473
FXUS63 KJKL 210555 AAA
AFDJKL
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
1255 AM EST SAT NOV 21 2009
SHORT TERM
/THE REST OF TONIGHT/
RATHER DENSE LAYER OF CIRRUS STREAMING INTO THE AREA FROM THE SW.
DWPTS ARE RUNNING HIGHER THAN LAST NIGHT. COMBINATION OF THESE TWO
FACTORS WILL PROMOTE LOW TEMPS THAT ARE WARMER THAN LAST NIGHT...BUT
STILL COOL ENUF TO ALLOW THE FORMATION OF VALLEY FOG. RIDGE VALLEY
SPLIT HAS ALREADY BEGUN AND SHOULD CONTINUE OVERNIGHT. ALL THIS
COVERED IN CURRENT FCST...SO NO UPDATED PLANNED. MINOR TWEAKS TO LOW
TEMPS WILL NOT CHANGE ZONE WORDING.
THE PREVIOUS SHORT TERM FORECAST DISCUSSION FOLLOWS...
/TONIGHT THROUGH SUNDAY NIGHT/
SFC HIGH PRESSURE WAS LOCATED OVER THE OH RIVER VALLEY THIS
AFTERNOON WITH RIDGING WEST INTO THE MID MS VALLEY. OVER THE WESTERN
GULF OF MEXICO AN AREA OF LOW PRESSURE WAS BEGINNING TO DEVELOP
ASSOCIATED WITH AN UPPER LEVEL TROUGH MOVING THROUGH THE SOUTHERN
PLAINS. FURTHER NORTH ANOTHER UPPER LEVEL TROUGH EXTENDED SOUTHWEST
TO THE MID MS VALLEY...WITH ANOTHER UPPER LEVEL LOW WELL TO THE
NORTHEAST MOVING THROUGH THE NORTHEAST AND ST LAWRENCE VALLEY. THE
DIURNALLY DRIVEN CU APPEAR TO BE MIXING OUT AT THIS TIME. DEWPOINTS
OVER THE EASTERN CWA HAVE FALLEN TO THE MID AND UPPER 30S...WITH
DEWPOINTS AROUND 40 IN THE WEST. SOME FURTHER MIXING IN THE NEXT HOUR
OR SO MAY BRING THE DEWPOINTS IN THE SW AND CROSSOVER TEMP ANOTHER
DEGREE OR TWO.
THE MORE NORTHERN TROUGH WILL MOVE INTO THE OH VALLEY TONIGHT AND EXIT
ON SAT...BUT HAVE VERY LITTLE EFFECT ON THE WEATHER OTHER THAN BRING
AN INCREASE IN CIRRUS. THIS TREND CAN ALREADY BE OBSERVED IN SAT
IMAGERY WITH CIRRUS ADVANCING TOWARD THE REGION FROM THE WEST AND
SOUTHWEST. AT THIS POINT...THOUGH THERE ARE MODEL DIFFERENCES BETWEEN
THE 12Z GFS AND 12Z NAM IN HOW THICK THE CIRRUS WILL BE...THE AFFECT
ON RADIATIONAL COOLING TONIGHT IS EXPECTED TO NEGLIGIBLE. WITH THE SFC
HIGH PRESSURE RIDGE PROGGED TO SHIFT GRADUALLY ENE OVERNIGHT WITH ITS
AXIS TO BE ALIGNED FROM KLAF TO NEAR IND...LIGHT WINDS ARE EXPECTED...
ESPECIALLY IN THE EASTERN VALLEYS. WITH THIS IN MIND...FEEL THAT
ANOTHER RIDGE VALLEY SPLIT WITH VALLEYS GETTING INTO THE LOWER 30S
SHOULD OCCUR IN THE EAST...WITH RIDGETOPS AROUND 40. HAVE MOS UNDERCUT
GUIDANCE A COUPLE OF DEGREES ACROSS THE BOARD DUE TO THE FACT THAT IT
RAN ON THE WARM SIDE YESTERDAY. THIS PATTERN SHOULD ONCE AGAIN LEAD
TO AT LEAST PATCHY VALLEY FOG. THE FOG MAY BE MOST PREVALENT IN THE
BIG SANDY AND CUMBERLAND RIVER VALLEYS. VISIBILITIES IN LOCATIONS
THAT EXPERIENCE VALLEY FOG COULD BE REDUCED BELOW ONE MILE IN A FEW
LOCATIONS LATE TONIGHT. WE PLAN TO ADD THE THREAT OF FOG LATE TONIGHT/
EARLY SAT TO THE HWO.
