Hail and Damaging Winds in Iowa, July 20, 2003

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
255 PM CDT SUN JUL 20 2003

MAIN FORECAST FOCI...CONVECTION TONIGHT/AMOUNT OF COOLING AND COLD
POOL INSTABILITY THROUGH THE MIDDLE OF THE WEEK/WARMING AND
CONVECTIVE CHANCES WITH NEXT FRONT THE FOLLOWING WEEKEND.

500 MB NORTHWEST FLOW REGIME CONTINUES FOR NEARLY MUCH OF THE NEXT 5
DAYS.  THEN THE TREND FROM THE ECMWF/GFS IS TO FLATTEN THE FLOW TO
A MORE EAST-WEST SCENARIO OR EVEN SOUTHWESTERLY BY NEXT WEEKEND.

DATA ANALYSIS THROUGH 18Z SHOWING ONGOING PRECIPITATION SOUTHWEST OF
A KMKT-KDBQ LINE.  THIS IS THE REMNANTS OF LAST NIGHTS MCS.
BLOWOFF FROM THESE STORMS HAS LIMITED THE INSTABILITY OVER THE
FORECAST AREA.  ANOTHER AREA OF DEVELOPING STORMS IS ACROSS THE
INTERNATIONAL BORDER AND EXTEND TO NEAR KHYR.  THIS AREA HAS BECOME
UNSTABLE WITH THE ABSENCE OF DEBRIS CLOUDS.  THINK THE NORTHERN
PORTION OF THE FORECAST AREA NEAR THE PASSING DISTURBANCE IS NOW THE
MOST FAVORABLE FOR SEVERE WEATHER.  0-6KM SHEAR APPROACHING 60 KNOTS
SUGGESTS SHEAR PROFILES FAVORABLE FOR SUSTAINED UPDRAFTS/SUPERCELLS
PRODUCING LARGE HAIL.  VGPS DO NOT FAVOR TORNADIC SUPERCELLS AT THIS
TIME.

TO THE SOUTH...ON GOING CONVECTION SHOULD INCREASE THIS EVENING AS
NOCTURNAL JET REDEVELOPS.  HOWEVER...THIS SHOULD OCCUR MAINLY ACROSS
IOWA AND NORTHERN ILLINOIS.  EXPECT THE SEVERE WEATHER ASSOCIATED
WITH THIS COMPLEX TO REMAIN OUT OF THE FORECAST AREA.  ETA/RUC
SHOWING A BETTER HANDLE ON THE CONVECTIVE TRENDS AT 18Z THAN THE
GFS.  THE GFS IS TOO FAR NORTH WITH THE MCS MOVING ACROSS THE
SOUTHWESTERN PORTION OF THE FORECAST AREA. DID MOVE UP TIMING OF
PRECIPITATION EXITING THE FORECAST AREA BASED ON CONVECTIVE
TRENDS.

AS THE DISTURBANCE MOVES THROUGH TONIGHT IT WILL LOWER HEIGHTS AND
INCREASE THE COLD POOL IN THE MID LEVELS.  THIS INSTABILITY AND
RESIDUAL LOW LEVEL MOISTURE WILL CAUSE CLOUDS TO DEVELOP DURING THE
DAYTIME HOURS WITH ISOLATED AFTERNOON/EVENING SHOWERS.  THIS IS
SUPPORTED BY THE TQ INDEX AS WELL.

THE AIRMASS BEGINS TO MODIFY THURSDAY AS WINDS GRADUALLY BECOME
SOUTHERLY AHEAD OF THE NEXT SYSTEM.  BY FRIDAY...A STRONG SURFACE
PRESSURE GRADIENT DEVELOPS OVER IOWA/MINNESOTA.  THIS SHOULD
INCREASE THE WARM ADVECTION ACROSS THE FORECAST AREA.  ENSEMBLES
CONTINUE TO SHOW AN UPWARD TREND IN HIGH TEMPERATURES AND ARE NOW
NEAR OUR FORECAST HIGHS IN THE DATABASE.

HPC FORECAST SUGGESTS A SLOWER PROGRESSION OF THE COLD FRONT
APPROACHING THE FORECAST AREA NEXT FRIDAY.  THIS WOULD CAUSE THE
WARM ADVECTION AREA TO BE WEST OF THE FORECAST AREA...PRODUCING SOME
WARMING FRIDAY...BUT MOST SHOULD OCCUR SATURDAY.   THIS WOULD ALSO
DELAY THE BULK OF THE PRECIPITATION TO SATURDAY DAY/NIGHT TIME FRAME.

.LSE...WATCHES/WARNINGS/ADVISORIES...NONE.

KRC

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-032>034-
041>044-053>055-061-211100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
715 PM CDT SUN JUL 20 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
MINNESOTA...NORTHEAST IOWA...CENTRAL AND SOUTHWEST WISCONSIN.

.DAY ONE...TONIGHT

CONVECTION EARLIER IN THE DAY LEFT A REMNANT OUTFLOW BOUNDARY ACROSS
PARTS OF SOUTHERN MINNESOTA INTO NORTHEAST IOWA.  NEW THUNDERSTORMS
DEVELOPED NEAR THIS BOUNDARY LATE THIS AFTERNOON.  ADDITIONAL
SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE NEAR THIS BOUNDARY
DURING THE EVENING HOURS.  A FEW OF THE STORMS COULD BE STRONG WITH
SMALL HAIL OR DAMAGING WINDS.

MEANWHILE...AN UPPER LEVEL DISTURBANCE OVER SOUTHERN ONTARIO CANADA
IS MOVING SOUTHEAST TOWARD THE GREAT LAKES.  THIS DISTURBANCE IS
CLOSE ENOUGH TO PROVIDE SUPPORT FOR THUNDERSTORMS OVER NORTHERN
WISCONSIN AND CENTRAL MINNESOTA.  THE AIRMASS IN PLACE OVER THE
OUTLOOK AREA REMAINS MODERATELY UNSTABLE...AND WITH WIND SHEAR ALOFT
ALSO SUPPORTIVE FOR STRONG STORMS...THERE IS THE POTENTIAL FOR HAIL
AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY YET BE NEEDED TONIGHT...ESPECIALLY
OVER WISCONSIN.

MW