199
FXUS63 KPAH 060924
AFDPAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
424 AM CDT SUN JUL 6 2008
DISCUSSION
AS OF 08Z /2 AM SUNDAY/...THE EFFECTIVE WARM FRONTAL SLOPE IN THE
OVER SWRN HALF OF THE WFO PAH FORECAST AREA. THE SURFACE BOUNDARY
WAS LOCATED ROUGHLY WEST OF A POPLAR BLUFF...PIEDMONT MISSOURI
LINE...THE 925 MB BOUNDARY ORIENTED FROM FULTON KY...NWD TO CAIRO
IL AND PERRYVILLE MO AND THE 850 MB BOUNDARY WAS LOCATED FROM NEAR
FORT CAMPBELL KY TO JUST WEST OF MOUNT VERNON. A SCATTERED TO
BROKEN CUMULUS DECK HAS DEVELOPED WITHIN THIS FRONTAL SLOPE UNDER
WEAK WARM AIR ADVECTION. THE SURFACE DEWPOINT/TEMPERATURE
GRADIENT IS ALSO REFLECTED IN THIS ZONE WITH THE HIGHEST
TEMPERATURES NOTED ALONG THE WESTERN FOOTHILLS OF SOUTHEAST
MISSOURI. FURTHER TO THE EAST...THE INFLUENCE OF THE
NOCTURNAL/SUBSIDENCE INVERSION FROM THE DEPARTING RIDGE IS
SQUASHING ANY EFFECTIVE ISENTROPIC LIFT/MIXING. TO THE SOUTHWEST...
POTENTIAL CONVECTIVE INSTABILITY/MOISTURE IS AVAILABLE AT THE
LOWEST LEVELS SOUTH OF POPLAR BLUFF...BUT THE LACK OF ANY
SIGNIFICANT TRIGGER/BOUNDARY TO LIFT PARCELS IS KEEPING THE
CHANCES FOR PRE-DAWN CONVECTION TO A MINIMUM. HOWEVER...WITH
ANTICIPATED INSOLATION...TEMPERATURES SHOULD RISE QUICKLY ENOUGH
TO SUPPORT ISOLATED TO WIDELY SCATTERED CONVECTIVE ACTIVITY...ESPECIALLY
DURING THE AFTERNOON HOURS OVER SOUTHEASTERN MO...WEST OF A DEXTER
TO MARBLE HILL MISSOURI LINE.
FOR TODAY...THE MOVEMENT OF THE UPPER LEVEL RIDGE SEWD OVER THE
WFO PAH FORECAST AREA SHOULD HELP PROVIDE THE THERMAL CAP TO
INHIBIT EFFECTIVE CONVECTIVE ACTIVITY IN THE AREA. ALSO...GOES
WATER VAPOR SOUNDER IMAGERY SHOWS AN EXTENSIVE DRY SLOT CENTERED
ON THOSE SATELLITE CHANNELS CENTERED NEAR THE 700/850 MB LEVELS.
UNTIL THE MOISTURE ALONG THE WESTERN LIMB/SLOPE OF THE UPPER RIDGE
MOVES OVER THE WFO PAH FORECAST AREA LATER THIS AFTERNOON AND
TONIGHT...THE MOST CONSISTENT MOISTURE POOL WILL BE LIMITED TO
BELOW 850 MB...AND MORE LIKELY AT THE 875-900 MB LEVEL TODAY. THIS
WOULD NOT BE ENOUGH TO SUPPORT SUSTAINED CONVECTION OVER A
WIDESPREAD AREA TODAY. THEREFORE...I HAVE KEPT THE REMAINDER OF
THE WFO PAH FORECAST AREA DRY TODAY.
