FXUS63 KPAH 020938
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
338 AM CST WED DEC 2 2009

.DISCUSSION...
THE LONG AWAITED WEATHER SYSTEM FOR THE WEEK IS ON THE VERGE OF
FINALLY IMPACTING THE WFO PAH FORECAST AREA THIS MORNING...AS OF
PRESS TIME. 

THE SHARP 925-850 MB WARM FRONTAL ZONE WAS ALREADY IN PLACE ACROSS
WEST TENNESSEE AT 00Z WEDNESDAY...JUST WAITING FOR SUFFICIENT UPPER
LEVEL FORCING TO EFFICIENTLY SATURATE PARCELS FROM ALOFT DOWNWARD
TO THE SURFACE. OF COURSE...THE APPROACHING DEFORMATION ZONE
MOVING ACROSS ARKANSAS AT THIS TIME /FROM THE UPPER LOW FURTHER
SOUTHWEST INTO TEXAS/ DOES NOT HURT THE CASE FOR EFFICIENT
PRECIPITATION PRODUCTION.

MAIN ADJUSTMENT FOR TODAY...WAS TO INCREASE POP VALUES TO
CATEGORICAL LEVELS BEFORE 12Z ALONG THE TN/KY BORDER...THEN
TRANSLATE THESE HIGH POP VALUES TO THE NORTH/NORTHWEST THROUGHOUT
THE DAY. WITH THE DEFORMATION ZONE EXPECTED TO BE ANCHORED
PRIMARILY OVER SERN MO/SRN IL/SWRN IN...LEANED TOWARD A LONGER
PERIOD OF MODERATE RAINFALL /AND HIGHER PRECIPITATION AMOUNTS/ FOR
TODAY. 

THERE IS A SMALL POTENTIAL FOR ELEVATED CONVECTION OVER TODD AND
POSSIBLY SERN MULHENBERG/CHRISTIAN COUNTIES THIS AFTERNOON AS SOME
OVERTURNING OF THE THETA-E AIR IS POSSIBLE IN THIS AREA. FOR
NOW...I HAVE DECIDED AGAINST MENTIONING THIS POTENTIAL GIVEN THE
EXTREMELY LOW PROBABILITY OF OCCURRENCE.

FOR THIS EVENING...THE UPPER LOW QUICKLY OPENS UP AND THE
DEFORMATION ZONE SHRINKS AS ENERGY/LIFT SHEARS DOWNSTREAM FROM THE
WFO PAH FORECAST AREA. GIVEN THE LOSS OF LIFT AND MOISTURE WITHIN
THE CRITICAL ICE CRYSTAL LAYER...I SIGNIFICANTLY REDUCED POP
CHANCES BETWEEN 9 PM WEDNESDAY TO 6 AM THURSDAY. ALSO...GIVEN THAT
THE BOUNDARY LAYER WILL STILL REMAIN ABOVE FREEZING...LIMITED ANY
MENTION OF A PRECIPITATION MIX TO ISOLATED AREAS. WITH THAT IN
MIND...DROPPED ANY MEASURABLE SNOWFALL AMOUNTS IN THE GRIDS. 

THE NAM-WRF/SREF...AND SECONDARILY THE ECMWF HAD A DECENT HANDLE
ON THIS SYSTEM AND WAS LEANED ON FOR WIND / TEMPERATURE/
DEWPOINT/ CLOUD COVER GRIDDED FORECAST PARAMETERS.

NO ADJUSTMENTS WERE MADE TO THIS PACKAGE BEYOND SUNDAY. 

&&

.AVIATION...
LIGHT TO MODERATE RAINS WILL OVERSPREAD THE ENTIRE AREA IN THE
FIRST 4 HOURS OF THE TAF PERIOD. CEILINGS WILL QUICKLY DROP INTO
THE MVFR CATEGORY AFTER THE RAIN BEGINS. VISIBILITIES THROUGHOUT
THE AREA WILL LIKELY REACH THOSE LEVELS IN THE PERSISTENT RAINFALL
BY 18Z. SOME IFR CEILINGS ARE LIKELY IN THE AFTERNOON AND EARLY
EVENING. HOWEVER...NOTICEABLE IMPROVEMENT WILL OCCUR FROM WEST TO
EAST DURING THE EVENING...AS THE RAIN COMES TO AN END...AND A
COLD...DRY AIR MASS BEGINS TO INFILTRATE THE REGION. CEILINGS MAY
REMAIN ON THE HIGH END OF MVFR...OR POSSIBLY EVEN CLIMB TO VFR
LEVELS OVERNIGHT.

WINDS WILL REMAIN FROM THE EAST NORTHEAST FOR MUCH OF THE DAY. 
HOWEVER...AS THE SURFACE LOW LIFTS NORTHEAST OF THE AREA IN THE LATE 
AFTERNOON...WINDS WILL QUICKLY SHIFT TO THE NORTHWEST AND INCREASE. 
SUSTAINED WINDS 10-14KTS WITH 20-25KTS GUSTS CAN BE EXPECTED FOR THE 
LAST HALF OF THE TAF PERIOD.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
MO...NONE.
IL...NONE.
IN...NONE.
&&

$$

AVIATION/FIRE WEATHER...DRS
SHORT/LONG TERM PUBLIC...SMITH