Severe Thunderstorm Warning 168, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
300 PM THU SEP 18 1997

FORECAST CONCERNS TONIGHT...STRENGTH AND TIMING OF CONVECTION ACROSS THE
AREA.

AT 18Z...SURFACE ANALYSIS HAD A LOW IN NORTHEAST SD...MOVING EAST-NORTH
EAST.  A WARM FRONT EXTENDED EAST FROM THE LOW THRU CENTRAL MN INTO
NORTHWEST WI...WHILE THE COLD FRONT WAS BEGINNING TO SURGE INTO SOUTH-
CENTRAL SD AND NW NEBRASKA.  DEWPOINTS HAD INCREASED INTO THE UPPER
60S AND LOW 70S IN THE WARM SECTOR AHEAD OF THE LOW...AS INDICATED BY
THE 17/12Z ETA.   AIRMASS IN THE WARM SECTOR WELL CAPPED EARLY THIS
AFTERNOON.

12Z ETA MODEL OF CHOICE THIS CYCLE...AS HAS BEEN PAST FEW RUNS.  AT
18Z...ETA APPEARS TO BE DOING A BETTER JOB WITH THE SURFACE PRESSURE
PATTERN AND 850/700MB VERICAL MOTION FIELDS.  CONVECTION WAS STARTING
TO FIRE IN NORTHERN MN.  THIS IN THE AREA OF BEST LOW LEVEL
CONVERGENCE...WARM ADVECTION...PRESSURE FALLS...THETA-E ADVECTION AND
DIFFERENTIAL DIVERGENCE.  THIS CONVECTION EXPECTED TO CONTINUE
DEVELOPING SOUTHWEST TOWARD THE 30-40 KNOT LOW LEVEL JET AND BEST
INSTABILITY THIS AFTERNOON...THEN PUSH SOUTHEAST TONIGHT.

12Z MODELS ARE SIMILAR IN KEEPING THE UPPER JET AXIS AND BEST SHORTWAVE
ENERGY NORTH OF THE FORECAST AREA THRU TONIGHT.  MODELS ALSO SIMILAR IN
SLOWING UP THE COLD FRONT AS IT PUSHES SOUTHEAST ACROSS THE FORECAST
AREA TONIGHT...BRINGING IT TO NEAR A KAUW-KLSE-KOMA LINE BY 19/12Z.
WITH WARM SECTOR WELL CAPPED AND LITTLE IN THE WAY OF UPPER DYNAMICS
TO AID LIFTING...INITIATION OF CONVECTION WILL HAVE TO WAIT FOR LOW
LEVEL CONVERGENCE ALONG THE FRONTS.

THE LATER TIMING OF THE FRONT INTO THE FORECAST AREA WILL ALSO LIMIT
THE SEVERE THREAT ACROSS THE AREA.  THE MAIN SEVERE THREAT APPEARS TO
BE WEST AND NORTH OF KLSE...WHERE STORMS MAY BE EARLY ENOUGH TO TAP THE
BETTER INSTABILITY UNDER THE CAP...BEFORE DIURNAL COOLING DECREASES IT.

NGM-FWC CLOSE ON LOWS WED NIGHT.  FWC/AVN-FAN TEMPERATURE GUIDANCE
SIMILAR FOR TONIGHT AND LOOKS GOOD...WITH MOSTLY CLOUDY SKIES AND
SOUTH-SOUTHWEST WINDS STAYING IN THE 10-15 MPH RANGE.  HIGHER FAN
POPS PREFERRED OVER FWC.

RRS

WIZ033-034-041>044-053>055-061-190040-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LA CROSSE WI
436 PM CDT THU SEP 18 1997

...THUNDERSTORMS WITH SMALL HAIL IN WEST CENTRAL AND CENTRAL
WISCONSIN...

AT 430 PM...DOPPLER RADAR SHOWED STRONG THUNDERSTORMS IN ADJACENT
AREAS EAST AND SOUTH OF LA CROSSE MOVING NORTHEAST AT 40 MPH. STORMS
WERE OCCURRING JUST NORTH OF THE ADAMS-FRIENDSHIP AREA OR ABOUT 20
MILES SOUTH OF WISCONSIN RAPIDS. PEA SIZE HAIL WAS REPORTED IN TOMAH
AROUND 4 PM.

THUNDERSTORMS WITH HAIL AND GUSTY WINDS UP TO 40 MPH CAN BE
EXPECTED EARLY THIS EVENING IN AREAS EAST AND SOUTH OF LA CROSSE.
THESE STORMS SHOULD ALSO CONTINUE MOVING THROUGH CENTRAL
WISCONSIN...INCLUDING MAUSTON AND FRIEDNSHIP AREAS.

IF A STORM SHOULD AFFECT YOUR AREA...GO INDOORS UNTIL IT PASSES.

THOMPSON

WIZ033-034-041>044-053>055-061-190040-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LA CROSSE WI
436 PM CDT THU SEP 18 1997

...THUNDERSTORMS WITH SMALL HAIL IN WEST CENTRAL AND CENTRAL
WISCONSIN...

AT 430 PM...DOPPLER RADAR SHOWED STRONG THUNDERSTORMS IN ADJACENT
AREAS EAST AND SOUTH OF LA CROSSE MOVING NORTHEAST AT 40 MPH. STORMS
WERE OCCURRING JUST NORTH OF THE ADAMS-FRIENDSHIP AREA OR ABOUT 20
MILES SOUTH OF WISCONSIN RAPIDS. PEA SIZE HAIL WAS REPORTED IN TOMAH
AROUND 4 PM.

THUNDERSTORMS WITH HAIL AND GUSTY WINDS UP TO 40 MPH CAN BE
EXPECTED EARLY THIS EVENING IN AREAS EAST AND SOUTH OF LA CROSSE.
THESE STORMS SHOULD ALSO CONTINUE MOVING THROUGH CENTRAL
WISCONSIN...INCLUDING MAUSTON AND FRIEDNSHIP AREAS.

IF A STORM SHOULD AFFECT YOUR AREA...GO INDOORS UNTIL IT PASSES.

THOMPSON