FXUS63 KJKL 220244 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
937 PM EST MON DEC 21 2009

.SHORT TERM.../THE REST OF TONIGHT/...UPDATED

MADE A FEW ADJUSTMENTS TO THE SKY COVER GRIDS FOR THE OVERNIGHT
PERIOD...AS THE LATEST SATELLITE DATA AND SURFACE OBS BOTH REVEAL AN
AREA OF CLEARING DEVELOPING ALONG AND JUST TO THE NORTH OF THE
TENNESSEE BORDER. AS THE SKIES DOWN THERE CLEAR OVERNIGHT...SOME FOG
COULD FORM...ESPECIALLY IN RIVER VALLEYS AND NEAR LARGE
LAKES...CREEKS...AND STREAMS. WITH THAT IN MIND...ADDED FOG TO THE
FORECAST FOR THE CUMBERLAND RIVER VALLEY...AS IT APPEARS ANY AMOUNT
OF CLEARING THAT DOES TAKE PLACE TONIGHT WILL NOT EXTEND MUCH FURTHER
NORTH THAN THE TWO TIERS OF COUNTIES ALONG AND JUST NORTH OF THE
TENNESSEE BORDER. THE HOURLY TEMPERATURES HAVE BEEN RUNNING A FEW
DEGREES WARMER THAN PREVIOUSLY FORECAST...SO REAL TIME SURFACE DATA
HAS BEEN INGESTED INTO THE FORECAST GRIDS TO ACCOUNT FOR THE LATEST
TRENDS. ALL IN THE OVERNIGHT LOWS COULD END UP A COUPLE OF DEGREES 
WARMER THAN PREVIOUSLY THOUGHT. ALSO...ALL INDICATIONS ARE THAT ANY 
SNOW FLURRIES THAT FALL TONIGHT WILL BE CONFINED TO RIDGETOPS. WITH 
LITTLE IF ANYTHING SHOWING UP IN THE LATEST RADAR TO SUPPORT SNOW 
ACTIVITY...DECIDED TO REMOVE MENTION OF FLURRIES FROM THE FORECAST 
GRIDS AND ZONE TEXT PRODUCT. UPDATED ZONE FORECAST TEXT PRODUCT WILL 
BE ISSUED SHORTLY.

THE PREVIOUS SHORT TERM FORECAST DISCUSSION FOLLOWS...

/TONIGHT THROUGH WEDNESDAY/

NO SIGNIFICANT WX SYSTEMS TO CONTEND WITH DURING THIS PERIOD. THERE
WILL BE ANOTHER FAST MOVING MID/UPPER LEVEL WAVE IN THE NW FLOW ALOFT
TONIGHT...COUPLED WITH WARM AIR ADVECTION BENEATH. THIS WILL BE VERY
SIMILAR TO LAST NIGHT...EXCEPT FOR A LOWER POP. HAVE INCLUDED A
CHANCE OF FLURRIES IN OUR FAR NORTHERN COUNTIES FOR LATE TONIGHT INTO
TUESDAY. 

THINK THAT WE WILL FINALLY SEE CLOUDS BREAK UP ACROSS THE AREA ON
TUESDAY AS DOWNSLOPE FLOW KICKS IN. HOWEVER...WITH THE COLD AND WET
GROUND...AND IN MANY LOCATIONS STILL SNOW COVERED TO START THE
DAY...HAVE GONE WITH MAX TEMPS ON TUESDAY AT OR BELOW THE COLDEST MOS
GUIDANCE.

TUESDAY NIGHT AND WEDNESDAY CLOUDS WILL BE ON THE INCREASE AGAIN IN
ADVANCE OF THE NEXT MAJOR STORM SYSTEM OVER THE CENTRAL CONUS. MODELS
HAVE COME INTO GENERAL AGREEMENT TO HOLD PRECIP OFF TO OUR WEST
THROUGH WEDNESDAY. THE POSSIBLE EXCEPTION IS IN OUR FAR SW...WHERE A
SLIGHT CHANCE WAS USED LATE DAY WEDNESDAY.

