Severe Thunderstorm Warning 117, NWS Jackson, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
249 PM EDT THU JUN 12 2008

.SHORT TERM.../TONIGHT THROUGH SATURDAY NIGHT/...UPDATED

THE MAIN ISSUES FOR THE SHORT TERM WILL DEAL WITH DIURNALLY DRIVEN
THUNDERSTORMS TONIGHT AND FRIDAY...THEN THE IMPACT OF A COLD FRONTAL
PASSAGE ON FRIDAY NIGHT/SATURDAY/SATURDAY NIGHT. TODAY...EAST
KENTUCKY HAS BEEN UNDER THE INFLUENCE OF PERSISTENT SOUTHERLY FLOW
BETWEEN RETREATING HIGH PRESSURE AND APPROACHING LOW. MOISTURE RETURN
IS VERY EVIDENT THROUGH OBS AND AN INTERESTING VISIBLE SATELLITE LOOP.
WITH DEWPOINTS BACK IN THE MID TO UPPER 60S AND BETTER THAN DRY
ADIABATIC LAPSE RATES THROUGH A SIGNIFICANT LOW LEVEL DEPTH...VERY
UNSTABLE AIRMASS IS IN PLACE. TOWERING CUMULUS HAVE STARTED TO DEVELOP
...WITH THUNDERSTORMS ALREADY POPPING TO THE SOUTH OF THE CWA. VERY
WEAK WIND SHEAR PROFILES WILL NOT PROMOTE MUCH MOVEMENT WITH STORMS...
SO MOST LIKELY STORMS WE SEE WILL FIRE IN OUR CWA AS CONVECTIVE
TEMPERATURE IS REACHED AND TERRAIN INFLUENCES HELP OUT THE CAUSE OVER
THE NEXT FEW HOURS. HAVE MAINTAINED SLIGHT CHANCE POPS THROUGHOUT THE
ENTIRE CWA FOR MUCH OF THE EVENING. CONSIDERED GOING WITH CHANCE...
BUT FELT SLIGHT CHANCE WOULD BETTER HANDLE THE COVERAGE.

AS WE HEAD INTO FRIDAY...SHOWERS AND THUNDERSTORMS SHOULD FIRE
EARLIER...ESPECIALLY IN THE NORTH AS PREFRONTAL WAVE MOVES INTO THE
AREA. 12Z NAM/GFS SEEM TO HINT AT SOME PREFRONTAL ACTIVITY...SO WILL
GO WITH CHANCE POPS NORTH AND WEST AND SLIGHT CHANCE POPS THE FURTHER
SOUTH AND EAST FROM THE FRONT. FRIDAY NIGHT WILL SEE INCREASING POPS
CWA WIDE AS THE MAIN LINE OF PRECIPITATION ENTERS THE CWA. HAVE
MAINTAINED LOW END LIKELY FOR ALL OF CWA...MAINLY DURING MID MORNING
ON SATURDAY. FORECAST SOUNDINGS SHOW WEAK TO MODERATE INSTABILITY
WITH WIND PROFILES SUFFERING AS WELL. HOWEVER...WITH FORCING FROM THE
FRONT AND MORE SHEAR THAN ANY OF THE PULSE STORMS SEEN OVER THE PAST
COUPLE OF DAYS...A SEVERE STORM OR TWO CANNOT BE RULED OUT. THE STORM
PREDICTION CENTER HAS PLACED THE EASTER PART OF THE CWA IN A SLIGHT
RISK FOR SATURDAY AND WOULD NOT BE SURPRISED TO SEE A SEVERE STORM OR
TWO. PERHAPS THE BIGGER THREAT WITH THESE STORMS WILL BE THE HEAVY
RAIN THREAT AS VERY DEEP MOIST COLUMN...SOMEWHAT SLOWER STORM MOTION
...AND PWATS ABOVE AN INCH AND A HALF SUPPORT HEAVY RAINFALL AT
TIMES. WILL MENTION THESE THREATS IN THE HWO.

WILL KEEP SLIGHT CHANCE POPS ALL THE WAY THROUGH SATURDAY AFTERNOON
AND EVENING AS 12Z NAM SHOWS REDEVELOPMENT RIGHT ON THE FRONT AS IT
PASSES. THE FRONT FINALLY PASSES SATURDAY NIGHT...WITH MUCH DRIER AIR
AND MORE SEASONABLE TEMPERATURES AWAITING BEHIND IT.

