FXUS63 KJKL 150542
AFDJKL
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
1242 AM EST TUE DEC 15 2009
.SHORT TERM.../THE REST OF TONIGHT/
CLOUDS HAVE MOVED IN FOR A LOW OVERCAST. INCREASED CLOUD COVER...
ALTHOUGH THE HIGH CLOUDS WILL BE SCARCE. PCPN SHOULD COME FROM THE
LOW CLOUDS AND WITH SUCH A SHALLOW MOISTURE LAYER... ANY RAIN WILL BE
VERY LIGHT AND THINK THAT DRIZZLE WILL BE THE BEST REPRESENTATION OF
PCPN CHARACTER. ANY MEASUREMENT WILL BE COUNTED IN 1 OR 2 HUNDREDTHS
OF AN INCH. FNT TO SWEEP THRU THE REGION BETWEEN MIDNIGHT AND DAWN
WITH SLOWLY FALLING TEMPS UNTIL THEN AND CONTINUOUSLY FALLING AFTER
FNTL PASSAGE. MOST PCPN WILL FALL POST FNTL PASSAGE. WITH THE WINDS
SWITCHING TO NW AFTER THE FNT... WED HIGH SHOULD BE NEAR TONIGHTS
LOWS. AND THEN FALLING TO THE LOWER 20S BY WED NITE.
THE PREVIOUS SHORT TERM FORECAST DISCUSSION FOLLOWS...
/TONIGHT THROUGH WEDNESDAY NIGHT/
THE LOW CLOUDS HAVE CLEARED OUT ACROSS MOST OF THE AREA OUTSIDE OF
THE NW AND ALONG THE VA BORDER NEAR CUMBERLAND MTN AND BLACK MTN.
MAINLY MID AND HIGH CLOUDS WERE ACROSS THE REMAINDER OF THE REGION.
AT UPPER LEVELS A RATHER ZONAL PATTERN IS IN PLACE WITH RIDGING
CENTERED BETWEEN CENTERED BETWEEN CUBA AND FL AND EXTENDING NORTH
ALONG THE EASTERN SEABOARD. A RATHER BROAD TROUGH WAS OVER MUCH OF
THE CONUS EAST OF THE PACIFIC COAST.
A COUPLE OF SHORTWAVES WILL TRAVERSE THROUGH THE OH VALLEY
TONIGHT...WITH THE FIRST PASSING GENERALLY NORTH OF THE AREA DURING
THE FIRST HALF OF THE NIGHT AND ANOTHER MOVING INTO THE LOWER OH
VALLEY LATER TONIGHT AND EARLY ON TUE. AN AREA OF LOW PRESSURE
ASSOCIATED WITH THIS MORE NORTHERN SHORTWAVE WILL MOVE INTO THE
GREAT LAKES AND THEN NORTHEAST TONIGHT THROUGH WEDNESDAY WITH A
TRAILING SFC COLD FRONT CROSSING THE AREA TONIGHT. THE COLD FRONT
SHOULD NEAR INTERSTATE 65 AROUND 0Z AND CROSS THE CWA BETWEEN 3Z AND
9Z. THERE WILL ACTUALLY BE BETTER MOISTURE ALONG AND BEHIND THE
FRONT AS IS EVIDENT WITH UPSTREAM LOW CLOUDS OVER THE MS VALLEY AND
LOWER OH VALLEY AND MS VALLEY. ALTHOUGH THE MOISTURE IS NOT PROGGED
TO EXTEND MUCH ABOVE 850 MB...IF AT ALL...THE MODELS INDICATE SOME
WEAK TO MODERATE LIFT CENTERED AROUND 6Z TONIGHT. IN FACT...SOME
ISENTROPIC LIFT SHOULD LEAD TO THE RETURN OF CLOUDS IN ADVANCE OF THE
FRONT...AND THEN LIFT ASSOCIATED MORE WITH THE UPPER LEVEL FEATURES
COMBINED WITH LOW LEVEL FLOW THAT WILL BECOME MORE UPSLOPE WITH TIME
AS THE NIGHT PROGRESSES SHOULD LEAD TO AT LEAST AREAS OF DRIZZLE. MOS
POPS WERE AROUND 20 IN MOST AREAS FOR TONIGHT...BUT THE 9Z SREF IS
CLOSER TO 30. OPTED TO GO WITH A 30 PERCENT CHANCE OF MEASURABLE
PRECIP. WITH THE THREAT OF DRIZZLE STARTING NEAR 3Z IN THE
WEST...SPREADING EAST ALONG/BEHIND THE BOUNDARY AND THEN TAPERING OFF
FROM WEST TO EAST LATE TONIGHT INTO EARLY TUE AFTERNOON AS DRIER AIR
WORKS INTO THE REGION COURTESY OF HIGH PRESSURE BUILDING EAST FROM
THE PLAINS STATES.
