A line of thunderstorms along a cold front moved across northeast Iowa during the late afternoon hours on August 9th. The thunderstorms produced hail up to hen egg size near Decorah (Winneshiek County) and wind gust of 70 miles per hour near Calmar (Winneshiek County).
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS ARX wrote it up.
A line of thunderstorms along a cold front moved across northeast Iowa during the late afternoon hours on August 9th. The thunderstorms produced hail up to hen egg size near Decorah (Winneshiek County) and wind gust of 70 miles per hour near Calmar (Winneshiek County).
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS La Crosse, WI wrote its last area forecast discussion before the first event at Aug 9, 2:23 PM CST, 1 hour 27 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE LA CROSSE WI 323 PM CDT THU AUG 9 2012 .SHORT TERM...TONIGHT THROUGH SATURDAY 323 PM CDT THU AUG 9 2012 |MAIN FORECAST CONCERNS ARE ON ON LINGERING SHOWERS AND THUNDERSTORMS THIS EVENING AND PATCHY FOG AFTER MIDNIGHT. FOCUS THEN TURNS TO VALLEY FOG FRIDAY NIGHT INTO SATURDAY MORNING. LATEST WATER VAPOR IMAGERY SHOWED AN UPPER LOW OVER FAR NORTHWEST WISCONSIN DRIFTING SOUTHEAST. LATEST RADAR SHOWED SHOWERS AND THUNDERSTORMS DEVELOPING ACROSS MUCH OF SOUTHEAST MINNESOTA INTO WEST CENTRAL AND CENTRAL WISCONSIN. A FEW STORMS WERE PRODUCING SMALL HAIL. SOME OF THE STORMS COULD PRODUCE LARGE HAIL LATE THIS AFTERNOON INTO EARLY THIS EVENING. IN ADDITION...A FEW STORMS MAY PRODUCE GUSTY WINDS. THE UPPER LOW WILL MOVE OVER SOUTHERN LAKE MICHIGAN TONIGHT WITH SHOWERS AND THUNDERSTORMS TAPERING OFF AND ENDING FROM WEST TO EAST ACROSS THE FORECAST AREA. FORECAST SOUNDINGS SHOW SATURATION NEAR THE SURFACE WITH WEAK LIFT AROUND THROUGH MUCH OF OF THE NIGHT. DESPITE WINDS FROM JUST ABOVE THE SURFACE THROUGH 1KFT AT 8 TO 20KTS...THERE APPEARS THAT ENOUGH DECOUPLING WILL OCCUR TO ALLOW FOR SOME PATCH SHALLOW FOG. AREAS THAT TYPICALLY DECOUPLE UNDER WEAK FLOW WILL HAVE THE HIGHEST CHANCES OF SEEING THE FOG OVERNIGHT. IN ADDITION...THE INTERNATIONAL FALLS SOUNDING THIS MORNING HAD A SIMILAR WIND PROFILE AND PATCHY FOG WAS SEEN ACROSS MUCH OF CENTRAL INTO NORTHERN MINNESOTA. CLOUDS WILL DECREASE ACROSS THE AREA TONIGHT WITH MOSTLY CLEAR SKIES EXPECTED BY LATE IN THE NIGHT. THIS WILL ALSO FAVOR SOME FOG DEVELOPMENT. PLAN ON LOWS TEMPERATURES RANGING FROM THE LOWER 50S ACROSS NORTHERN WISCONSIN TO THE MID 50S OVER NORTHEAST IOWA. FAVORED COLD AREAS SUCH AS SPARTA AND DIAMOND LAKE...WILL FALL INTO THE MID TO UPPER 40S. HIGH PRESSURE WILL BUILD INTO THE FORECAST AREA ON FRIDAY PROVIDING MOSTLY SUNNY SKIES. THE CLEAR SKIES AND A DRY AIR MASS MOVING IN WILL ALLOW FOR DEEP MIXING FRIDAY AFTERNOON. DECIDED TO LOWER DEW POINTS INTO THE 40S FRIDAY AFTERNOON DURING PEAK HEATING. PLAN ON HIGHS ON FRIDAY RANGING FROM THE LOWER 70S ACROSS NORTH CENTRAL WISCONSIN TO THE MID 70S OVER NORTHEAST IOWA. A RATHER CHILLY NIGHT IS IN STORE FOR THE REGION FRIDAY NIGHT WITH THE HIGH CENTERED OVER THE AREA. LOOK FOR LOWS TO FALL INTO THE LOWER 50S TO MID 40S. LOW LYING AREAS WILL DIP INTO