Severe Thunderstorm Warning 173, NWS Jackson, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
120 PM EDT WED AUG 9 2000

MODELS INDICATE THAT RIDGE OVER ROCKY MOUNTAINS WILL EXPAND NORTHWARD
WHILE A POSITIVELY TILTED TROUGH DEVELOPS IN THE EAST. THIS WILL
RESULT IN AN INCREASINGLY AMPLIFIED FLOW THROUGH FRIDAY. TROUGH AXIS
WILL MOVE EAST OF THE FORECAST AREA BY FRIDAY.

MAIN FORECAST CHALLENGE WILL BE FLASH FLOOD POTENTIAL FOR THE FIRST
PERIOD. FFA IS CURRENTLY IN EFFECTIVE FOR TONIGHT. BASED ON QPF
PROJECTIONS BY ETA/MESOETA...AM INCLINED TO CONTINUE THE FFA. HIGHEST
QPFS ARE DEPICTED IN THE WESTERN PORTION OF THE FORECAST AREA IN
ASSOCIATION WITH A SOUTHBOUND MCS OVERNIGHT. HOWEVER AM NOT CONFIDENT
ENOUGH IN EXACT PLACEMENT OF THIS MCS TO BREAK EASTERN COUNTIES OUT
OF FFA.

MODEL TIME SECTIONS DEPICT A GENERAL DRYING TREND ABOVE THE BOUNDARY
LAYER ON THURSDAY. ETA/MESOETA BRINGS FRONT THROUGH AROUND 18Z
THURSDAY WHILE NGM/AVN ARE 8 TO 10 HOURS EARLIER. WILL OPT TO
CONTINUE SMALL POP FOR MAINLY EARLY PRECIP IN THE SECOND PERIOD.
SURFACE HIGH PRESSURE WILL BUILD INTO AREA BY LATE THURSDAY. AM
CONCERNED THAT ENOUGH BOUNDARY LAYER MOISTURE WILL REMAIN THROUGH
THE FOURTH PERIOD THAT WIDELY SCATTERED AFTERNOON SHOWERS CAN NOT
BE TOTALLY RULED OUT BUT WILL LEAVE OUT MENTION AT THIS TIME.

SLIGHTLY COOLER AIR WILL SUCCEED THE FRONT. THE NORTHERLY SURFACE
FLOW WILL ALSO PROVIDE DRIER AIR AS DEWPOINTS ARE PROJECTED TO
FALL INTO THE LOWER 60S BY FRIDAY. FWC AND AVN MOS GUIDANCE NUMBERS
ARE IN FAIRLY GOOD AGREEMENT WITH AVN SLIGHTLY COOLER THAT FWC.
WILL TEND TO SPLIT THE DIFFERENCE BETWEEN THE TWO.

EXTENDED...MEDIUM RANGE MODELS ARE IN REASONABLY GOOD AGREEMENT
THROUGH THE EXTENDED PERIOD. SOME TIMING DIFFERENCES ARE NOTED AS
MRF IS SOMEWHAT MORE PROGRESSIVE THAN THE OTHER MODELS. ECMWF
MAINTAINS EAST COAST TROUGH LONGER. UPPER RIDGE WILL BUILD EASTWARD
THROUGH THE PERIOD MOVING THE STORM TRACK AROUND THE PERIPHERY OF
THE UPPER RIDGE NORTH AND EAST OF THE FORECAST AREA. HIGH PRESSURE
WILL DOMINATE AT THE SURFACE. WILL MAINTAIN DRY TREND. TEMPS WILL
CLIMB FROM SLIGHTLY BELOW CLIMATOLOGY EARLY IN THE EXTENDED PERIOD
TO ABOVE CLIMATOLOGY BY LATE IN THE PERIOD.

PRELIMINARY CCF FOR COORDINATION PURPOSES. WORK ZONES OUT SHORTLY.

LOZ BB 071/089 064/085 060 2352-
JKL BB 071/087 064/083 061 2351-

.JKL...FFA ALL AREAS THROUGH TONIGHT.

LCM