FXUS63 KLMK 041600
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1100 AM EST FRI DEC 4 2009
...FORECAST UPDATE...
SKIES RANGE FROM MOSTLY SUNNY OVER THE NORTHEAST THIRD OF THE CWA TO
MOSTLY CLOUDY ACROSS THE SOUTHEAST. THE CLOUDS ARE STREAMING
NORTHEAST IN THE MOIST UPPER LEVEL FLOW EAST OF A TROUGH RUNNING
FROM THE UPPER MS RIVER VALLEY INTO THE SOUTHERN PLAINS. EXPECT THE
BOUNDARY FOR THE CLOUDS TO REMAIN IN ROUGHLY THE SAME PLACE THROUGH
THE DAY.
EVEN WITH THE SUNSHINE TEMPERATURES HAVE BEEN SLOW TO WARM...BECAUSE
OF THE LOW SUN ANGLE AS WELL AS CHILLY 1000-850 MB THICKNESSES
ACROSS REGION. HAVE SLIGHTLY TWEAKED TEMPERATURES...BUT IN GENERAL
THE CHANGES WILL NOT BE NOTICEABLE IN THE ZONE UPDATE.
.SHORT TERM (TODAY THROUGH SATURDAY)...
THE MAIN CHALLENGE IN THE SHORT TERM IS THE POSSIBILITY OF ANY SNOW
EARLY SATURDAY MORNING IN THE FAR SOUTHEAST.
AT THE SURFACE HIGH PRESSURE WILL RIDGE FROM TEXAS TO NEW ENGLAND
TODAY INTO TOMORROW. LOW PRESSURE WILL BE TRYING TO ORGANIZE OVER
THE GULF AND WILL THEN BEGIN TO DEEPEN AS IT MOVES INTO THE ATLANTIC
OFF THE SOUTHEAST UNITED STATES COAST. AS IT STRENGTHENS IT WILL
FORM A WEAKNESS IN THE RIDGE OVER THE CENTRAL AND SOUTHERN
APPALACHIANS. MEANWHILE...A SHORTWAVE TROF ALOFT WILL BE DIGGING
INTO THE MEAN UPPER TROF AND WILL PASS OVERHEAD EARLY SATURDAY
MORNING.
THE MODELS...TO VARYING DEGREES...BRING PRECIPITATION INTO THE
APPALACHIANS LATE FRIDAY NIGHT INTO SATURDAY MORNING. HOW MUCH MAKES
IT INTO THE LMK CWFA IS UP FOR SOME DEBATE. THERE WILL BE A SHARP
CUT-OFF OF THE SNOW AND CLOUD COVER ON THE NORTHWEST EDGE AND WHERE
THIS CUT-OFF SETS UP WILL DETERMINE WHO SEES SNOWFLAKES AND WHO DOES
NOT. IT ALSO IS VERY IMPORTANT HOW MUCH THE DRY AIR IN THE
850HPA-700HPA LAYER THAT WILL BE IN PLACE AT THE ONSET OF THE EVENT
CAN BE MOISTENED TO ALLOW ANY SNOW TO REACH THE SURFACE.
THE 00Z MESOETA BROUGHT QPF INTO THE LMK CWFA A COUPLE OF COUNTIES
DEEP. QUICK PEEK AT THE 06Z RUN SHOWS IT HAS BACKED OFF ON
PRECIP...KEEPING THE LMK CWFA DRY WITH THE EXCEPTION OF CLINTON
COUNTY AND RIGHT ALONG THE JKL CWFA BORDER. THIS IS A TREND TOWARD
THE 00Z GFS SOLUTION WHICH KEEPS THE LMK CWFA COMPLETELY SNOW FREE.
FOR THESE REASONS WILL KEEP MEASURABLE SNOW POSSIBILITIES IN THE LOW
CHANCE CATEGORY AND RESTRICTED TO THE SOUTHEAST CORNER OF THE LMK
CWFA. BY FAR THE BEST CHANCE FOR ANY ACCUMULATING SNOW WILL BE IN
CLINTON AND RUSSELL COUNTIES...THOUGH EVEN THERE ANY ACCUMULATION
WILL BE ON THE ORDER OF A FEW TENTHS OF AN INCH AT BEST. RIGHT NOW
TIMING APPEARS TO BE BETWEEN 4AM AND 9AM CST.
THE UPPER WAVE AND ASSOCIATED MOISTURE WILL PULL OFF TO THE
NORTHEAST QUITE RAPIDLY AND BY AFTERNOON THE ENTIRE CWFA WILL BE
SEEING SUNSHINE. ANY DUSTING OF SNOW IN THE SOUTHEAST WILL BE LONG
GONE BY EVENING AFTER HIGHS IN THE UPPER 30S AND PLENTY OF AFTERNOON
SUN.
