FXUS63 KLMK 151721
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1221 PM EST TUE DEC 15 2009

...AVIATION UPDATE (18Z TAFS)...

...MORNING UPDATE...

UPDATED FORECAST TO REFLECT COLD TEMPERATURES ACROSS SOUTHERN 
INDIANA. ARCTIC AIR CONTINUES TO FILTER SOUTH. TEMPERATURES SHOULD 
FALL A COUPLE OF DEGREES FROM CURRENT LEVELS NEAR THE LAKE 
CUMBERLAND AREA...WITH NEARLY STEADY TEMPERATURES ACROSS SOUTHERN 
INDIANA. HAVE DELAYED CLEARING SOMEWHAT UNTIL LATER THIS AFTERNOON.

.SHORT TERM (TODAY AND TONIGHT)...

CURRENTLY...THE COLD FRONT HAS MOVED THROUGH THE FORECAST AREA AND 
WINDS HAD SHIFTED TO THE NORTHWEST. SOME LOWER CLOUDS WERE ALSO 
MOVING INTO THE REGION AND THEY WILL STICK AROUND AT LEAST THROUGH 
MIDDAY BEFORE CLEARING FROM WEST TO EAST AS HIGH PRESSURE BUILDS 
EASTWARD FROM THE MID MISSISSIPPI VALLEY.

THE CHALLENGE FOR TODAY IS HIGH TEMPS. HIGH WERE ACTUALLY AT 
MIDNIGHT AND TEMPERATURES WILL NOW BEGIN FALLING BEHIND THE FRONT AS 
COLDER AIR FILTERS INTO THE OHIO VALLEY. EXPECT THAT DURING AT LEAST 
THROUGH THE MORNING HOURS TEMPERATURES WILL FLUCTUATE TOO MUCH AND 
WILL REMAIN IN THE UPPER 30S TO LOW 40S BEFORE FALLING OFF IN THE 
AFTERNOON AND THROUGH TUESDAY NIGHT. THEREFORE...EXPECT TEMPERATURES 
TO START IN THE UPPER 30S NORTHWEST TO THE LOW OR MID 40S SOUTHEAST 
AND FALL INTO THE LOW 30S NORTHWEST TO THE UPPER 30S SOUTHEAST BY 6 
PM. 

VERY DRY AIR WILL FIND ITS WAY INTO THE OHIO VALLEY TONIGHT WITH 
DEWPOINTS FALLING INTO THE UPPER TEENS TO LOW 20S AND OVERNIGHT LOW 
TEMPERATURES WILL FALL TO NEAR OVERNIGHT LOW DEWPOINTS. EXPECT LOWS 
FROM THE UPPER TEENS TO MID 20S.

.LONG TERM (WEDNESDAY - MONDAY)...

WED NGT THRU FRI...

A DRY...COLD PERIOD.

OUR CURRENT FCST STRONGLY FAVORS THE NAM MET MOS WITH COLDER TEMPS  
THAN GFS MOS THRU MUCH OF THE PERIOD. THIS LOOKS GOOD BASED ON THE 
POST FRONTAL AMS UPSTREAM AND TRAJECTORIES. 
  
FRI NGT THRU TUE...

A LITTLE MORE CONFIDENCE IN THE FCST FOR THIS PERIOD...AT LEAST 
EARLY...AS MODELS SHOW SOMEWHAT MORE CONTINUITY. HPC LIKES THE 
CANADIAN/EURO COMBO AT LEAST FOR SAT/SUN. THIS LOOKS TO BE A COLD 
PERIOD (TEMPS WELL BELOW NORMAL) WITH SOME LIGHT PRECIPITATION.

BOTH MODELS INDICATE A LNWV TROF APPROACHING AND MOVG THRU OUR FA 
SAT NGT (CANADIAN) AND SUN (EURO) FOLLOWED BY A SERIES OF CLIPPER 
SYSTEMS FOR MON AND TUE. 

AT THE SFC...BOTH MODELS INDICATE THE DEVELOPMENT OF AN INVERTED 
TROF/WEAK LOW ACRS WKY...MOVG ESE INTO EKY/ETN SAT EVE AND INTO THE 
MID ATLANTIC STATES SUN. BASED ON FCST SOUNDINGS AND PLACEMENT OF 
DEEP MOISTURE...SAT LOOKS LIKE THE BEST PERIOD FOR SOME MEASURABLE 
SNOW...THROUGH WITH TEMPS IN THE MID/UPPER 30S...THERE WOULD BE 
SIGNIFICANT MELTING. AT SOME POINT LATE SAT INTO SAT NIGHT...TEMPS 
WOULD LIKELY FALL ENOUGH FOR SOME MINOR ACCUMS AS WE GET ON THE 
BACKSIDE OF THE SYSTEM. THIS COULD END UP BEING AN ADVISORY 
EVENT...THOUGH IT IS 4 DAYS AWAY AND THERE WILL LIKELY BE CHANGES. 
WORST CASE SCENARIO AT THIS TIME IS THE EURO WHICH PAINTS ABOUT A 
1-4 INCH SNOWFALL...WITH LESSER ACCUMS...ACRS OUR FA LATE SAT/SAT 
NIGHT. THE HIGHER TOTALS WOULD BE ACRS OUR NRN FA. 

TEMPS WILL BE COLD ENOUGH OVER THE WEEKEND BUT WILL GET EVEN COLDER 
MON AND TUE AS AFOREMENTIONED SYSTEM PASSES AND WE GO TO NW FLOW 
WITH SUBSEQUENT CLIPPERS. AT THIS POINT...WILL JUST MENTION FLURRIES 
THIS FAR OUT EARLY NEXT WEEK.

&&

.AVIATION (18Z TAF ISSUANCE)...

TIMING OF THE CLEARING LATE THIS AFTERNOON OR EVENING WILL BE THE 
ONLY CONCERN THIS TAF PERIOD. CEILINGS WILL CONTINUE AROUND 1 TO 2 
THOUSAND FEET UNTIL THEN.  CLEARING IS PROGRESSING SOUTHEAST MORE 
SLOWLY THAN EARLIER THOUGHT. BASED ON THE 925MB RH FIELDS OF THE 12Z 
NAM MODEL...WHICH IS CURRENTLY ACCURATE WITH THE CURRENT CLEARING 
LINE...LOW CLOUDS SHOULD CLEAR OUT AT SDF IN THE 20 TO 22Z TIME 
FRAME. AT BWG...EXPECT CLEARING ALSO LATE THIS AFTERNOON AROUND 20 
TO 22Z. CLEARING AT LEXINGTON WILL LIKELY BE LATER TOWARDS 00Z 
WEDNESDAY. ONCE LOW CLOUDS CLEAR EXPECT MOSTLY CLEAR SKIES TONIGHT 
AND WEDNESDAY. 

WINDS WILL CONTINUE THROUGH LATE AFTERNOON FROM THE NORTHWEST AROUND 
10 TO 12 MPH WITH OCCASIONAL GUSTS UP TO 20 MPH. WINDS WILL LESSEN 
TO AROUND 5 MPH AFTER MIDNIGHT...AND BECOME LIGHT AND VARIABLE BY 
WEDNESDAY AFTERNOON.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

UPDATE.........JSD
SHORT TERM.....EES
LONG TERM......AL
AVIATION.......JSD