THE MAIN DISPARITY IN THE PATTERN FROM SAT AM ON IS THE OVERALL TRACK
AND TIMING OF A SFC LOW MOVING THROUGH THE SOUTHEASTERN STATES WITH
REORGANIZATION ALONG THE EAST COAST AROUND THE END OF THE PERIOD.
THERE ARE ALSO DIFFERENCES IN THE TIMING...DEPTH AND PATH OF THE
UPPER LEVEL LOW THAT OPENS TO AN OPEN WAVE AS IT MOVES TOWARD THE OH
VALLEY REGION SUN AND INTO THE UPPER OH VALLEY BY THE END OF THE
PERIOD. THE LAST COUPLE OF GFS RUNS TEND TO BE ON THE QUICKER END OF
THE SPECTRUM WITH THE TIMING AND CLOSER TO THE CWA WITH THE DAMPENING
WAVE SUN/SUN NIGHT...WHILE THE NAM...AT LEAST THE 12Z NAM IS WEAKER
AND AT THE SLOWER END OF THE SPECTRUM. PRECIP CHANCES ARE ALSO
TRICKY AS THE GFS CONTINUES TO BRING PRECIP INTO THE AREA...WHILE
THE GFS REMAINS CONSIDERABLY DRIER. THE 12Z CANADIAN ALSO BRING SOME
PRECIP INTO THE CWA...BUT IS ALSO LATER THAN THE 12Z GFS. THE 12Z
ECMWF IS ALSO ON THE SLOWER END OF THE SPECTRUM...BUT DOES BRING SOME
LIGHT PRECIP INTO THE AREA BY 0Z SUN.
THIS PATTERN WILL LIKELY LEAD TO A WEAK SFC REFLECTION OF THE TROUGH
EXTENDING NORTH IN THE CWA BY LATE SAT OR SAT NIGHT...AS IS OFTEN
THE CASE. OVERALL...INCREASING...THICKENING AND LOWERING CLOUDS ARE
EXPECTED ON SAT AND INTO SAT NIGHT. THERE MAY BE SOME GENERAL LIGHT
RAIN OVER THE AREA AS THE UPPER LEVEL TROUGH APPROACHES AND
PASSES...WITH PRECIP MORE ASSOCIATED WITH THE SFC LOW PERHAPS
BRUSHING SOUTHERN AND SOUTHEASTERN AREAS AS WAS NOTED BY THE PREVIOUS
FORECASTER. WITH ALL THE DISPARITY AMONG THE MOS POPS AS BETWEEN THE
MOS POPS AND 15Z SREF POPS...OPTED TO GENERALLY STAY CLOSE TO
PERSISTENCE WITH POPS FOR SAT NIGHT AND SUN...SLOWING DOWN THE
NORTHWARD EXTENT OF POPS A TAD ON SAT NIGHT. EVEN IF THE DRIER 12Z
NAM WERE TO VERIFY...FELT THAT IT WOULD BE PRUDENT TO HOLD THE LINE
ON POPS FOR NOW...WITH LATER SHIFTS POSSIBLY SHIFTING THEM SLIGHTLY
LATER IF NEEDED BASED ON SUCCESSIVE MODEL CYCLES AND TRENDS. THIS LED
TO GOOD CHANCE POPS IN THE MORE SOUTHERN LOCATIONS AND SLIGHT CHANCE
TO CHANCE IN THE NORTH FOR SUN AND SUN NIGHT. MOS GUIDANCE TRENDED A
LITTLE BIT WARMER FOR HIGHS ON SAT...AND RAISED MAX T A DEGREE OR TWO
IN MOST AREAS...ESPECIALLY CONSIDERING THAT IT IS NOW IN THE LOWER
60S IN THE FAR SOUTH AND 8H TEMPS SHOULD AVERAGE SLIGHTLY WARMER ON
SAT.
WITH CLOUDS AND PRECIP ANTICIPATED...OPTED TO GO KEEP TEMPS IN LINE
WITH THE PREVIOUS FORECAST/MAV GUIDANCE FOR SAT NIGHT AND SUN...THOUGH
ALLOWED FOR MORE EASTERN AND NORTHEASTERN VALLEY LOCATIONS TO COOL
OFF A COUPLE OF DEGREES MORE THAN THE PREVIOUS FORECAST ON SAT NIGHT.