.LONG TERM (SATURDAY NIGHT - THURSDAY)...
SATURDAY NIGHT - MONDAY...
WE/LL START OUT THE LONG TERM SATURDAY NIGHT WITH HIGH PRESSURE
CENTERED TO OUR EAST OVER THE VIRGINIAS AND EASTERN KY. WITH CLEAR
SKIES AND H85 TEMPS IN THE -3 TO -5 DEGREES C RANGE...WE SHOULD SEE
A PRETTY COLD NIGHT IN THE LOWER 20S FOR LOWS. HOWEVER...WITH
PLENTY OF SUNSHINE ON SUNDAY AFTERNOON AND RETURN FLOW...WE WILL
REBOUND INTO THE LOW TO MID 40S FOR HIGHS.
SUNDAY NIGHT WE/LL SEE THE FIRST SYSTEM OF THE LONG TERM PERIOD...A
QUICK MOVING WEAK SFC LOW AND ASSOCIATED UPPER WAVE. THIS SYSTEM
WILL DRAG A WEAK COLD FRONT OVER THE AREA AND PROVIDE US WITH LIGHT
PRECIP. IT LOOKS QUITE POSSIBLE THAT MOST OF THE AREA SHOULD SEE A
RAIN/SNOW MIX SUNDAY NIGHT AFTER MIDNIGHT...EXCEPT FOR SOUTH
CENTRAL KENTUCKY WHICH WILL SEE ONLY RAIN. THERE COULD BE A FEW
SLICK SPOTS MONDAY MORNING ESPECIALLY OVER SOUTHERN INDIANA WHERE
AIR TEMPS LOOK TO DROP BELOW FREEZING. THE LIGHT PRECIP SHOULD BE
OUT OF THE AREA BY EARLY MONDAY AFTERNOON. MONDAY/S HIGH TEMPS LOOK
TO HOLD IN THE LOW TO MID 40S.
TUESDAY - THURSDAY...
A WEATHER SYSTEM OF GREATER STRENGTH LOOKS TO AFFECT THE AREA
TUES-WED. OVERALL IT LOOKS LIKE THIS SYSTEM WILL BE MOSTLY A RAIN
MAKER WITH UP TO AN INCH OF RAIN POSSIBLE IN SPOTS WITH MOST OF IT
FALLING ON TUES NIGHT/EARLY WED. AS THE SYSTEM MOVES OUT AND COLD
AIR DIVES DOWN BEHIND IT...PRECIP COULD END AS SOME LIGHT SNOW
SHOWERS OR FLURRIES ON WED NIGHT. HAVE NOT MADE A WHOLE LOT OF
CHANGES WITH THE FORECAST ON THIS SYSTEM. 0Z GFS/ECMWF AND 12Z GEM
ALL TRENDED SLOWER IN REGARDS TO PRECIP ARRIVAL ON TUESDAY SO HAVE
CUT BACK POPS TO 20% DURING THE MORNING HOURS. ALSO DUE TO THE
LATER ARRIVAL OF PRECIP...HAVE MADE THE PRECIP TYPE AT ONSET PLAIN
RAIN. HAVE NOT CHANGED ANYTHING ON THE BACK SIDE OF THIS
SYSTEM...BUT COULD SEE PRECIP ENDING MORE LIKE WED LATE
AFTERNOON/EARLY EVENING AS OPPOSED TO LATER WED NIGHT BASED ON THE
FASTER TIMING OF THE 0Z MODELS AND ENSEMBLES. HIGH TEMPERATURES
TUES/WED SHOULD STAY IN THE UPPER 30S TO MID 40S...WITH LOWS IN THE
UPPER 20S TO UPPER 30S.
PRELIMINARY FORECASTS SHOW THURSDAY LOOKS COLD AND DRY WITH HIGHS IN
THE 30S AND LOWS IN THE 20S. HOWEVER...0Z GFS OP AND ENSEMBLES SHOW
ANOMALOUSLY COLD AIR FOR THURS SO TEMPS COULD BE COLDER THAN
CURRENTLY FORECAST.
&&
.AVIATION (12Z TAF ISSUANCE)...
QUIET WEATHER IN THE TAFS WITH HIGH PRESSURE IN CONTROL. SCT-BKN AC
STREAMING UP FROM THE SOUTHWEST SHOULD BE ABOUT THE ONLY CLOUD TYPE.
WINDS WILL BE FROM THE WEST AND NORTHWEST TODAY...SHIFTING TO THE
NORTHWEST AND NORTH TONIGHT AROUND 4 TO 7 KNOTS.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&
$$
UPDATE.........RJS
SHORT TERM.....13
LONG TERM......AML
AVIATION.......13
