Severe Thunderstorm Warning 68, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
220 PM CDT THU JUL 8 1999

FORECAST CONCERNS CENTER ON SEVERE WEATHER THREAT TONIGHT AND
INFLUENCE OF UPPER LOW OVER WESTERN GREAT LAKES TOMORROW.

KEEPING A CLOSE EYE ON MESOSCALE FEATURES THIS AFTERNOON WITH
OUTFLOW FROM EARLIER MCS MASKING EXACT POSITION OF WARM FRONT.
LOW LEVEL SHEAR AND HELICITY VALUES OFF OF LAPS SOUNDINGS CONTINUE
TO INCREASE IN VICINITY OF BOUNDARY FROM NORTHEAST IOWA INTO
SOUTHWEST WISCONSIN. CAPES NOT OVERLY IMPRESSIVE YET BECAUSE OF
LIMITED HEATING. THIS MAY DELAY ONSET OF CONVECTION UNTIL LATER
THIS EVENING...FIRST DEVELOPING AS POSSIBLE SUPERCELLS ALONG WARM
FRONT/OUTFLOW...AND THEN AS A LINE WHEN COLD FRONT APPROACHES
TOWARD 06Z.

SLIGHT TIMING DIFFERENCES IN SHORT TERM MODELS...BUT WILL FOLLOW
PERSISTENCE AND ETA/NGM COMBINATION WITH UPPER LOW AND BEST DYNAMICS
MOVING INTO MINNESOTA BY 12Z FRIDAY. SURFACE FRONT STILL PROGGED TO
PUSH THROUGH FORECAST AREA BETWEEN 04Z-08Z. WILL KEEP SEVERE WORDING
FOR THE EVENING HOURS ONLY EXCEPT IN FAR SOUTHEAST ZONES.

LOOKING UPSTREAM...AIR BEHIND FRONT IS CONSIDERABLY DRIER AND COOLER.
WITH UPPER LOW VICINITY WESTERN GREAT LAKES TOMORROW...BREEZY DAY IS
ON TAP...ESPECIALLY WEST OF MISSISSIPPI RIVER WHERE BEST MIXING WILL
OCCUR. COLDER AIR ALOFT AND STEEPER LAPSE RATES MAY KEEP MORE CLOUDS
AROUND AND EVEN DIURNAL SHOWERS CLOSER TO LOW SO OPTED FOR SMALL POPS
OVER NORTHERN AND EASTERN ZONES IN 2ND PERIOD.

BEYOND THAT BROAD RIDGE OVER WESTERN U.S. WILL AMPLIFY ONCE AGAIN
WITH COOL AND QUIET WEATHER HEADING INTO THE WEEKEND. SHORT WAVE
TROUGH ENERGY BY MONDAY MAY BRING NEXT SHOT AT RAIN.

.LSE...NONE.

SHEA