.LONG TERM.../WEDNESDAY NIGHT THROUGH MONDAY/

A COMPLEX UPPER LEVER PATTERN KICKS OFF THE LONG TERM PORTION OF THE
FORECAST AS TWO TROUGHS WILL BE DROPPING THROUGH THE ROCKIES WHILE
RIDGING IS SQUEEZED AND AMPLIFIED THROUGH THE OHIO VALLEY. RIGHT OFF
THE BAT THE GFS IS FASTER WITH THE SOUTHERN MOST TROUGH TO OUR WEST
ON WEDNESDAY NIGHT THAN THE ECMWF AND NAM. THIS DIFFERENCE IS EVENED
OUT BY THURSDAY EVENING AS THE TROUGH SPIRALS AND DEEPENS INTO A DEEP
CLOSED LOW NEAR MKC...THOUGH THE GFS HOLDS BACK MORE ENERGY AND
KEEPS IT THE SECOND TROUGH FURTHER TO THE WEST...SINKING IT THROUGH
THE ROCKIES. MEANWHILE IN THE EAST...STRONG RIDGING WILL MOVE EAST TO
THE OTHER SIDE OF THE APPALACHIANS. AT THIS POINT...ANY SEPARATION
BETWEEN THE TROUGHS BLURS AS ONE BIG CLOSED LOW ROLLS NORTH THROUGH
THE MIDDLE AND UPPER MISSISSIPPI VALLEY ON FRIDAY...ONLY SLOWLY
APPROACHING KENTUCKY. BY SATURDAY MORNING THE GFS RETURNS TO ITS
PROGRESSIVE WAYS AND MOVES THE LOW INTO THE GREAT LAKES WHILE THE
ECMWF LINGERS ITS LOW BEHIND THROUGH THE WEEKEND. THESE DIFFERENCES
FURTHER MAGNIFY ON SUNDAY WITH THE DEEP LOW FROM THE ECMWF STILL JUST
ENTERING THE GREAT LAKES WHILE THE GFS HAS ALREADY SPUN ITS OWN NORTH
INTO CENTRAL CANADA. HOWEVER...LINGERING LOWER HEIGHTS THROUGH THE
OHIO VALLEY IN THE GFS WILL MITIGATE SOME OF THE DISCREPANCIES FOR
SENSIBLE WEATHER. MONDAY WILL FEATURE FLAT RIDGING BUILDING ACROSS
THE PLAINS AND INTO THE TENNESSEE VALLEY FROM THE GFS WHILE THE ECMWF
IS STILL SLOWLY CLEARING OUT THE UPPER LOW AND TROUGH OVER THE
REGION. HAVE FOLLOWED THE ECMWF MOST CLOSELY THROUGH FRIDAY BEFORE
SPLITTINGS THE DIFFERENCE WITH THE GFS FOR THE WEEKEND INTO
MONDAY...ALLOWING FOR A BIT MORE PROGRESSIVE A SOLUTION LATER IN THE
PERIOD.

SENSIBLE WEATHER WILL FEATURE A POTENT LOW DEVELOPING AND RACING
NORTH ON THURSDAY...JUST TO OUR WEST...BEFORE QUICKLY FILLING AND
SLOWLY DRIFTING THROUGH THE UPPER MIDWEST...GREAT LAKES...AND
NORTHERN OHIO VALLEY THROUGH THE HOLIDAY WEEKEND. THIS WILL FINALLY
CLEAR OUT ON MONDAY AND ALLOW HIGH PRESSURE TO RETURN TO THE AREA.
THE DEEPENING OF THE SYSTEM WILL HELP TO KEEP ITS FRONTAL STRUCTURE
FROM MOVING INTO EAST KENTUCKY UNTIL LATER THURSDAY...MINIMIZING THE
THREAT OF RAIN UNTIL THURSDAY NIGHT. ONCE THE FRONTS MOVE THROUGH
THAT NIGHT AND INTO FRIDAY...THEY SHOULD MOVE QUICKLY ENOUGH SO THAT
QPF WILL BE LIMITED ACROSS EAST KENTUCKY. AS A RESULT...EVEN WITH THE
MELTING SNOW FROM WEDNESDAY AND THURSDAY...EXPECT THE RIVERS TO BE
ABLE TO CONTAIN THE MELT OFF AND RUN OFF FROM ADDITIONAL RAINFALL.
THURSDAY WILL ALSO BE NOTED FOR ITS GUSTY WINDS AS A TIGHT PRESSURE
GRADIENT WILL PASS OVER THE CWA DURING THE AFTERNOON AND EVENING
HOURS...BUT AT THIS POINT IT LOOKS TO BE A WEAKER SET UP THAN THE
HIGH WINDS WE SAW FROM A SIMILAR STRONG LOW PASSING TO OUR WEST A
COUPLE OF WEEKS AGO.

