Severe Thunderstorm Warning 199, NWS Paducah, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
235 PM CDT SUN SEP 3 2000

EARLY AFTERNOON SURFACE MAP SHOWED WEAK HIGH PRESSURE OVER WESTERN
OHIO...WITH A FRONTAL BOUNDARY WELL TO OUR NORTH ACROSS THE UPPER
MIDWEST INTO THE NORTHERN PLAINS. FEW CLOUDS OVER THE FA...HOWEVER
A NARROW BAND OF WEAK CONVECTION IS AS CLOSE AS SOUTH CENTRAL INDIANA
WHERE APPARENTLY A WEAK SOUTHWARD MOVING BOUNDARY HAS INITIATED THAT
CONVECTION. MAIN FORECAST CHALLENGES INCLUDE WHETHER OR NOT TO INCLUDE
CHANCE OF CONVECTION MONDAY...AND THE DEGREE OF THE ANTICIPATED COOL
DOWN THIS WEEK.

OVERALL...MODELS ARE IN FAIR AGREEMENT WITH THEIR DEPICTIONS OF WHAT
WILL HAPPEN THE NEXT COUPLE OF DAYS. THEY ALL ADVERTISE THAT THE
RIDGE WILL REMAIN FIRMLY CENTERED OVER THE CENTRAL AND SOUTHERN
PLAINS. A LARGE AREA OF HIGH PRESSURE IS FORECAST TO MOVE ACROSS
CANADA INTO SOUTHERN ONTARIO BY TUESDAY. LARGE DISCREPANCIES EXIST
IN NUMERICAL GUIDANCE...AS BOTH THE AVN AND MRF TRY TO INTRODUCE A
SIGNIFICANT COOL DOWN...WHILE 60HR FWC DOES NOT SHOW THIS. CURRENT
THINKING IS THAT THE CANADIAN AIRMASS WITH THIS SYSTEM WILL SPREAD
SOUTHWESTWARD WITH SOME IMPACT...BUT MODIFICATION SHOULD OCCUR AS
THE UPPER LEVEL RIDGE CENTER REMAINS FIRMLY IN PLACE...AND OVERALL
HEIGHTS REMAIN SAME. THUS WILL TREND COOLER IN ZFP BY MIDWEEK...BUT
MAYBE NOT AS COOL AS MRF/AVN AND NATIONAL GUIDANCE. ALSO WITH AN
EXISTING GRADIENT...WIND SHOULD NOT COMPLETELY DIE OFF. WILL HEDGE
TOWARD COMPROMISE MAV NUMBERS. ETA PROBABLY HAS BEST HANDLE ON
MAGNITUDE AND MOVEMENT OF SURFACE FRONTAL FEATURES.

OTHERWISE...FOR TONIGHT...EXPECT A GRADUAL INCREASE IN CLOUDS FROM
THE NORTHWEST. WATER VAPOR SHOWS MOIST PLUME OF PACIFIC ORIGIN STILL
FEEDING IN ACROSS THE DESERT SOUTHWEST U.S. TO THE CENTRAL PLAINS
AND MID MISSISSIPPI VALLEY. SCATTERED CONVECTION CONTINUES ALONG THE
INTERSTATE 70 CORRIDOR. SOME SUPPORT OFFERED UP BY S/WV MOVING ACROSS
NORTH MISSOURI AND SOUTHERN IOWA. SHEARED VORTICITY ALL THE WAY BACK
INTO THE ROCKIES. THINK THE MODELS HAVE BEEN UNDERESTIMATING THE
INFLUENCE OF MOIST PLUME...AND RESULTANT CONVECTION...SO WILL GO AHEAD
AND INTRODUCE SLIGHT CHANCE POP FOR TONIGHT FOR OUR NORTHWEST
COUNTIES AS THE MOIST AXIS SLOWLY SHIFTS SOUTH.

WILL ADD A LOW CHANCE POP (30 PERCENT) OF SHOWERS AND THUNDERSTORMS
FOR LABOR DAY AS WELL. DEEP MOISTURE MAY BE SOMEWHAT LIMITED...BUT BELIEVE
THAT MOIST PLUME THAT CURRENTLY EXTENDS INTO MISSOURI AND ILLINOIS
WILL SHIFT SE. ALSO...ALL MODELS AGREE THAT LIFTED INDICES WILL BE
-4 TO -8 TOMORROW...WITH TOTAL TOTALS EXCEEDING 50...AND 700-500MB LAPSE
RATES FROM 7 TO 8 DEG C...AND NO CAP. WILL NOT TAKE MUCH TO INITIATE SOME
WIDELY SCATTERED TO SCATTERED CONVECTION.

1000-500MB LAYER MOISTURE AXIS TO SHIFT SE OF THE FORECAST AREA
MONDAY EVENING...WHILE THE SURFACE COLD FRONTAL BOUNDARY MOVES SOUTH
ACROSS THE REGION MONDAY NIGHT. SO EXPECT DECREASING CLOUDS EARLY
ON...WITH LITTLE IN THE WAY OF CLOUD COVER THE REST OF THE WORK
WEEK...AS OVERALL MEAN RELATIVE HUMIDITY TO BE RATHER LOW. HIGH
PRESSURE WILL BE EXPANDING ACROSS MUCH OF THE NATION BY THE END OF
THE WEEK.

.PAH...NONE.
NOLES