Severe Thunderstorm Warning 97, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
300 AM CDT MON AUG 23 1999

PRIMARY FORECAST CONCERNS...RAIN CHANCES TODAY THROUGH TUESDAY.

07Z SURFACE MAP INDICATED LOW PRESSURE JUST NORTH OF MN/CANADIAN BORDER
WITH COLD FRONT EXTENDING ACROSS NORTHWEST MN INTO SOUTHEAST SOUTH
DAKOTA AND EASTERN NEBRASKA. THUNDERSTORMS ACCOMPANYING THE COLD FRONT
THROUGH NORTHERN AND WESTERN MN...HEADING SOUTHEAST. IN THE UPPER
LEVELS...VIGOROUS SHORT WAVE NOTED IN WATER VAPOR SATELLITE IMAGERY
OVER EASTERN NORTH DAKOTA...ALSO HEADING SOUTHEAST.

00Z MODELS WERE SIMILAR IN TAKING THE UPPER LEVEL CIRCULATION INTO IOWA
BY 00Z THIS EVENING...THEN EXITING IT INTO IL OVERNIGHT AND OHIO VALLEY
ON TUESDAY. STRONG PV-ADVECTION IN THE 200-400 MB LAYER ALONG WITH
CONVERGENCE AHEAD OF THE APPROACHING SURFACE FRONT WILL PROVIDE LARGE
SCALE ASCENT TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE
FORECAST AREA TODAY.

SHORT WAVE AND ASSOCIATED LIFT EXITING THIS EVENING...SO ANY LINGERING
SHOWERS EXPECTED TO END. TIME/HEIGHT CROSS SECTIONS SHOWED 70 PERCENT
OR GREATER RELATIVE HUMIDITY BELOW 700 MB TONIGHT AND INTO TUESDAY.
WITH LIGHT WINDS AND ABUNDANT LOW LEVEL MOISTURE...LOW CLOUDS AND FOG
EXPECTED TO FORM OVERNIGHT. ON TUESDAY...MORNING CLOUDS AND FOG SHOULD
LIFT...THEN LOW LEVEL MOISTURE CONVERGENCE INDICATED BY BOTH ETA AND
NGM...PRIMARILY ACROSS THE WI ZONES. THIS COMBINED WITH LINGERING
CYCLONIC FLOW FROM SURFACE LOW TO OUR SOUTH SHOULD RESULT IN A CHANCE
OF SHOWERS AS INDICATED IN CURRENT FORECAST.

TEMPERATURES A BIT PROBLEMATIC AGAIN TODAY. CLOUDS AND SHOWERS SHOULD
PREVENT READINGS FROM RISING TOO MUCH...SO EXPECT THIS AFTERNOON HIGHS
IN THE MIDDLE TO UPPER 70S...WHICH AGREED WITH FWC...FAN AND ETA 2M
VALUES. SIMILAR NUMBERS ANTICIPATED ON TUESDAY.

.LSE...NONE.

THOMPSON

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-231800-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
530 AM CDT MON AUG 23 1999

SCATTERED THUNDERSTORMS ARE ANTICIPATED THIS AFTERNOON ACROSS THE
AREA. NO RISK OF ORGANIZED SEVERE WEATHER HAS BEEN POSTED BY THE STORM
PREDICTION CENTER FOR OUR AREA.  HOWEVER...ISOLATED STRONG TO SEVERE
THUNDERSTORMS COULD DEVELOP...MAINLY ACROSS SOUTHWEST WISCONSIN AND
NORTHEAST IOWA LATER THIS AFTERNOON.  THE MAIN THREAT IS LARGE HAIL.

A VIGOROUS UPPER LEVEL LOW PRESSURE CENTER WILL MOVE ACROSS THE AREA
FROM NORTHWEST TO SOUTHEAST TODAY.  THIS WILL CAUSE THE ATMOSPHERE TO
BECOME UNSTABLE...ESPECIALLY DURING THE WARMEST PORTION OF THE
AFTERNOON...IN AREAS WHERE SOME SUNSHINE REACHES THE SURFACE. ALTHOUGH
THE WIND PROFILE IS NOT CONDUCTIVE FOR LONG-LIVED STORMS...ISOLATED
LARGE HAIL COULD RESULT FROM THE STRONGER STORMS. DUE TO THE ISOLATED
NATURE OF THE POSSIBLE THUNDERSTORMS THIS AFTERNOON...SPOTTER ACTIVATION
IS NOT EXPECTED.

DB

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-231800-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
530 AM CDT MON AUG 23 1999

SCATTERED THUNDERSTORMS ARE ANTICIPATED THIS AFTERNOON ACROSS THE
AREA. NO RISK OF ORGANIZED SEVERE WEATHER HAS BEEN POSTED BY THE STORM
PREDICTION CENTER FOR OUR AREA.  HOWEVER...ISOLATED STRONG TO SEVERE
THUNDERSTORMS COULD DEVELOP...MAINLY ACROSS SOUTHWEST WISCONSIN AND
NORTHEAST IOWA LATER THIS AFTERNOON.  THE MAIN THREAT IS LARGE HAIL.

A VIGOROUS UPPER LEVEL LOW PRESSURE CENTER WILL MOVE ACROSS THE AREA
FROM NORTHWEST TO SOUTHEAST TODAY.  THIS WILL CAUSE THE ATMOSPHERE TO
BECOME UNSTABLE...ESPECIALLY DURING THE WARMEST PORTION OF THE
AFTERNOON...IN AREAS WHERE SOME SUNSHINE REACHES THE SURFACE. ALTHOUGH
THE WIND PROFILE IS NOT CONDUCTIVE FOR LONG-LIVED STORMS...ISOLATED
LARGE HAIL COULD RESULT FROM THE STRONGER STORMS. DUE TO THE ISOLATED
NATURE OF THE POSSIBLE THUNDERSTORMS THIS AFTERNOON...SPOTTER ACTIVATION
IS NOT EXPECTED.

DB