FXUS63 KJKL 051124
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
624 AM EST SAT DEC 5 2009

.SHORT TERM.../TODAY THROUGH SUNDAY/

THE MAIN FOCUS FOR THE SHORT TERM FORECAST WILL BE TO DEAL WITH LIGHT
SNOW BEGINNING NOW AND LASTING THROUGH MUCH OF THE DAY ON SATURDAY.
CURRENT RADAR IMAGERY SHOWS SOME RETURNS IN THE 20-30 DBZ RANGE ACROSS
THE CWA...HOWEVER NOT REACHING THE GROUND JUST YET. RECENT RADAR
TRENDS COMBINED WITH VWP DO SUGGEST THAT COLUMN IS STEADILY
SATURATING DOWN AND EXPECT LIGHT SNOW TO BEGIN TO FALL IN MANY
LOCATIONS BY 3 AM. HAVE DECIDED TO EXTEND THE WINTER WEATHER
ADVISORY A LITTLE FURTHER WESTWARD TO ACCOUNT FOR H85-H5
FRONTOGENESIS DEPICTED BY 0Z NAM. WILL NOW INCLUDE WHITLEY...KNOX AND
CLAY COUNTIES TO THE WSW. THIS MATCHES 21Z SREF QPF BAND FURTHER
WEST. FEEL THAT THE 1 TO...LOCALLY 2...INCH LINE WILL BE POSSIBLE
ALONG A LINE FROM WHITLEY COUNTY NORTHWESTWARD TO MARTIN COUNTY AS A
RESULT. EXTENDED THE LIKELY POPS JUST A LITTLE BEST TO MATCH UP WITH
INCREASING SNOW TOTALS TO THE WEST A BIT.

H5 TROUGH AXIS SLIDES BY THE CWA AROUND 18Z TODAY...AND WITH
STEEPENING LAPSE RATES FROM MID LEVEL CAA...FEEL THAT SNOW GETS A BIT
SHOWERY. WITH HIGH PRESSURE BUILDING IN FROM THE WEST...THIS PERIOD
WILL NOT LAST LONG AS LOW LEVEL MOISTURE QUICKLY DIMINISHES AND
CLEARING COMMENCES. TOMORROW NIGHT IS SETTING UP TO BE QUITE CHILLY
AND HAVE LOWERED TEMPERATURES JUST A BIT. FEEL THAT SOME UPPER TEENS
ARE WARRANTED WITH OTHER LOCATIONS IN THE LOWER 20S. TEMPERATURES
THIS COLD WILL BE DEPENDENT ON AMPLE CLEARING. IF FRESH SNOW COVER
DOES NOT MELT OFF IT COULD HELP MORE LOCATIONS INTO THE UPPER TEENS.

TEMPERATURES RECOVER TO THE MID 40S ON SUNDAY WITH MOSTLY CLEAR SKIES
IN ORDER. SOME UPPER LEVEL CLOUDS WILL BEGIN TO ADVECT INTO THE
REGION ON SUNDAY AFTERNOON.

AN UPDATED LONG TERM DISCUSSION WILL FOLLOW SHORTLY.

.LONG TERM.../SUNDAY NIGHT THROUGH FRIDAY/

NO MAJOR CHANGES WERE NECESSARY AS FAR AS TIMING OF SYSTEMS THROUGH
MIDWEEK NOR HAS THE THREAT FOR GUSTY WINDS AT MIDWEEK CHANGED
EITHER. RECENT GUIDANCE HAS COME IN A LITTLE COLDER FOR SUNDAY
NIGHT...SO OPTED TO LOWER VALLEY TEMPERATURES A BIT...ESPECIALLY IN
THE EAST AS THE INITIAL CLOUD COVER IN ADVANCE OF A WEAK SYSTEM LATE
SUNDAY NIGHT AND MONDAY SHOULD BE HIGH CLOUDS TO START THE
NIGHT...WITH SOME MID CLOUDS LATE IN THE NIGHT. MODELS DO NOT
FORECAST THE LOWEST LEVELS TO BECOME MOIST ENOUGH FOR POSSIBLE PRECIP
UNTIL DURING THE DAY ON MONDAY. THERE STILL APPEARS TO BE SOME CHANCE
THAT THE INITIAL PRECIP FROM THIS SYSTEM COULD MIX WITH SNOW IF ICE
CRYSTALS ARE PRESENT AND THE ATMOSPHERE MOISTENS UP ENOUGH WHEN OR IF
THEY ARE PRESENT. A RATHER POTENT AREA OF HIGH PRESSURE IS EXPECTED
TO BRIEFLY BUILD INTO THE AREA BETWEEN THIS SYSTEM AND THE MIDWEEK
SYSTEM. THIS COULD LEAD TO AT LEAST SOME BRIEF CLEARING BETWEEN
SYSTEMS ON MONDAY NIGHT...BUT CONFIDENCE IN THIS IS NOT ALL THAT
HIGH. IF THERE IS AT LEAST A BRIEF PERIOD OF CLEARING AT LEAST A
SMALL RIDGE/VALLEY TEMPERATURE SPLIT COULD OCCUR.

