Severe Thunderstorm Warning 140, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
140 PM CDT SUN AUG 3 1997

FORECAST PROBLEM IS CHANCES OF THUNDERSTORMS THE REMAINDER OF THIS
AFTERNOON INTO THE EARLY EVENING.

17Z SURFACE ANALYSIS DEPICTED A SLOW MOVING COLD FRONT FROM CENTRAL
WISCONSIN INTO SOUTHWEST MINNESOTA.   A VORTICITY CENTER WAS PUSHING
INTO NORTHWEST WISCONSIN...WITH POSSIBLY ANOTHER SMALLER ONE IN
SOUTHEAST MINNESOTA.

THE BIG QUESTION FOR THIS FORECAST PERIOD IS WHAT WILL HAPPEN AS THE
FRONT SLOWLY PUSHES SOUTH AND GETS UPPER LEVEL SUPPORT FROM THE VORT
CENTERS.  12Z NGM/ETA ARE IN RELATIVE AGREEMENT WITH PUSHING THE
STRONGEST UPPER LEVEL DIVERGENCE IN THE 300 MB TO 250 MB LAYER EAST OF
THE ARX FORECAST AREA THIS EVENING. THE FRONT WILL HAVE SOME WEAK
FRONTOGENETIC FORCING WITH IT AS IT PASSES ACROSS SOUTHWEST WISCONSIN
AND NORTHEAST IOWA EARLY THIS EVENING...WHICH IS SUPPORTED IN THE 1000
MB TO 900 MB FN VECTOR CONVEGENCE FIELD.  INSTABILITY WILL CONTINUE TO
INCREASE WITH CAPES PUSHING 2000-3000 J/KG BY 00Z ACROSS NORTHEAST IOWA
AND EXTREME SOUTHWEST WISCONSIN.

THE BOTTOM LINE IS THAT UNTIL THE FRONT MOVES SOUTH OF THE AREA...THERE
ARE STILL CHANCES FOR THUNDERSTORMS. IT APPEARS THAT THE FRONT WILL BE
MOVING FAST ENOUGH TO BE ABLE TO REMOVE THUNDERSTORM CHANCES FROM MOST
OF THE ARX FORECAST AREA BY MID TO LATE EVENING.

A PROBLEM FOR THE OVERNIGHT HOURS WILL BE FOG DEVELOPMENT.  THE
COMBINATION OF THE MOIST GROUND...CLEARING SKIES...AND FAIRLY LIGHT
WINDS COULD SPELL VISIBLITY PROBLEMS DURING THE EARLY MORNING TOMORROW.
PROBABLY DONT NEED TO PUT FOG IN THE ZONES FOR NOW SINCE LIGHT
NORTHWEST FLOW MAY KEEP IT AT BAY...BUT WILL PASS ALONG TO THE NEXT
SHIFT. LOOKING AT TEMPERATURES...NGM AND AVN NUMERICAL GUIDANCE LOOK
REASONABLE.

COORDINATED WITH MKX.

KING