THE LOWER 40S. CALM TO LIGHT WINDS WILL SET THE STAGE FOR WIDESPREAD VALLEY FOG ALONG THE WISCONSIN AND MISSISSIPPI RIVER VALLEYS. PLAN ON FOG REDUCING VISIBILITIES TO AROUND 1/4 MILE ACROSS THESE AREAS LATE FRIDAY NIGHT INTO EARLY SATURDAY MORNING. AFTER THE MORNING FOG...PLAN ON MOSTLY SUNNY SKIES ON SATURDAY WITH HIGH PRESSURE IN CONTROL. HIGH TEMPERATURES WILL RANGE FROM THE MID 70S ACROSS NORTH CENTRAL WISCONSIN TO THE UPPER 70S OVER NORTHEAST IOWA. A SHORTWAVE TROUGH WILL APPROACH THE UPPER MISSISSIPPI RIVER VALLEY SATURDAY NIGHT BRINGING A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS TO LOCATIONS WEST OF THE MISSISSIPPI RIVER...MAINLY AFTER MIDNIGHT. THE SHORTWAVE WILL PUSH EAST DURING THE DAY ON SUNDAY BRINGING SLIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS TO MUCH OF THE FORECAST AREA. FORECAST SOUNDINGS ARE VERY DRY ACROSS CENTRAL INTO PORTIONS OF SOUTHWEST WISCONSIN...WITH THE MAIN ENERGY FROM THE WAVE MOVING ACROSS IOWA. IF FORECAST MODEL TRENDS CONTINUE...PRECIPITATION CHANCES MAY NEED TO BE LOWERED EAST OF THE MISSISSIPPI RIVER DURING THE DAY ON SUNDAY. .LONG TERM...SUNDAY THROUGH THURSDAY 323 PM CDT THU AUG 9 2012 09.12 MEDIUM RANGE FORECAST MODELS SHOW THE TROUGH MOVING EAST EARLY ON MONDAY...WITH THE WAVE EXPECTED TO BE OVER LAKE MICHIGAN EXTENDING INTO THE OHIO RIVER VALLEY BY MONDAY AFTERNOON. SHOWER AND THUNDERSTORMS CHANCES WILL MOVE OUT OF THE AREA BY MONDAY AFTERNOON AS HIGH PRESSURE ATTEMPTS TO BUILD BACK IN. WARMER AIR WILL PUSH INTO THE REGION ON TUESDAY WITH HIGH BACK INTO THE UPPER 70S TO MIDDLE 80S. A WEAK SHORTWAVE IN NORTHWEST FLOW ALOFT WILL BRING LOW CHANCES FOR SHOWERS AND STORMS DURING THE DAY ON TUESDAY. A STRONGER TROUGH LOOKS TO PASS TO THE NORTH OF THE AREA WEDNESDAY INTO THURSDAY...DRAGGING A COLD FRONT ACROSS THE FORECAST AREA. WARMER AIR WILL MOVE INTO THE REGION AHEAD OF THE APPROACHING FRONT WITH WARM SOUTHERLY FLOW EXPECTED. PLAN ON HIGHS CLIMBING INTO THE LOWER TO UPPER 80S ON WEDNESDAY. AT THIS TIME...THE COLD FRONT IS EXPECTED TO MOVE ACROSS THE REGION THURSDAY BRINGING ANOTHER ROUND OF SHOWERS AND STORMS TO THE AREA. && .AVIATION...THROUGH 18Z FRIDAY 109 PM CDT THU AUG 9 2012 FORECAST CONCERNS THIS PERIOD ARE PRECIPITATION CHANCES THIS AFTERNOON...THEN STRATUS/FOG POTENTIAL OVERNIGHT. CLOSED UPPER LEVEL LOW CURRENTLY NEAR DULUTH SLIDING SOUTH...AND SCATTERED SHOWERS/STORMS DEVELOPING OUT AHEAD OF SURFACE COLD FRONT MOVING THROUGH. EXPECT HIGHEST CHANCE OF SHOWERS/STORMS AT KRST/KLSE THROUGH EARLY EVENING...THEN AS DRIER AIR WORKS IN AND LOSS OF DAYTIME HEATING...PRECIP WILL GRADUALLY SUBSIDE. MVFR CLOUDS WILL HANG ON AT KLSE THIS AFTERNOON...BEING CLOSER TO UPPER LOW AND STEADY EAST WINDS. AT KRST...EXPECTING A RISE TO VFR CEILINGS THIS AFTERNOON. ATTENTION TURNS TO WHETHER AMPLE LOW-LEVEL MOISTURE IN THE BOUNDARY LAYER WILL LEAD TO FOG AND/OR STRATUS OVERNIGHT. FORECAST SOUNDINGS SUGGEST BOUNDARY LAYER WINDS TO REMAIN HIGH ENOUGH FOR MIXING...EXCEPT FOR RIGHT NEAR SURFACE WHERE INVERSION DEVELOPS...TRAPPING ANY REMAINING MOISTURE. GIVEN CLOUDS/RAIN TODAY AND EXPECTED CLEARING TONIGHT...CONTINUED MVFR CONDITIONS AT BOTH TAF SITES. THERE IS POTENTIAL CONDITIONS COULD LOWER TO IFR...BUT CONFIDENCE ISN/T HIGH ENOUGH TO INCLUDE AT THIS POINT. && .ARX WATCHES/WARNINGS/ADVISORIES... 323 PM CDT THU AUG 9 2012 WI...NONE. MN...NONE. IA...NONE. && SHORT TERM...WETENKAMP LONG TERM...WETENKAMP AVIATION...ZT
