Damaging Wind in Iowa, May 19, 2004

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
325 AM CDT WED MAY 19 2004

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT

SEVERE WEATHER THREAT TONIGHT IS THE MAIN FORECAST CONCERN WITH THIS
PACKAGE.

AT 3 AM...A 1023 MB SURFACE HIGH WAS CENTERED OVER NORTHERN LOWER
MICHIGAN. MEANWHILE...A COLD FRONT EXTENDED FROM INDIANAPOLIS TO ST LOUIS
TO WICHITA KANSAS. STRONG MOISTURE TRANSPORT ON THE NOSE OF A
850 MB JET HAS CAUSED A MESOSCALE CONVECTIVE COMPLEX TO DEVELOP
ACROSS THE DAKOTAS.

THERE WERE SOME INITIALIZATION PROBLEMS WITH THE MAY 19TH 00Z MODELS.
THE ETA WAS 3 TO 4C TOO WARM AT 850 MB AT NORTH PLATTE NEBRASKA AND
RAPID CITY SOUTH DAKOTA. WITH THE TRAJECTORY OF THIS AIRMASS TO OUR
NORTH AND WEST...THIS WILL NOT BE A FACTOR IN OUR FORECAST TODAY.
ANOTHER INITIALIZATION PROBLEM SHOWED UP IN BOTH THE GFS AND ETA DEW
POINTS AT GREEN BAY AND CHANHASSEN. BOTH MODELS WERE 2 TO 5C TOO
DRY AT 850 MB IN THESE LOCATIONS. THIS MAY BE IMPORTANT ON THE
INITIAL ONSET OF THE PRECIPITATION THIS AFTERNOON. FINALLY...THE
700 MB DEW POINT AT DODGE CITY KANSAS WAS INITIALIZED WAY TOO LOW.
THE ETA HAS IT INITIALIZED AT -44C AND THE ACTUAL 00Z SOUNDING SHOWS
THAT IT SHOULD BE -19C. THIS COULD HAVE BECOME A BIG DEAL BECAUSE
THE 700 MB TRAJECTORY WOULD HAVE THIS AIR MASS MOVING ACROSS OUR
AREA LATE THIS AFTERNOON AND EVENING. HOWEVER...THIS TOO LOW DEW
POINT QUICKLY VANISHED BY THE MAY 19TH 06Z PANEL AND THUS IT WILL
NOT AFFECT OUR FORECAST.

AS WAS THE CASE WITH PREVIOUS MODELS RUNS...THE BEST SEVERE WEATHER
THREAT WILL BE ACROSS WESTERN IOWA...EASTERN NEBRASKA...EXTREME
SOUTHEAST SOUTH DAKOTA...AND SOUTHWEST MINNESOTA THIS AFTERNOON AND
TONIGHT WHERE DEEP SHEAR AND VERY UNSTABLE CONDITIONS WILL EXIST.
THE CAP BREAKS MID TO LATE THIS AFTERNOON...THUNDERSTORMS WILL
QUICKLY BECOME SUPERCELLULAR ACROSS THIS AREA. THESE THUNDERSTORMS
WILL BE CAPABLE OF PRODUCING LONG LIVED TORNADOES. THESE
THUNDERSTORMS WILL EVENTUALLY EVOLVE INTO A MESOSCALE CONVECTIVE
COMPLEX THIS EVENING AND THIS SYSTEM WILL MOVE EAST ACROSS OUR AREA
TONIGHT. MOST UNSTABLE CAPES ON THE MAY 19TH 06Z ETA SHOWS VALUES OF
OVER 3000 J/KG ACROSS SOUTHEAST MINNESOTA AND NORTHEAST IOWA THIS
EVENING BETWEEN 03Z AND 06Z...AND THIS SPREADS ACROSS SOUTHWEST AND
WEST CENTRAL WISCONSIN BETWEEN 06Z AND 09Z. AS THE COLD POOL
DEVELOPS WITH THE THUNDERSTORM COMPLEX...DAMAGING WINDS WILL LIKELY
DEVELOP TO OUR WEST THIS EVENING AND THEN MOVE THROUGH THE AREA
OVERNIGHT TONIGHT. HOWEVER...WITH SOME DRY AIR MOVING IN ALOFT
DURING THE OVERNIGHT...I CANNOT RULE OUT SOME LARGE HAIL COMPLETELY.

THE COLD FRONT WILL MOVE SOUTH OF THE AREA ON THURSDAY AND THEN MOVE
SLOWLY NORTH ON THURSDAY NIGHT AND FRIDAY. THIS FRONT WILL LIKELY
LINGER ACROSS THE AREA ON FRIDAY NIGHT. THIS FRONT WILL BE THE FOCUS
OF SCATTERED SHOWERS AND THUNDERSTORMS DURING THIS TIME FRAME.

