Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 180610 AAC AFDJKL AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON KY 210 AM EDT THU SEP 18 2014 .UPDATE...
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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.
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&& .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...
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(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.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...GREIF LONG TERM...HAL AVIATION...JP

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