Severe Thunderstorm Warning 146, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
320 PM CDT SUN SEP 10 2000

PRIMARY CONCERNS...THUNDERSTORM CHANCES TONIGHT AND MONDAY AS
WELL AS SEVERE WEATHER POTENTIAL.

AS OF 20Z...SURFACE ANALYSIS INDICATED FRONTAL BOUNDARY EXTENDED
ACROSS THE FORECAST AREA FROM ABOUT AUSTIN MN THROUGH LA CROSSE AREA
AND INTO NORTHEAST WI. SOUTH OF THE FRONT...AIR MASS VERY MOIST AND
UNSTABLE WITH TEMPERATURES IN THE 80S AND DEWPOINTS AROUND 70. WATER
VAPOR LOOPS SHOWED SHORT WAVES MOVING ACROSS SOUTHERN CANADA AND
PACIFIC NORTHWEST IN FAST ZONAL FLOW.

VERY GOOD INITIALIZATION OF 12Z MODELS WITH RESPECT TO UPPER AIR
AND SURFACE FEATURES. MODELS IN GENERAL AGREEMENT ON SHORT WAVE
ENERGY AMPLIFYING TROUGH OVER THE NORTH CENTRAL STATES ON MONDAY...
WHICH WILL DRIVE A STRONG COLD FRONT ACROSS THE UPPER MISSISSIPPI
VALLEY...SETTING THE STAGE FOR POTENTIAL SEVERE WEATHER EVENT.

WARM AIR ADVECTION AND STRONG THETA-E ADVECTION RETURN TONIGHT...
WHICH IS EXPECTED TO INITIATE CONVECTION OVER THE FORECAST AREA.
FORECAST SOUNDINGS INDICATED 2000-3000 J/KG CAPE ABOVE THE BOUNDARY
LAYER...SO PLENTY OF ELEVATED INSTABILITY AVAILABLE FOR A FEW STRONG
STORMS...BUT ORGANIZED SEVERE STORMS NOT ANTICIPATED.

ON MONDAY...APPROACH OF AMPLIFYING UPPER LEVEL TROUGH AND ASSOCIATED
UPPER LEVEL DIVERGENCE...COUPLED WITH STRONG LOW LEVEL CONVERGENCE IN
VICINITY OF APPROACHING COLD FRONT ALL POINT TO SEVERE WEATHER
POTENTIAL. CAPE REACHES 3500-4500 J/KG AND CONVECTIVE INHIBITION OF
50 J/KG OR BELOW. BULK RICHARDSON NUMBERS OF 45 OR GREATER SUPPORT
POTENTIAL SQUALL LINE DEVELOPMENT AHEAD OF THE COLD FRONT. FRONT
EXPECTED TO SWEEP OUT OF THE AREA MONDAY EVENING...TAKING THE STORMS
WITH IT.

TEMPERATURES FOR MONDAY STILL PROBLEMATIC DUE TO UNCERTAINTY OF
CLOUD DEBRIS THAT WILL BE LEFTOVER FROM OVERNIGHT CONVECTION.
FORECAST SOUNDINGS SUGGEST HIGHS WILL REACH THE LOWER TO MIDDLE
80S...EXCEPT UPPER 70S IN NORTH CENTRAL WI WHERE CLOUD COVER MAY
LINGER. AIR MASS ON MONDAY WILL BE QUITE HUMID AS WELL WITH DEWPOINTS
EXPECTED TO BE AROUND 70. MUCH LESS HUMIDITY AND COOLER AIR EXPECTED
TUESDAY WITH HIGHS IN THE UPPER 60S TO MIDDLE 70S.

THANKS TO MKX...MPX AND DMX FOR COORDINATION TODAY.

.LSE...NONE.

THOMPSON

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-032>034-
041>044-053>055-061-110200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
546 PM CDT SUN SEP 10 2000

...SLIGHT RISK OF SEVERE WEATHER TONIGHT ACROSS THE REGION...

A FRONT HAS BECOME STATIONARY ACROSS THE AREA STRETCHING FROM
NORTHEAST WISCONSIN DOWN INTO SOUTHEAST MINNESOTA...THEN INTO
NORTHERN IOWA. THE ATMOSPHERE TO THE SOUTH OF THIS BOUNDARY HAS
BECOME VERY UNSTABLE THIS AFTERNOON.  THE BOUNDARY IS EXPECTED TO
BEGIN LIFTING TO THE NORTH THIS EVENING...AS THE LOW LEVEL JET
INCREASES IN SPEED. THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG
AHEAD OF THIS FRONT.

THE INSTABILITY AND WIND PROFILES ACROSS THE REGION SHOULD BE
SUFFICIENT TO GENERATE SOME SEVERE THUNDERSTORMS. THE MAIN THREAT OF
SEVERE WEATHER WILL BE LARGE HAIL...BUT ISOLATED DAMAGING WINDS WILL
BE POSSIBLE.

SPOTTER ACTIVATION MAY BE REQUIRED LATER THIS EViENING.

NELSON

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-032>034-
041>044-053>055-061-110200-

HAZARDOUS WEATHER OUTLOOK...CORRECTED FOR WORDING
NATIONAL WEATHER SERVICE LA CROSSE WI
552 PM CDT SUN SEP 10 2000

...SLIGHT RISK OF SEVERE WEATHER TONIGHT ACROSS THE REGION...

A FRONT HAS BECOME STATIONARY ACROSS THE AREA STRETCHING FROM
NORTHEAST WISCONSIN DOWN INTO SOUTHEAST MINNESOTA...THEN INTO
NORTHERN IOWA. THE ATMOSPHERE TO THE SOUTH OF THIS BOUNDARY HAS
BECOME VERY UNSTABLE THIS AFTERNOON.  THE BOUNDARY IS EXPECTED TO
BEGIN LIFTING TO THE NORTH THIS EVENING...AS THE LOW LEVEL JET
INCREASES IN SPEED. THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG AND
AHEAD OF THIS FRONT.

THE INSTABILITY AND WIND PROFILES ACROSS THE REGION SHOULD BE
SUFFICIENT TO GENERATE SOME SEVERE THUNDERSTORMS. THE MAIN THREAT OF
SEVERE WEATHER WILL BE LARGE HAIL...BUT ISOLATED DAMAGING WINDS WILL
BE POSSIBLE.

SPOTTER ACTIVATION MAY BE REQUIRED LATER THIS EVENING.

NELSON