THE MOST RECENT GFS AND ECMWF SUGGEST THAT CLOUDS WILL THICKEN AND
LOWER DURING THE DAY ON TUESDAY AND DEPENDING ON HOW FAST THEY COME
IN...HIGHS SHOULD BE SUPPRESSED TO A FEW TO SEVERAL DEGREES BELOW
MOS...THOUGH SOME AREAS IN THE SOUTHEAST MAY EXPERIENCE SOME
DOWNSLOPE DRYING AND WARMING. OPTED TO LOWER MAX T A FEW AREAS...
ESPECIALLY THE NORTHEAST. PRECIPITATION SHOULD BEGIN TO OVERSPREAD
THE REGION DURING THE AFTERNOON OR EARLY EVENING ON TUESDAY. THE
TIMING OF THIS SYSTEM REMAINS RATHER CONSISTENT FROM MODEL RUN TO
MODEL RUN AND MODEL TO MODEL...AND OPTED TO INCREASE POPS TO CAT IN
THE WESTERN TIER FOR TUE NIGHT AS WELL TO LIKELY IN ALL AREAS FOR TUE
NIGHT. THE THREAT FOR GUSTY WINDS WITH THE MIDWEEK SYSTEM REMAINS
BOTH PRE AND POSTFRONTAL. HOWEVER...THE HIGHER MOMENTUM ALOFT COULD
BE MIXED DOWN IN A MORE WIDESPREAD FASHION WITHIN THE DRY SLOT BEHIND
THE FRONT ON WED. WIND GUSTS ABOVE 40 MPH ARE DEFINITELY NOT OUT OF
THE QUESTION...BUT CONFIDENCE IN EXACT TIMING AND STRENGTH OF THE
SYSTEM AND/OR ANY DRY SLOT WILL PLAY A LARGE ROLE IN THE EVENTUAL
GUST MAGNITUDES.

THE PREVIOUS EXTENDED DISCUSSION FOLLOWS:

04/00Z AND 12Z MODELS OFFER NO BIG SURPRISES SYNOPTICALLY NEXT WEEK
AND FEW CHANGES HAVE BEEN MADE TO THE FORECAST DURING THE PERIOD.
04/00Z ECMWF IS THE PREFERRED MODEL WHERE ANY DIFFERENCES EXIST. THE
DEGREE OF COOLING BEHIND OUR MIDWEEK SYSTEM IS THE BIGGEST QUESTION
MARK... WITH THE GFS BEING 6 TO 7C DEGREES COOLER AT 850 MB THAN THE
ECMWF AT 12Z THURSDAY. THE FAST PROGRESSIVE FLOW SHOULD MEAN LESS
OVERALL INTRUSION OF COLDER AIR THIS FAR SOUTH...THUS THE PREFERENCE
FOR THE WARMER ECMWF.

