Severe Thunderstorm Warning 19, NWS La Crosse, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
235 PM CDT TUE MAY 12 1998

FORECAST CONCERNS TONIGHT...TIMING/COVERAGE OF LATE AFTERNOON EARLY
EVENING SHRA/TSRA ACROSS THE AREA...SEVERE RISK...OVERNIGHT LOWS.

AT 18Z THE SURFACE LOW WAS NEAR KAXN...WITH A COLD FRONT NEAR A KAXN-
KULM-KDSM-KMCI LINE.  AIRMASS JUST EAST OF THE FRONT WAS QUITE UNSTABLE
WITH DEWPOINTS IN THE LOWER 60S...CAPES OF 1200-1800 J/KG...LI/S OF
-3 TO -5...AND NO CAP.  LATEST RAMSDIS WV LOOP SHOWS THE SHORTWAVE IN
WEST CENTRAL MN.  12Z ETA HAD BEST HANDLE THESE POSTIONS. LATEST
RAMSDIS VIS PICTURES SHOW SCATTERED-BROKEN CUMULUS DECK OVER THE WEST
HALF OF THE AREA...ABOUT TO PUSH EAST OF THE MS RIVER.

12Z MODELS REASONABLY SIMILAR BUT ETA FAVORED AS IT WAS MUCH CLOSER TO
REALITY AT 18Z.  SEVERAL FACTORS IN PLACE FOR SLIGHT RISK OF SEVERE
TSRA ACROSS THE AREA TIL ABOUT 02Z-03Z THIS EVENING.  THE STRONG
SHORTWAVE IN MN SWINGS A VORT LOBE ACROSS THE AREA...THE APPROACHING
FRONT WITH ITS LOW LEVEL CONVERGENCE/FROTOGENTICAL FORCING...AND THE
UNSTABLE AIRMASS AHEAD OF THE FRONT.

NEGATIVE FACTORS...LACK OF CAPPING TO FOCUS CONVECTION ON THE FRONT...
/WHEN IT GOES...IT ALL GOES/...AND THE CUMULUS DECK SPREADING ACROSS
THE AREA TO RETARD LATE AFTERNOON WARMING/LOW LEVEL INSTABILITY.

AT 1915Z...AT LEAST SCATTERED SHRA/TSRA EXPECTED TO FIRE ALONG THE COLD
FRONT...THEN PUSHING EAST ACROSS THE AREA THRU THE LATE AFTERNOON/EARLY
EVENING HOURS.  PRECIPITATION CHANCES DROP OFF QUICKLY AFTER FROPA AS
DRIER LOW/MID LEVEL AIR PUSHES IN BEHIND IT. THE LOW AND SHORTWAVE LIFT
RATHER QUICKLY NORTHEAST OF THE AREA OVERNIGHT...WITH HIGH PRESSURE...
SINKING AND DRYING AIR TO SPREAD ACROSS THE AREA IN ITS WAKE LATER
TONGIHT.

GUIDANCE POPS GENERALLY RAISED WITH EXPECTATIONS OF A LINE OF SHRA/TSRA
PUSHING ACROSS THE AREA FROM 21Z-02Z.  GUIDANCE TEMPS LOOK GOOD...USED
A BLEND OF THE NGM-FWC/AVN-FAN/ETA 2M GRIDPOINTS FOR LOWS.

RRS

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-131200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
1125AM CDT TUE MAY 12 1998

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON INTO
EARLY THIS EVENING ACROSS ALL OF NORTHEAST IOWA...SOUTHEAST MINNESOTA
AND MUCH OF WESTERN WISCONSIN...

IN WISCONSIN...THE SLIGHT RISK AREA IS GENERALLY WEST OF AN EAU CLAIRE
TO WISCONSIN DELLS LINE.

A COLD FRONT FROM SOUTHWEST MINNESOTA INTO CENTRAL IOWA LATE THIS
MORNING WILL CONTINUE PUSHING EAST THIS AFTERNOON.  AN UPPER LEVEL
DISTURBANCE WILL ALSO BE PASSING OVER MINNESOTA LATER TODAY TO AID THE
LIFTING OF THE AIRMASS ALONG THE FRONT.

A WARM...MOIST AIRMASS AHEAD OF THE FRONT WILL PROVIDE THE FUEL FOR
SHOWERS AND THUNDERSTORMS ACROSS THE AREA LATER THIS AFTERNOON AND
EARLY THIS EVENING.  A FEW OF THESE STORMS MAY BECOME SEVERE WITH LARGE
HAIL AND DAMAGING WINDS...MAINLY BETWEEN THE HOURS OF 3 PM AND 8 PM.

ACTIVATION OF SPOTTER GROUPS MAY BE NEEDED LATER THIS AFTERNOON AND
THIS EVENING.  MONITOR YOUR FAVORITE SOURCE OF WEATHER INFORMATION FOR
LATER UPDATES REGARDING THE SLIGHT RISK OF SEVERE THUNDERSTORMS FOR THE
AREA LATER TODAY.

RRS

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-
032>034-041>044-053>055-061-130300-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LA CROSSE WI
420 PM CDT TUE MAY 12 1998

...A SEVERE THUNDERSTORM WATCH HAS BEEN ISSUED FOR MUCH OF THE AREA
UNTIL 10 PM THIS EVENING...

IN MINNESOTA THIS WATCH IS GENERALLY EAST OF A RED WING TO ROCHESTER TO
PRESTON LINE.  IN IOWA THIS WATCH IS EAST OF A CRESCO TO OELWEIN LINE.

IN WISCONSIN...THE WATCH IS IN EFFECT FOR ABOUT THE WESTERN HALF OF THE
STATE...WEST OF A MEDFORD...WISCONSIN RAPIDS...MADISON LINE.

A COLD FRONT IN CENTRAL MINNESOTA AND IOWA LATE THIS AFTERNOON WILL
CONTINUE TO PUSH EAST AND MOVE THROUGH THE WATCH AREA DURING THE REST
OF THE AFTERNOON AND EVENING HOURS.  A MOIST AND UNSTABLE AHEAD OF THE
FRONT WILL PROVIDE THE FUEL FOR SHOWERS AND THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING.  SOME OF THESE STORMS MAY BECOME SEVERE...WITH
LARGE HAIL AND DAMAGING WINDS.

IF YOU LIVE IN AND CLOSE TO THE WATCH AREA...REMAIN ALERT TO CHANGING
WEATHER CONDITIONS.  MONITOR YOUR FAVORITE SOURCE OF WEATHER
INFORMATION FOR LATER UPDATES AND POSSIBLE SEVERE WEATHER WARNINGS.

RRS