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE LA CROSSE WI 221 PM CDT THU AUG 9 2012 IAZ008>011-018-019-029-030-MNZ079-086>088-094>096-WIZ017-029-032>034- 041>044-053>055-061-101100- 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- 221 PM CDT THU AUG 9 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST IOWA... SOUTHEAST MINNESOTA...SOUTHWEST INTO CENTRAL WISCONSIN. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING ACROSS MUCH OF THE AREA...WITH THE GREATER CHANCES EAST OF THE MISSISSIPPI RIVER. WIDESPREAD SEVERE WEATHER IS NOT EXPECTED...BUT AN ISOLATED SEVERE STORM WITH LARGE HAIL AND DAMAGING COULD OCCUR. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY THUNDERSTORMS ARE AGAIN POSSIBLE ON SUNDAY AND SUNDAY NIGHT. THE RISK FOR ANY SEVERE WEATHER IS LOW FOR THIS TIMEFRAME. ANOTHER THREAT FOR THUNDERSTORMS COMES IN FOR TUESDAY AND ESPECIALLY WEDNESDAY. THIS SYSTEM IS A LITTLE STRONGER...AND SEVERE STORMS CANNOT BE RULED OUT...ESPECIALLY DURING THE LATTER PART OF WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION SHOULD NOT BE NEEDED DUE THE ISOLATED NATURE OF THE SEVERE WEATHER THREAT. .EMERGENCY MANAGEMENT COORDINATION... NO WEBINAR IS SCHEDULED. 04
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 258 PM CDT THU AUG 9 2012 MNZ086-094-092100- DODGE-MOWER- 258 PM CDT THU AUG 9 2012 ...STRONG THUNDERSTORM MOVING ACROSS WESTERN DODGE AND MOWER COUNTIES... AT 253 PM...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM NEAR CLAREMONT...MOVING SOUTH AT 25 MPH. WIND GUSTS OF 40 TO 50 MPH...SMALL HAIL UP TO 1/2 INCH AND TORRENTIAL DOWNPOURS MAY ACCOMPANY THIS STRONG THUNDERSTORM. LOCATIONS THAT MAY BE AFFECTED INCLUDE... HIGHWAY 30 AND COUNTY 3...GRAVES LANDING FIELD...BROOKSIDE CAMPGROUND...WALTHAM...COUNTY ROADS 1 AND 15...LANSING AND MAYVILLE. SMALL HAIL MAY FALL FOR SEVERAL MINUTES AND COVER THE GROUND. THIS COULD LEAD TO DIFFICULT DRIVING CONDITIONS AND THE FORMATION OF FOG. ZT
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LA CROSSE WI
300 PM CDT THU AUG 09 2012
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0258 PM HAIL 4 NNE PLAINVIEW 44.22N 92.14W
08/09/2012 E0.88 INCH WABASHA MN TRAINED SPOTTER
0223 PM HAIL 3 SE LAKE CITY 44.42N 92.24W
08/09/2012 E0.50 INCH WABASHA MN PUBLIC
PEA TO MARBLE SIZE HAIL COVERED LAKE PEPIN GOLF COURSE
&&
SHEASPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 304 PM CDT THU AUG 9 2012 MNZ079-087-088-095-092100- FILLMORE-OLMSTED-WABASHA-WINONA- 304 PM CDT THU AUG 9 2012 ...STRONG THUNDERSTORMS MOVING THROUGH FILLMORE...OLMSTED...WABASHA AND WINONA COUNTIES... AT 302 PM...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER LITTLE VALLEY...MOVING SOUTH AT 30 MPH. SMALL HAIL UP TO 1/2 INCH AND TORRENTIAL DOWNPOURS MAY ACCOMPANY THIS THUNDERSTORM. LOCATIONS THAT MAY BE AFFECTED INCLUDE... WHITEWATER STATE PARK...HIGHWAY 42 AND COUNTY 9...COUNTY ROADS 9 AND 10...EYOTA...ST. CHARLES...DOVER...I 90 EXIT 233 AND I 90 EXIT 229. HEAVY RAIN COULD LEAD TO MINOR FLOODING OR A SHORT PERIOD OF STANDING WATER. STAY CLEAR OF DRAINAGE AREAS AND AVOID AREAS OF HIGH WATER IF THEY DEVELOP. SMALL HAIL MAY FALL FOR SEVERAL MINUTES AND COVER THE GROUND. THIS COULD LEAD TO DIFFICULT DRIVING CONDITIONS AND THE FORMATION OF FOG. ZT