FOLLOWING A COUPLE OF DAYS OF 50 PLUS TEMPERATURES...COLDER AIR WILL
POUR BACK INTO THE STATE ON WEST WINDS FRIDAY AND SATURDAY. THIS
COLDER AIR WILL COMBINE WITH THE SOMEWHAT LIMITED WRAP AROUND
MOISTURE OF THE SYSTEM...AND VARIOUS UPPER LEVEL IMPULSE SPINNING
AROUND THE TROUGH...TO GENERATE A THREAT OF SNOW SHOWERS THROUGH THE
WEEKEND AND INTO MONDAY. THROUGHOUT THE WAKE OF THE SYSTEM/S COLD
FRONT THE WINDS WILL NEVER QUITE SWITCH AROUND TO A FAVORABLE
POSITION FOR UPSLOPE FLOW SO HAVE MINIMIZED THE ENHANCEMENT OVER OUR
EASTERN RIDGES LETTING THE BULK OF THE SNOW SHOWERS SLOWLY FILTER IN
FROM THE NORTHWEST AS THE STACKED SYSTEM FURTHER OPENS UP AND DRIFTS
BY TO THE NORTH. EVEN THE DEPTH OF THE COLD AIR IN THE WAKE OF THE
SYSTEM LOOKS PALTRY COMPARED TO THE EARLIER MODEL SUGGESTIONS. WITH
THE DISAGREEMENT IN THE MODELS FOR THE UPPER PATTERN ON MONDAY HAVE
CHOSEN TO MINIMIZE THE THREAT OF ANOTHER SOUTHERN SYSTEM DEVELOPING
AND AFFECTING EAST KENTUCKY LATE IN THE FORECAST...AS DEPICTED BY THE
12Z GFS.

FOR TEMPS...STAYED FAIRLY CLOSE TO HPC AND MOS GUIDANCE WITH ONLY
LIMITED TERRAIN BASED ADJUSTMENTS THROUGH THE PERIOD. POP-WISE...
WENT CATEGORICAL ON THURSDAY NIGHT INTO FRIDAY...SIMILAR TO THE MEX
GUIDANCE...THEN UNDERCUT THE MOS NUMBERS INTO MONDAY. 

&&

.AVIATION.../00Z TO 24Z/

LOW CLOUDS REMAIN OVER THE REGION...THOUGH SOME CLEARING HAS TRIED TO
WORK IN FROM THE SW WITH A LITTLE SUCCESS. THE CLEARING HAS MADE IT
LITTLE MORE THAN A FEW MILES NORTH OF THE KY/TN BORDER ALONG AND TO
THE WEST OF INTERSTATE 75. OTHERWISE...MVFR OR VFR CLOUDS JUST ABOVE
THE MVFR/VFR THRESHOLD REMAIN. MODELS INDICATE THAT DRIER AIR AND
SOME SUBSIDENCE ASSOCIATED WITH RIDGING WILL LEAD TO THIS LOW DECK AT
LEAST SCATTERING OUT BETWEEN 3Z AND 8Z OR SO. AT THE SAME TIME MID
AND HIGH CLOUDS IN ADVANCE OF A WEAK MID LEVEL SYSTEM WILL INVADE THE
REGION. AS THESE CLOUDS MOVE INTO THE AREA...AROUND 6Z...THIS MAY
ALSO HELP TO SCATTER OUT THE LOW DECK. IF CLEARING OR PARTIAL
CLEARING OCCURS...MODELS INDICATE THAT SOME BR IS POSSIBLE AS
CURRENT DEWPOINT DEPRESSIONS ARE LOW. OPTED TO GO WITH IFR BR AT JKL
AND MVFR BR AT SME AND LOZ AFTER 5Z TO 6Z AS SUGGESTED BY 18Z MODEL
DATA. ANY FOG WILL LIFT BY AROUND 14Z...WITH JUST VFR EXPECTED THOUGH
A FEW TO SCT LOW CLOUDS COULD REMAIN BELOW A DECK OF HIGH CLOUDS.

&&

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

&&

$$

SHORT TERM...HAL/AR
LONG TERM....GREIF
AVIATION...JP