FXUS63 KLMK 031546
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1046 AM EST THU DEC 3 2009
...FORECAST UPDATE...
CLOUD COVER IS ACROSS ENTIRE REGION...BUT CLOUDS ARE NOT THICK
ENOUGH AND DO NOT HAVE ANY MORE SUPPORT TO GENERATE SPRINKLES/RAIN
CHANCES. WILL UPDATE ZONES TO REMOVE SPRINKLE WORDING. EDGE OF
OVERCAST DECK IS GRADUALLY ERODING FROM THE WEST. MAY SEE SOME
BREAKS WITHIN THE DECK AS WELL...AS LATEST VISIBLE SATELLITE IMAGERY
SHOWS SOME THINNER SPOTS OVER THE WESTERN CWA. ASSUMING SOME SUN
WOULD BREAK IN THERE HAVE THE SOUTHWEST ZONES GETTING TO THE LOWER
40S...BUT MOST EVERYONE ELSE SHOULD STAY AROUND 40 FOR HIGHS.
HIGH PRESSURE BUILDING IN FROM THE ROCKIES WILL BRING WESTERLY WINDS
TODAY. EXPECT WIND CHILLS TO PEAK OUT IN THE MID 30S TODAY...SO IT
WILL BE A BRISK EARLY DECEMBER DAY. ZONE UPDATE WITH ABOVE CHANGES
WILL BE OUT SHORTLY.
.SHORT TERM (TODAY AND TONIGHT)...
AT 08Z THE LAST SMALL AREAS OF PRECIPITATION FROM WEDNESDAY/S STORM
SYSTEM WERE PULLING OUT OF THE LMK CWFA...WITH JUST A FEW PATCHES OF
DRIZZLE LEFT. RADARS UPSTREAM HAVE BEEN DRYING UP OVER THE PAST FEW
HOURS. A FEW SPRINKLES OR A PATCH OR TWO OF VERY LIGHT DRIZZLE WILL
BE POSSIBLE EARLY THIS MORNING...BUT FOR THE MOST PART IT LOOKS LIKE
OUR PRECIPITATION IS QUICKLY COMING TO AN END.
LOW LEVEL MOISTURE..GENERALLY AT AND BELOW 5000 FEET...LOOKS TO GET
TRAPPED UNDER AN INVERSION TODAY RESULTING IN CONTINUED WIDESPREAD
CLOUD COVER. THE CLOUDS SHOULD PARTIALLY BREAK UP TONIGHT AS DRIER
AIR MOVES IN ON THE NOSE OF HIGH PRESSURE COMING OUT OF THE PLAINS.
TEMPERATURES WILL BE CHILLY TODAY WITH HIGHS ONLY IN THE LOWER AND
MIDDLE 40S. HOWEVER WITH YESTERDAY/S LOW PRESSURE MOVING AWAY AND A
WEAKER PRESSURE GRADIENT THE WINDS WON/T BE AS STRONG AS THEY WERE
ON WEDNESDAY...WITH SPEEDS OUT OF THE WEST AROUND 10 MPH.
LOW TEMPERATURES TONIGHT WILL BE GREATLY DEPENDENT ON CLOUD
COVER...RIGHT NOW WILL GENERALLY GO WITH MIDDLE 20S WITH A GENTLE
WEST BREEZE.
.LONG TERM (FRIDAY - WEDNESDAY)...
TWO MAIN WEATHER SYSTEMS ARE OF CONCERN IN THE LONG TERM PERIOD.
OVERALL...00Z OPERATIONAL MODELS (GFS...ECMWF...GEM) ARE REASONABLY
SIMILAR THROUGHOUT PERIOD...LENDING SOME CONFIDENCE TO DAY TO DAY
EVOLUTION OF SYSTEMS.