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE LA CROSSE WI
330 PM CDT THU AUG 09 2012
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0320 PM HAIL 5 N ST. CHARLES 44.04N 92.06W
08/09/2012 E0.50 INCH WINONA MN AMATEUR RADIO
&&
DTJSPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 337 PM CDT THU AUG 9 2012 IAZ008>010-018-019-029-MNZ079-086>088-094>096-WIZ017-029-032>034-041- 092300- BUFFALO-CHICKASAW-CLARK-DODGE-FAYETTE-FILLMORE-FLOYD-HOUSTON-HOWARD- JACKSON-LA CROSSE-MITCHELL-MOWER-OLMSTED-TAYLOR-TREMPEALEAU-WABASHA- WINNESHIEK-WINONA- 337 PM CDT THU AUG 9 2012 ...STRONG THUNDERSTORMS MOVING ACROSS THE AREA... SCATTERED STRONG THUNDERSTORMS WILL CONTINUE TO MOVE THROUGH THE AREA OVER THE NEXT FEW HOURS. HAIL UP TO 1/2 INCH AND GUSTY WINDS UP TO 40 MPH CAN BE EXPECTED WITH THE STRONGER STORMS. PLAN ON LIGHTNING AND BRIEF HEAVY RAINFALL AS WELL..WITH AMOUNTS BETWEEN 1/10 AND 1/4 OF AN INCH. HAIL MAY FALL FOR SEVERAL MINUTES AND COVER THE GROUND. THIS COULD LEAD TO DIFFICULT DRIVING CONDITIONS AND THE FORMATION OF FOG. ZT
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE LA CROSSE WI 436 PM CDT THU AUG 9 2012 IAZ010-092230- WINNESHIEK- 436 PM CDT THU AUG 9 2012 AT 433 PM...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER CHIMNEY ROCK CAMPGROUND...MOVING SOUTH AT 25 MPH. WIND GUSTS OF 40 TO 50 MPH AND SMALL HAIL MAY ACCOMPANY THIS STRONG THUNDERSTORM. LOCATIONS THAT MAY BE AFFECTED INCLUDE... COUNTY ROADS W 20 AND A 34...HIGHWAY 52 AND COUNTY W 34...RIDGEWAY... STATE ROAD 9 AND 245TH STREET...DECORAH...CONOVER AND SPILLVILLE. THESE WIND GUSTS COULD BLOW AROUND OUTDOOR FURNITURE AND OTHER LIGHT OBJECTS. SMALL BRANCHES MAY ALSO FALL. SEEK SAFE SHELTER INSIDE A BUILDING. JW
The La Crosse radar (KARX), 81 km away, was scanning. The volume nearest the first event began at 21:50 UTC.
3 hail, 2 thunderstorm wind. Local standard time, as filed.
Hail ranging in size from quarters to golf ball was reported four miles east of Ridgeway. |The large hail damaged a camper.
Hail the size of hen eggs was reported two miles west of Decorah.
An estimated wind gust of 70 miles per hour occurred near the intersection of Conover Road and 195th Street northwest of Calmar.
An estimated a wind gust of 70 miles per hour occurred just outside of Calmar.
Hail up to the size of quarters fell two miles northeast of Calmar. The hail stripped corn of its leaves and created drifts in road ditches.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2012Every state in 2012This day in weather historyWarnings in Iowa, August 2012
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 403946, 403949, 403924, 403930, 403963.