FOR TONIGHT...SUFFICIENT MOISTURE FOR DEEP CONVECTION...COMBINED
WITH AN APPROACHING SHEARED VORTICITY ZONE ALONG THE WESTERN LIMB
OF THE SW-NEWD TILTED UPPER RIDGE SHOULD MOVE JUST TO THE NORTHERN
EDGE OF THE WFO PAH FORECAST AREA AFTER MIDNIGHT TONIGHT...SETTING
THE STAGE FOR A GLANCING BLOW OF ISOLATED SHOWERS/THUNDERSTORMS
NORTH OF THE INTERSTATE 64 CORRIDOR. FOR THE MOST PART...NONE OF
THE AREA SHOULD SEE ANY ACTIVITY OVERNIGHT. THE 40KM GFS AND SREF
APPEAR TO HAVE THE BEST TIMING AND POSITION OF THE WEATHER
FEATURES DURING THIS TIME PERIOD.
FOR MONDAY AFTERNOON AND EVENING...THE AFOREMENTIONED VORTICITY
ZONE WILL PARK OVER THE WFO PAH FORECAST AREA...AS THE UPPER RIDGE
FLATTENS...BRINGING SLIGHTLY HIGHER SHEAR INTO THE AREA. A LITTLE
MORE/DEEPER MOISTURE WILL BE AVAILABLE...AND WITH GOOD
INSOLATION...ISOLATED TO LOCALLY SCATTERED SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE...ESPECIALLY EAST OF THE
MISSISSIPPI RIVER. THE SREF GUIDANCE WAS GIVEN MORE WEIGHT FOR
POP/WEATHER CHANCES FOR THIS TIME PERIOD.
FOR TUESDAY AND WEDNESDAY...THE RIDGE FLATTENS EVEN
MORE...BECOMING MORE ZONAL WITH THE BASE OF THE WESTERLIES MOVING
CLOSER TO THE WFO PAH FORECAST AREA. ONCE AGAIN...LEANED TOWARD A
BLEND OF THE GFS/SREF WITH SOME INPUT FROM THE ECMWF TO DETERMINE
POP/WEATHER CHANCES ACROSS THE AREA. THE OUTPUT IS SIMILAR TO
PREVIOUS FORECAST PACKAGES...WITH A SLIGHT ENHANCEMENT IN POP
CHANCES AND QPF AMOUNTS OVER THE NRN/CENTRAL SECTIONS OF THE WFO
PAH FORECAST AREA.
SURFACE WIND FORECAST REPRESENTED A BLEND OF SREF/ECMWF
GUIDANCE...WITH THE MAX/MIN TEMPERATURE/DEWPOINTS REPRESENTING A
30 PERCENT BLENDED INFLUENCE FROM THE GRIDDED MOS/GFS/SREF
NUMERICAL GUIDANCE.
NO FORECAST CHANGES WERE MADE BEYOND DAY 4 /WEDNESDAY/ WITH THIS
FORECAST PACKAGE.
AVIATION
SURFACE LOW PRESSURE OVER THE PLAINS WILL RESULT IN LIGHT SOUTHERLY
WINDS DEVELOPING ACROSS THE AREA TODAY AND TONIGHT. INCREASING
SOUTHWEST WINDS OFF THE SURFACE WILL RESULT IN A SCATTERED TO BROKEN
LOW VFR DECK NEAR 5KFT AGL SPREADING NORTH AND EAST EARLY THIS
MORNING AND PERSISTING OVER THE REGION THROUGH THE DAY AND POSSIBLY
TONIGHT.
THERE IS SOME POTENTIAL FOR DENSE FOG OVER THE EVANSVILLE TRI STATE
AREA EARLY THIS MORNING...BEFORE THE 5 KFT DECK AND LIGHT SOUTH
WINDS ARRIVE. THIS COULD IMPACT KOWB AND KEVV TAFS. OTHERWISE VFR
CONDITIONS ARE EXPECTED OVER THE NEXT 24 HOURS.
PAH WATCHES/WARNINGS/ADVISORIES
KY...NONE.
MO...NONE.
IL...NONE.
IN...NONE.
SHORT/LONG TERM....SMITH
AVIATION...DRS
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