AS FOR SENSIBLE WEATHER... A WEAK SYSTEM IS STILL ON TAP TO BRING A
THREAT FOR PRECIP TO OUR AREA ON MONDAY. ANTECEDENT CONDITIONS ARE
VERY DRY AND THERE IS NOT A LOT OF MOISTURE ASSOCIATED WITH THE
SYSTEM SO CONTINUED TO ONLY OFFER A SLIGHT CHANCE OF SHOWERS DURING
THE DAY. THICKNESSES UP NORTH INDICATE THE POTENTIAL FOR A LITTLE
SNOW TO MIX IN... IF ANYTHING OCCURS AT ALL. OTHERWISE... A BRIEF
LULL IN RAIN CHANCES MONDAY NIGHT WILL BE FOLLOWED BY CHANCE POPS ON
TUESDAY AS OUR NEXT... MUCH MORE ROBUST SYSTEM APPROACHES FROM THE
WEST. PROGS INDICATE A VERY POTENT LOW LEVEL JET WITH THIS SYSTEM...
WITH GUSTY SOUTH TO SOUTHEASTERLY WINDS AT THE SURFACE. IN FACT...
WINDS MAY BE THE BIGGEST THREAT WITH THIS SYSTEM. A RESULTING RAIN
SHADOW SHOULD MEAN A DELAYED ONSET TO THE PRECIP... HOWEVER...
DYNAMICS WILL LIKELY OVERCOME THIS AND WE INCREASED POPS INTO THE
LIKELY RANGE FOR TUESDAY NIGHT. PROGS INDICATE A SLIGHTLY MORE
PROGRESSIVE SYSTEM SO DROPPED POPS BEHIND THE FRONT ON WEDNESDAY BUT
THERE REMAINS A CHANCE OF RAIN SHOWERS THROUGH THE DAY WITH WRAP
AROUND MOISTURE AFFECTING THE AREA AS THE UPPER TROUGH PASSES BY TO
OUR NORTHWEST. ANY LINGERING RAIN WILL MIX WITH AND CHANGE TO SNOW
WEDNESDAY NIGHT... BUT ANY PRECIP SHOULD BE VERY LIGHT BY THAT TIME.
HIGH PRESSURE WILL THEN SLIDE ACROSS THE OHIO VALLEY LEAVING DRY
CONDITIONS THURSDAY AND THURSDAY NIGHT BUT PROGS ARE ADAMANT THAT
ANOTHER SYSTEM WILL THREATEN THE AREA BY FRIDAY IN THE PROGRESSIVE
FLOW ALOFT SO WILL BRING IN FRIDAY WITH A 20 PERCENT CHANCE OF
SHOWERS.

THE 04/12Z GFSX GUIDANCE TEMPS SEEM VERY REASONABLE WITH THE
EXPECTED PATTERN NEXT WEEK... EVEN FOR TEMPS ON THURSDAY WHERE THE
MOST UNCERTAINTY LIES. THE GUIDANCE AGREES WELL WITH THE INHERITED
FORECAST NUMBERS TOO SO MADE FEW CHANGES OVERALL.

&&

.AVIATION.../12Z TO 12Z/...UPDATED

LIGHT TO...AT TIMES...MODERATE SNOWFALL WILL CONTINUE THIS MORNING
WITH TAF SITES WAFFLING FROM FROM PREDOMINANTLY MVFR TO IFR CIGS/VIS
IN STRONGER SNOW BANDS. VLIFR CANNOT BE RULED OUT IN THE HEAVIEST
SNOW BANDS...HOWEVER THESE CONDITIONS WILL BE SHORT LIVED. EXPECT
THINGS TO TAPER FROM WEST TO EAST BY MID MORNING...WITH KJKL AND
AREAS EAST HANGING ON TO LIGHT SNOW THEN SNOW SHOWERS THE LONGEST.
SOME LIGHT SNOW ACCUMULATION WILL BE POSSIBLE ON RUNWAYS.

HIGH PRESSURE WILL BUILD IN FROM THE WEST LATE THIS AFTERNOON AND
SHOULD ALLOW FOR CLEARING SKIES. HAVE ALL TAF SITES BACK TO VFR BY
THIS AFTERNOON. SURFACE WINDS SHOULD REMAIN MAINLY OUT OF THE NORTH
THROUGH THIS AFTERNOON...THEN VEERING TO EASTERLY OVERNIGHT.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR 
KYZ085>088-110-113-115>120.

&&

$$

SHORT TERM...SCHOETTMER 
LONG TERM....JP 
AVIATION...SCHOETTMER