME OF IT IS WORKING INTO THE CWA ATTM. THIS
CLOUD COVER SHOULD GENERALLY TEND TO MODERATE OR LIMIT FOG DEVELOPMENT
OVERNIGHT. FOG HAS DEVELOPED...ESPECIALLY ACROSS THE SOUTHEAST PART
OF THE CWA NEAR SJS. PENDING ANY PARTIAL CLEARING THERE MAY BE MORE
COVERAGE CLOSE TO DAWN...BUT RECENT TRENDS POINT TOWARD THIS ACROSS
THE FAR NORTH AND THE NEXT COUPLE OF HOURS IN THE SOUTHEAST. UNCERTAINTY
REMAINS IN THE FOG OVERNIGHT...BUT GUIDANCE HAS GENERALLY TRENDED
TOWARD LESS FOG AT JKL AND LOZ. THIS TREND SHOULD ALSO HOLD FOR SME
AND SJS AS THE CLOUDS SHOULD RESTRICT OR LIMIT FOG DEVELOPMENT UNLESS
BREAKS OR PARTIAL CLEARING DEVELOPS. DENSITY AND COVERAGE OF FOG WILL
DEPEND ON EXACTLY HOW MUCH CLOUD COVER WE REALIZE. FOR THE TAF SITES
WE HAVE OPTED TO GO AS OPTIMISTIC...IF NOT A BIT MORE OPTIMISTIC THAN
MODEL GUIDANCE WOULD SUGGEST. THIS BROUGHT VIS DOWN TO NO WORSE THAN
IFR AT THE TAF SITES GENERALLY DURING THE 8Z TO 14Z PERIOD. WINDS
WILL BE LIGHT THROUGH THE PERIOD.

&&

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

$$

UPDATE...JP
SHORT TERM...GREIF
LONG TERM...HAL
AVIATION...JP





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