ALSO AS THE MAIN TROUGH AXIS SHIFTS EAST ON TUE...THE AIR MASS WILL
COOL ALOFT AS WELL AND COLD ADVECTION WILL OCCUR FOR MUCH OF THE
DAY...THOUGH IT WILL BE STRONGER LATE. THIS SHOULD LEAD TO NEAR
STEADY TEMPERATURES FOR MUCH OF THE DAY ON TUE...WITH A
DROP...ESPECIALLY IN THE NORTH LATE IN THE AFTERNOON WITH STRONGER
COLD ADVECTION KICKING IN. LINGERING LOW LEVEL MOISTURE WILL PERSIST
WELL INTO TUE...IF NOT TUE EVENING...ESPECIALLY IN THE EAST. HOWEVER...AS
HEIGHTS RISE AND THE SFC HIGH BUILDS IN...SKIES SHOULD BE EITHER
CLEAR OR CLEAR OUT OVERNIGHT ON TUE NIGHT. ALSO...THE PRESS GRADIENT
WILL INITIALLY KEEP THINGS STIRRING...BUT AS THE HIGH GETS CLOSER LATE
ON TUE NIGHT...WIND WILL DROP OFF AND ALLOW FOR A BIT OF ENHANCE
RADIATIONAL COOLING AND POSSIBLE SMALL RIDGE/VALLEY SPLIT
LATE...ESPECIALLY WESTERN AREAS.
SHORTWAVE RIDGING...SFC HIGH PRESSURE SHIFTING ACROSS THE AREA AND A
CONTINUING MODERATING AIR MASS WILL DOMINATE FOR WED AND WED NIGHT.
THE HEART OF THE COLDEST AIR AT 850 MB SHOULD BE OVER THE REGION ON
TUE NIGHT...WITH THE AIR MASS STARTING TO MODERATE ON WED. EVEN SO...
THE NE AREAS NEAR THE WV BORDER MAY STRUGGLE TO REACH 40 DEGREES ON
WED...WITH HIGHS LIKELY AVERAGING COLDER ON WED AS COMPARED TO WED.
THIS COOL DOWN WILL BE RATHER BRIEF AND THIS PATTERN APPEARS
FAVORABLE FOR AT LEAST A SMALL TO MODERATE RIDGE/VALLEY SPLIT. WITH
DEWPOINTS EXPECTED TO FALL INTO THE 10S BY WED IN MOST AREAS...LOWS
IN EASTERN VALLEY LOCATIONS IN THE TEENS ARE ANTICIPATED FOR WED
NIGHT...WITH LOW TO MID 20S ELSEWHERE.
.LONG TERM.../THURSDAY THROUGH MONDAY/
GFS/ECWMF/CANADIAN MODELS AGREE THAT A STRONG 5H LOW/TROUGH WILL
SWING WESTWARD THEN SOUTH THIS WEEKEND. THEY DIFFER GREATLY ON
TIMING WITH ECMWF BEING FASTEST WHILE CANADIAN HANGS IT UP IN
WESTERN ONTARIO BY SUNDAY MORNING. GFS TAKES THE PRIMARY LOW
WESTWARD TO THE GREAT LAKES...WHICH IS THE MIDDLE GROUND BETWEEN
THE OTHER TWO BUT MAYBE HARDER TO ACCEPT GIVEN ITS WESTERN CONUS
RIDGE ALMOST COMPLETELY EVAPORATES. ALL OF THESE SCENARIOS TURN
EAST KY COLDER WITH A CHANCE OF SNOW THROUGH THE WEEKEND AND INTO
MONDAY. WILL KEEP THE PROBABILITIES OF SNOW THIS PERIOD THE SAME
GIVEN THEY ARE HIGHER THAN NEIGHBORING AREAS. VERY LITTLE ADJUSTMENT
MADE TO TEMPERATURES AND DO NOT AGREE WITH THE WARMER 12Z MEX DATA.
&&
.AVIATION.../06Z TO 06Z/...UPDATED
A COLD FRONTAL BOUNDARY WILL PASS THROUGH EASTERN BETWEEN 6 AND 8Z.
CLOUD BASES WILL FALL BELOW VFR THRESHOLDS...WITH PREDOMINANT MVFR
CONDITIONS EXPECTED FOR A GOOD PORTION OF THE FORECAST PERIOD. THERE
WILL LIKELY BE A WINDOW OF IFR CONDITIONS...WITH SOME DRIZZLE
POSSIBLE THROUGH THE EARLY MORNING HOURS TODAY. WINDS WILL SHIFT TO
THE NORTHWEST BEHIND THE FRONT. THE RESULTING UPSLOPE FLOW WILL
INTERACT WITH LOW LEVEL MOISTURE...ALLOWING A PERSISTENT DECK OF LOW
STRATUS TO FORM AND REMAIN IN PLACE THROUGH 12Z OR SO AT THE TAF
SITES. DRIZZLE WILL CONTINUE TO FALL FROM THE LOWERING CLOUDS
OVERNIGHT...WITH NOTHING MORE THAN A TRACE OF PRECIPITATION AT ANY
GIVEN LOCATION THROUGH SUNRISE. AFTER 12Z THE CLOUDS WILL BREAK UP
QUICKLY IN THE DRY AND COLD AIR BEHIND THE DEPARTED FRONTAL BOUNDARY.
BY 13 OR 14Z SKIES SHOULD BE CLEAR OR MOSTLY CLEAR AT ALL THREE TAF
SITES.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...JP/DUSTY
LONG TERM....GV
AVIATION...AR