LONG TERM
/MONDAY THROUGH FRIDAY/
THE LONG RANGE MODELS AGAIN ARE SHOWING SOME DISAGREEMENT REGARDING
THE PASSAGE OF TWO AREAS OF LOW PRESSURE NEXT TUESDAY AND THURSDAY.
OVERALL THE GFS HAS BEEN THE MOST CONSISTENT MODEL IN RECENT DAYS
REGARDING THE HANDLING OF THE OVERALL SYNOPTIC PATTERNS...SO ITS
SOLUTION WAS PREFERRED. THE OVERALL PRECIPITATION FORECAST WAS
UPDATED USING THE LATEST GFS RUN AND A BLEND OF THE 0 AND 12Z RUNS
OF MEXMOS. THE RESULTING CHANGES WERE AS FOLLOWS, LONGER AND MORE
DISTINCT BREAKS BETWEEN PRECIPITATION EVENTS WERE INCORPORATED INTO
THE FORECAST PER THE LATEST GFS...AS THE PATTERN LOOKS TO BRING A
WEAK FRONT ACROSS THE FORECAST AREA...WITH PERHAPS LESS OF A WRAP
AROUND MOISTURE UPSLOPE FLOW TYPE OF PATTERN. QPF NUMBERS WERE ABOUT
THE SAME AS BEFORE...WITH ADJUSTMENTS TOWARD THE NEWLY INTRODUCE
TIMING OF FRONTAL PASSAGE. WITH A FRONTAL TYPE PRECIP EVENT EXPECTED
NEXT WEEK...ALSO DECREASED THE OVERALL AREAL COVERAGE OF PRECIP FOR
TUESDAY AND TUESDAY NIGHT. THE PATTERN FOR NEXT THURSDAY INTO FRIDAY
WAS TWEAKED AS WELL...BUT ONLY MINIMALLY AT THIS POINT. STILL
DECIDED AGAINST INTRODUCING ANY WINTRY TYPE PRECIP INTO THE FORECAST
FOR NEXT THURSDAY NIGHT DUE TO THE AMOUNT OF UNCERTAINTY IN THE
MODEL DATA AND GUIDANCE THAT FAR OUT.
WITH THE PREVIOUS TWO RUNS OF THE MEXMOS COMING IN WITH TEMPERATURES
WARMER THAN FORECAST...DECIDED TO INCREASE DAYTIME HIGHS BY A TWO OR
THREE DEGREES EACH DAY EXCEPT WEDNESDAY...WHILE STILL GOING SLIGHTLY
COOLER THAN THE WARMER 12Z RUN OF MEXMOS TO ACCOUNT FOR CLOUD COVER
AND COOLING EFFECT OF WESTERLY AND NORTHWESTERLY WINDS. OVERNIGHT
LOWS WERE WARMED A BIT AS WELL...GOING JUST ABOVE MEXMOS NUMBERS AS
PERSISTENT LOW AND MIDDLE LEVEL CLOUD COVER ARE EXPECTED TO PERSIST
DURING THE OVERNIGHT PERIODS NEXT WEEK.
AVIATION.../06Z TO 06Z/
UPDATED
ASIDE FROM THE POSSIBILITY OF LATE NIGHT MVFR TO IFR FOG IN THE
DEEPER VALLEYS TOWARD DAWN...VFR CONDITIONS WILL BE THE RULE THROUGH
THE TAF PERIOD AS HIGH PRESSURE KEEPS THE AREA CLEAR BELOW 12K FEET.
JUST A SCT TO BKN LAYER OF HIGH CLOUDS OF VARYING THICKNESS IS
EXPECTED THROUGH SATURDAY MORNING. HAVE KEPT THE HIGHEST THREAT OF
IFR FOG IN THE SME TAF WITH A LONGER PERIOD OF MVRF FOG EXPECTED...
COMPARED TO LOZ...WHILE JKL WILL NOT SEE ANY FOG. WINDS WILL BE
LIGHT...GENERALLY FROM THE NORTHEAST THROUGH THE PERIOD.
JKL WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...JP/DUSTY
LONG TERM....AR
AVIATION...GREIF
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