DID NOT MAKE MANY CHANGES TO TEMPERATURES AS LATEST GUIDANCE VALUES
SEEMED PRETTY REASONABLE COMPARED TO PREVIOUS FORECASTS. HAVE
INCLUDED PATCHY VALLEY FOG FOR TONIGHT...HOWEVER WITH MORE CLOUD
COVER THAN LAST NIGHT AND STRONGER SURFACE WINDS...EXCEPT IN DEEP
VALLEYS...FOG MAY NOT BE MUCH OF AN ISSUE AT ALL. ZFP WILL BE OUT
SHORTLY.

.LONG TERM.../SUNDAY THROUGH THURSDAY/...UPDATED

THE FOCUS FOR THE BEGINNING OF THE LONG TERM PERIOD WILL DEAL WITH
THE EXIT OF A COLD FRONT AND THE APPROACH OF A SECONDARY FRONT.
SUNDAY SHOULD BE DRY AS HIGH PRESSURE BRIEFLY TAKES OVER BEFORE THE
APPROACH OF A SECONDARY WAVE EMBEDDED IN THE EASTERN CONUS H5
TROUGH. HAVE GONE WITH CHANCE POPS...MAINLY NORTH OF INTERSTATE 64
...WITH SLIGHT CHANCE POPS EVERYWHERE ELSE AS FRONT BEGINS TO WASH
OUT OVER THE AREA. SLIGHT CHANCES FOR PRECIPITATION WILL LINGER
THROUGH MONDAY NIGHT...ESPECIALLY IN THE HIGHER TERRAIN AS UPSLOPE
FLOW BEHIND THE COLD FRONT SHOULD BE ABLE TO USE ANY LINGERING
MOISTURE. THE REST OF THE EXTENDED LOOKS TO BE DRY AND UNEVENTFUL AS
A STRONG HIGH PRESSURE BUILDS IN BEHIND THE COLD FRONT STARTING
TUESDAY.

FORECAST SOUNDINGS FOR THE PASSAGE OF THE COLD FRONT ON MONDAY DO
SHOW WEAK TO MODERATE INSTABILITY WITH PRETTY DESCENT SPEED SHEAR.
THESE INGREDIENTS SHOULD PROVIDE A CHANCE FOR A FEW ORGANIZED
UPDRAFTS. WILL MENTION THUNDERSTORMS IN THE ZFP AND MENTION THE
POSSIBILITY FOR A FEW STRONG STORMS WITH GUSTY WINDS...SMALL
HAIL...AND HEAVY DOWNPOURS.

AS FAR AS THE TIMING OF THE FRONT GOES...GFS SOLUTION HAS COME IN A
LITTLE FASTER. DECIDED TO BLEND BETWEEN ECMWF/GEFS ALONG WITH HPC
THINKING. KEPT TEMPERATURES GENERALLY JUST ABOVE GUIDANCE THROUGHOUT
THE EXTENDED WITH A FEW MINOR TWEAKS HERE AND THERE.

&&

.AVIATION.../18Z TO 18Z/

SCATTERED CONVECTION WILL DEVELOP THROUGH EAST KENTUCKY THIS
AFTERNOON...BUT FOR THE MOST PART THE PREVAILING CONDITIONS AT ALL
THE TAF SITES WILL BE VFR. HAVE CARRIED VCTS AND CB INTO THE EVENING
FOR THESE LOCATIONS...BUT COVERAGE SHOULD BE LIMITED ENOUGH TO
JUSTIFY KEEPING A CIG OR VIS RESTRICTION OUT OF THE TAFS. SHOULD A
THUNDERSTORM MOVE OVER A SITE...MVFR VIS AND CIGS WOULD LIKELY OCCUR
FOR A BRIEF TIME. QUITE WEATHER NIGHT WILL KEEP THE TAFS CLEAN AFTER
02Z...LEAVING ANY BR OUT FOR NOW. THEN ON FRIDAY HAVE INTRODUCED THE
POSSIBILITY OF A VCTS AND CB FOR THE ENTIRE AREA AS THAT FRONT COMES
CLOSER. EXPECT BETTER COVERAGE LATER IN THE DAY THAT WILL LIKELY NEED
PREVAILING RESTRICTIONS IN FUTURE TAF ISSUANCES. WINDS WILL STAY FROM
THE SOUTH AT UP TOWARD 10 KTS DURING THE DAY AND LIGHT AT NIGHT.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...NONE.

&&

SHORT TERM...SCHOETTMER
LONG TERM...SCHOETTMER
AVIATION...GREIF

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