Severe Thunderstorm Warning 109, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
330 PM CDT SAT AUG 3 2002

FORECAST PROBLEMS ARE CONVECTIVE DEVELOPMENT/SEVERE WEATHER
POTENTIAL  TONIGHT...BOUNDARY LOCATION AND SUBSEQUENT
TEMPERATURE/PRECIPITATION FORECASTS FOR THE REMAINDER OF THE 7 DAY
FORECAST.

SERIES OF DATA ANALYSIS THROUGH 19Z SHOWS A COLD FRONT EXTENDING
FROM EASTERN SOUTH DAKOTA...NORTHEAST THROUGH NORTHERN WISCONSIN.
THE CONVECTIVE COMPLEX WHICH DEVELOPED NORTH OF THIS BOUNDARY FRIDAY
IS NOW MOVING THROUGH CENTRAL MINNESOTA.  EASTWARD PROPAGATION OF
THIS COMPLEX HAS SLOWED TO LESS THAN 10 MPH.  OUTFLOW FROM IT HAS
MADE IT SOUTH OF A KMML-KULM-KRGK LINE.  DURING THE PAST
HOUR...CONVECTION HAS DEVELOPED NORTH OF THE COLD FRONT IN EASTERN
SOUTH DAKOTA AND SOUTHWESTERN MINNESOTA.  WOODLAKE PROFILER DATA
SHOWING 40 KNOTS AT 850 MB RIGHT INTO THE COMPLEX...WHICH CONTINUES
TO SUPPORT CONVECTION.

CONVECTION WILL CONTINUE TO DEVELOP ALONG THE FRONT THIS EVENING AS
CONVERGENCE INCREASES AND CAP /CURRENT CINS ABOUT 150 J/KG/
WEAKENS.  ETA BUFR SOUNDINGS IN BUFKIT AND 03/18Z RUC BOTH SHOW 0-3
KM SHEAR IN EXCESS OF 35 KNOTS...WITH WEAK MID LEVEL SHEAR /LESS
THAN 15 KNOTS/ ALONG THE FRONT.  THIS SUGGESTS MAINLY A WIND
EVENT...BUT LOCALIZED SHEAR ALONG THE FRONT COULD PRODUCE SOME
SPINUPS.

TONIGHT...EXPECT STRONG LOW LEVEL MOISTURE TRANSPORT TO INTERSECT
THE COLD FRONT AS IT EDGES SOUTH.  THIS WILL ORGANIZE STORMS INTO A
CONVECTIVE COMPLEX NORTH OF THE FRONT.  INITIAL MUCAPES IN EXCESS
OF 3500 J/KG SUGGESTS HAIL POTENTIAL...BUT DEEP WARM LAYER WILL WORK
AGAINST THIS.  CORFIDI VECTORS ON THE ETA SHOWS THAT THE SYSTEM WILL
POTENTIALLY BACKBUILD OVERNIGHT.  THIS IN CONJUNCTION WITH A DEEP
WARM LAYER /WET BULB ZERO HEIGHTS 14.5 KFT/ AND PRECIPITABLE WATERS
WELL ABOVE NORMAL SUGGESTS TORRENTIAL RAINFALL AMOUNTS POSSIBLE.
WILL OUTLINE IN ANOTHER ESF AND THE DATABASE AND WILL ALLOW THE
FOLLOWING SHIFTS TO ISSUE A FLOOD WATCH AS THE AREA AFFECTED BECOMES
MORE CLEAR.

THE FRONT WILL PUSH THROUGH THE FORECAST AREA SUNDAY.  THE SECOND
COMPLEX OF STORMS FORECAST BY THE AVN TO MOVE THROUGH THE FORECAST
AREA SUNDAY MAY BE A RESULTANT MODEL ERROR.  HOWEVER...LOW LEVEL
FORCING DOES EXIST IN THE MODEL FORECAST.  IN THE END...BELIEVE THE
SCENARIO FOR SUNDAY WILL BE FOCUSED ALONG THE FRONT...AS SUGGESTED
BY THE ETA.  OVERALL...LOW CONFIDENCE IN THIS SO WILL CONTINUE GOING
FORECAST OF A CHANCE OF CONVECTION...MOST CONCENTRATED ALONG THE
FRONT.

THE FRONT WILL CONTINUE SOUTHWEST AS AN UPPER LEVEL OMEGA BLOCK
DEVELOPS OVER THE PLAINS STATES.  THIS WILL BRING COOL EASTERLY
FLOW INTO THE FORECAST AREA DURING THE EARLY PORTION OF THE WEEK.
HOWEVER...MEDIUM RANGE ENSEMBLE MEAN AT 500 MB SHOWS A STRONG
POSITIVE ANAMOLY DEVELOPING RIGHT OVER THE REGION BY MIDWEEK.  THIS
WILL PUSH TEMPERATURES BACK ABOVE NORMAL...WITH READINGS QUITE WARM
BY THE END OF THE WEEK.  THE BLOCK SHOULD BREAK DOWN INTO NEXT
WEEKEND.  THIS WILL ALLOW ANOTHER COLD FRONT TO PUSH THROUGH THE
FORECAST AREA NEXT WEEKEND...COOLING US OFF WITH A CHANCE OF
THUNDERSTORMS.

COORDINATED WITH MPX/GBR.

.LSE...NONE.

KRC