FXUS63 KJKL 120241
AFDJKL
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
941 PM EST FRI DEC 11 2009
.SHORT TERM.../THE REST OF TONIGHT/...UPDATED
FORECAST IS ON TRACK THIS EVENING. LOOKING FOR COLD TEMPERATURES
THROUGH THE OVERNIGHT WITH CLEAR SKIES AND LIGHT TO CALM WINDS AS 24
HOUR TEMPS TREND ARE AT...OR ONLY SLIGHTLY WARMER THAN LAST NIGHT.
EXCEPTION TO THIS ARE OUR THERMAL BELT RIDGES WHICH ARE RUNNING
ABOUT 5 TO 7 DEGREES WARMER. HOWEVER...STILL EXPECT THE THERMAL BELT
TO EVENTUALLY MAKE OUR ORIGINALLY FORECASTED LOWS AS THE NOCTURNAL
INVERSION BUILDS ABOVE THE THERMAL BELT LEVEL JUST BEFORE SUNRISE...
ESPECIALLY WITH 18Z MOS GUIDANCE COMING IN 6 DEGREES COLDER THAN THE
12Z NUMBERS AT JKL WHICH IS A BEST REPRESENTATION OF THERMAL BELT
TEMPERATURES IN GENERAL. SO MADE SOME TWEAKS TO THE THERMAL BELT...
HOLDING ONTO WARMER TEMPS FOR SEVERAL MORE HOURS BEFORE DROPPING THEM
OFF JUST BEFORE SUNRISE. OTHERWISE...INCREASED LOWS A DEGREE...MAYBE
TWO IN VALLEYS JUST TO OUR WEST TO ACCOUNT FOR HIGHER THAN EXPECTED
DEW POINTS FOR LOCATIONS IN THE KENTUCKY RIVER VALLEY. UPDATED ISC
GRID PRODUCTS OUT ASAP. NO UPDATES PLANNED FOR THE ZONE PRODUCT ATTM.
THE PREVIOUS SHORT TERM FORECAST DISCUSSION FOLLOWS...
/TONIGHT THROUGH SUNDAY NIGHT/
AN AREA OF HIGH PRESSURE CURRENTLY CENTERED ACROSS THE TENNESSEE
VALLEY WILL GRADUALLY SLIDE EAST TONIGHT. HIGH CLOUDS STREAMING ALOFT
ON A FAST MOVING JET WILL SUBSIDE TONIGHT...LEAVING SKIES MAINLY
CLEAR...AND ALLOWING TEMPERATURES TO BOTTOM OUT SIMILAR TO LAST NIGHT
WITH DEWPOINTS IN THE SINGLE DIGITS. HIGH CLOUDS WILL RETURN TOWARDS
DAWN HOWEVER...AS ANOTHER WEAKER JET STREAK TRANSPORTS MOISTURE.
THE NEXT SYSTEM WILL APPROACH ON SATURDAY AS A LOW LEVEL JET ALONG
WITH AN ACCOMPANYING SHORT WAVE TROUGH TAKE AIM AT THE AREA. THERE IS
STILL SOME QUESTION AS TO WHETHER OR NOT LOCATIONS NORTH OF THE
MOUNTAIN PARKWAY WILL START WITH A BRIEF ONSET OF FROZEN
PRECIPITATION. BASED ON THE LATEST FORECAST SOUNDINGS AND TIME HEIGHTS...
THINK THERE IS A SLIGHT CHANCE OF SLEET AT ONSET...HOWEVER THIS WILL
BE MAINLY A PLAIN RAIN EVENT AND DO NOT FORESEE ANY SIGNIFICANT
IMPACTS.
LIGHT RAIN WILL LINGER INTO SUNDAY...BEFORE TAPERING OFF BY LATE IN
THE DAY AS THE DEEPER MOISTURE EXITS.
FOR TEMPERATURES...STAYING ON THE COOL SIDE FOR THE LOWS AND HIGHS
HAS WORKED WELL AND CONTINUING WITH THIS TREND...ESPECIALLY ON LOWS
TONIGHT AND HIGHS TOMORROW WITH A QUICK INCREASE IN CLOUDS. READINGS
WILL ACTUALLY RISE THROUGH TOMORROW NIGHT AND INTO SUNDAY...WITH NOT
MUCH OF A DROP SUNDAY NIGHT. STUCK CLOSER TO GUIDANCE HERE...ALTHOUGH
DID SHRINK THE DIURNAL RANGE A BIT WITH LINGERING LOW LEVEL CLOUD
COVER.
.LONG TERM.../MONDAY THROUGH FRIDAY/
COLD FRONT TO ARRIVE EARLY TUE. GFS/ECMWF/CANADIAN SHOW FAIR
AGREEMENT ON TIMING AND EACH WITH LESS THAN 0.10 INCH QPF. GFS
HAS MOISTURE NO DEEPER THAN 800 MB BUT UPWARD MOTION IS A LITTLE
BETTER THAN PREVIOUS RUNS AND BETTER COINCIDENT WITH THE MOISTURE
AVAILABLE. SO VERY LIGHT RAIN WITH THIS EVENT LOOKS GOOD BUT KEPT
PROBABILITY AT CHANCE AND MUCH TOO WARM FOR ANY PHASE OTHER THAN
LIQUID PRECIPITATION.
THEREAFTER THE LONGWAVE PATTERN AMPLIFIES FROM THIS FAST ZONAL FLOW
TO TROUGH OVER EAST COAST. GFS ENSEMBLE SHOWS A FAIRLY WIDE SOLUTION
AT THE END OF THE WEEK OVER SNOW POSSIBILITIES AND SOME INDICATE A
LAKE EFFECT SNOW CONNECTION TO LAKE MI. THAT SCENARIO IS A MAJOR
CHANGE FROM 00Z AND 06Z RUNS AND DIFFERENT STILL FROM ECMWF. BUT
SOMETHING TO WATCH.
STUCK CLOSE TO MEX TEMPERATURES THOUGH ENSEMBLE 850 MB STANDARD
DEVIATION BECOMES QUITE LARGE TOWARD THE LATTER HALF OF WEEK...WHICH
JUST HIGHLIGHTS THAT A PATTERN CHANGE IS COMING.
&&
.AVIATION.../00Z TO 24Z/
HIGH PRESSURE WILL CONTINUE TO PROVIDE VFR CONDITIONS AND LIGHT WINDS
THROUGH THE PERIOD. HIGH CLOUDS WILL MOVE INTO THE REGION DURING THE
DAY SATURDAY WITH LOWER CLOUDS ARRIVING LATE IN THE AFTERNOON AHEAD
OF THE NEXT APPROACHING SYSTEM.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...GEOGERIAN/RAY
LONG TERM....GV
AVIATION...GREIF