.LONG TERM...SATURDAY THROUGH TUESDAY

THE MEDIUM MODELS ARE IN VERY GOOD AGREEMENT THAT THE FRONTAL
BOUNDARY WILL REMAIN ACROSS THE AREA ON SATURDAY AND SATURDAY NIGHT.
HOWEVER...ON SUNDAY AND SUNDAY NIGHT THERE ARE SOME DIFFERING
OPINIONS OF THE EXACT LOCATION OF THIS FRONT. THE GFS PUSHES THIS
FRONT SOUTH INTO CENTRAL IOWA AND CENTRAL ILLINOIS. MEANWHILE...THE
ECMWF HAS THE FRONT SITUATED FURTHER NORTH ACROSS NORTHERN IOWA AND
NORTHERN ILLINOIS. IN ADDITION...THE ECMWF CONTINUE TO SHOW A LOW
PRESSURE AREA MOVING ALONG THIS FRONT DURING THIS TIME FRAME.
DUE TO THIS...THE PRECIPITATION CHANCES STILL LOOK GOOD FOR THIS
WEEKEND.

THE MEDIUM RANGE MODELS ARE IN FAIRLY GOOD AGREEMENT THAT THE FRONT
WILL CONTINUE TO BE LOCATED IN OUR VICINITY THROUGH MUCH OF NEXT
WEEK. AS A RESULT...WE MAY HAVE TO RE-EVALUATE OUR DRY FORECAST FOR
MONDAY AND TUESDAY.

&&

.ARX...WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
MN...NONE.
WI...NONE.

&&

BO

****ERROR: INCOMPLETE DATA

HAZARDOUS WEATHER OUTLOOK...CORRECTION
NATIONAL WEATHER SERVICE LA CROSSE WI
535 AM CDT WED MAY 19 2004

IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-032>034-
041>044-053>055-061-201100-
ADAMS-ALLAMAKEE-BUFFALO-CHICKASAW-CLARK-CLAYTON-CRAWFORD-DODGE-
FAYETTE-FILLMORE-FLOYD-GRANT-HOUSTON-HOWARD-JACKSON-JUNEAU-LA CROSSE-
MITCHELL-MONROE-MOWER-OLMSTED-RICHLAND-TAYLOR-TREMPEALEAU-VERNON-
WABASHA-WINNESHIEK-WINONA-
535 AM CDT WED MAY 19 2004

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

.DAY ONE...TODAY AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE ENTIRE AREA
TODAY AND TONIGHT. A SURFACE LOW PRESSURE SYSTEM WILL STRENGTHEN
ACROSS WESTERN NORTH DAKOTA TODAY. THIS LOW WILL MOVE EAST
INTO NORTHWEST MINNESOTA BY EVENING AND ACROSS ONTARIO OVERNIGHT.
A SURFACE BOUNDARY NOW OVER THE CENTRAL PLAINS TO THE OHIO VALLEY
WILL RETURN NORTHWARD AS A WARM FRONT LATE THIS AFTERNOON. THIS
BOUNDARY...COMBINED WITH A COLD FRONT MOVING ACROSS THE NORTHERN
PLAINS WILL BE THE FOCAL POINT FOR THUNDERSTORM DEVELOPMENT.
WITH THE DEEPEST SHEAR AND STRONGEST INSTABILITIES TO OUR WEST THIS
AFTERNOON...THUNDERSTORMS ARE EXPECTED TO DEVELOP IN SOUTHEASTERN
SOUTH DAKOTA...SOUTHWEST MINNESOTA AND WESTERN IOWA. AS THESE
STORMS MOVE EASTWARD THEY WILL LIKELY EVOLVE INTO ONE OR MORE
COMPLEXES OF STORMS WHICH WILL MOVE ACROSS THE AREA LATER THIS
EVENING. THE MAIN THREAT LOOKS TO BE DAMAGING WINDS AND TO A
LESSER DEGREE SOME LARGE HAIL.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE COLD FRONT WILL MOVE SOUTH OF THE AREA ON THURSDAY...THEN RETURN
NORTH ONCE AGAIN LATER THURSDAY NIGHT INTO FRIDAY. THIS BOUNDARY
LOOKS TO REMAIN OVER THE AREA RIGHT THROUGH THE WEEKEND. THUS
PERIODS SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH WEEKEND. THE
THREAT OF SEVERE WEATHER WILL BE DETERMINED BY THE EXACT LOCATION
OF THE FRONT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE LIKELY THIS AFTERNOON AND NIGHT...
GENERALLY AFTER 4 PM.

RABERDING