THE FIRST SYSTEM COULD AFFECT OUR SERN FCST AREA LATE FRI NIGHT AND
SAT. MODELS ARE CONSISTENT IN SHOWING THAT A SRN STREAM SHORTWAVE
WILL ROTATE NEWD ON SRN FLANK OF MEAN 500 MB TROF AXIS. THE EXACT
PATH OF THIS SHORTWAVE WILL BE CRUCIAL TO SENSIBLE WEATHER DURING
THIS PERIOD. PRIMARY LOW-LEVEL JET WITH THIS SYSTEM WILL REMAIN SE
OF OUR FCST AREA. HOWEVER...MODELS SUGGEST SOME 850-700 MB
FRONTOGENETICAL FORCING OVER SERN KY...POSSIBLY INCLUDING A FEW OF
OUR SERN COUNTIES IN CNTRL KY. THERE IS ALSO WEAK 700-500 MB
FRONTOGENETICAL FORCING TO THE NW OF THIS AREA SUGGESTING A GOOD MID
DECK OF CLOUDS OVER MUCH OF CNTRL KY FRI NIGHT INTO SAT. FROM AN
UPPER-LEVEL JET PERSPECTIVE...A NICE SRN STREAM W TO E ORIENTED JET
AXIS IS SHOWN OVER THE GULF STATES WITH THE ENTRANCE REGION OF A NRN
STREAM JET OVER THE TN VALLEY. THIS WOULD ENHANCE UPPER-LEVEL
DIVERGENCE AND DEFORMATION OVER THE SRN APPALACHIANS INCLUDING ERN
TN AND INTO SERN KY. TEMPS SHOULD BE COLD ENOUGH FOR FROZEN PRECIP
DURING EVENT. BEST CHANCE OF SNOW WILL BE OVER SERN KY (EAST OF OUR
FCST AREA) WHERE SOME ACCUMULATION IS POSSIBLE. WILL INSERT A
SMALLER CHANCE OF SNOW FOR NOW OVER A TIER OF OUR SERN COUNTIES.
OPERATIONAL MODELS WOULD SUGGEST THAT A CHANCE OF LIGHT SNOW OR AT
LEAST FLURRIES WOULD EXIST FARTHER WEST ACROSS PARTS OF S-CNTRL INTO
E-CNTRL KY. HOWEVER...00Z ENSEMBLES ARE SLIGHTLY FARTHER EAST WITH
PRECIP THAN OPERATIONAL MODELS. AGAIN...PATH OF SHORTWAVE WILL BE A
BIG DETERMINING FACTOR FOR THIS SYSTEM... ALTHOUGH MODELS HAVE BEEN
QUITE CONSISTENT FOR THE LAST FEW MODEL RUNS ON THE PATH OF THE
SYSTEM. FCST WILL BE REFINED AS LATER MODEL AND OBSERVATIONAL
GUIDANCE BECOMES AVAILABLE.
THIS SYSTEM WILL RACE NE OUT OF THE AREA BY SAT AFTERNOON AND
EVENING...LEAVING TRANQUIL WEATHER BEHIND. HIGH TEMPS SAT SHOULD
ONLY BE IN THE LOWER 30S OVER SERN FCST AREA WITH CLOUDS AND CHANCE
OF SNOW. ELSEWHERE...NOT MUCH BETTER...MAX TEMPS ONLY IN MID TO
UPPER 30S.
A SLIGHT MODERATION IN TEMPS OCCURS SUN AND MON WITH HIGHS GETTING
INTO THE 40S IN MOST AREAS. MODELS SUGGEST A WEAK SHORTWAVE PASSING
THROUGH AREA ON SUN NIGHT OR MON...BUT GIVEN UPPER-LEVEL JET
POSITION WITH THIS SYSTEM...ANY PRECIP SHOULD BE CONFINED TO THE
NORTH OF OUR FCST AREA (I.E. NORTH OF THE W TO E ORIENTED JET AXIS
ALOFT).
NEXT SIGNIFICANT WEATHER SYSTEM SHOULD AFFECT OUR AREA TUE AFTERNOON
INTO WED. THIS SYSTEM SHOULD HAVE ENOUGH WARM AIR WITH IT FOR A RAIN
EVENT OVER ENTIRE AREA...ALBEIT A CHILLY RAIN OVER NRN SECTIONS OF
OUR AREA. THIS LOOKS LIKE A DECENT RAIN EVENT AS SURFACE LOW
PRESSURE WORKS NEWD FROM THE SRN PLAINS/LOWER MS VALLEY INTO THE TN
AND LOWER OH VALLEYS. COLDER AIR FOLLOWS PASSAGE OF THE SYSTEM.
&&
.AVIATION (12Z TAF ISSUANCE)...
LOW CLOUDS WILL REMAIN STUBBORN TODAY AS LOW LEVEL MOISTURE
CONTINUES TO SPILL SOUTHWARD INTO THE REGION. WILL HAVE MVFR
CEILINGS IN THE TAFS THROUGH THE DAY AND INTO THE EARLY EVENING
HOURS BEFORE ALLOWING THEM TO BREAK UP AND BE REPLACED BY BROKEN AC.
AS YESTERDAY/S LOW PRESSURE MOVES OFF TO THE NORTHEAST AND HIGH
PRESSURE RIDGES IN FROM THE PLAINS OUR WINDS WILL BE LIGHTER AND
LESS GUSTY TODAY THAN YESTERDAY AND WILL BE CONSISTENTLY OUT OF THE
WEST.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&
$$
UPDATE.........RJS
SHORT TERM.....13
LONG TERM......TWF
AVIATION.......13
