Thunderstorms developed in the early evening of September 4th in an unstable air mass over the region with lift from an upper-level disturbance that moved across the western Great Lakes region ahead of a stronger wave in the Northern Plains. CAPE values of 2000 J/kg to 2500 J/kg and 0-6 km bulk shear around 30 knots was sufficient to produce favorable conditions for sustained updrafts.
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 MKX wrote it up.
Thunderstorms developed in the early evening of September 4th in an unstable air mass over the region with lift from an upper-level disturbance that moved across the western Great Lakes region ahead of a stronger wave in the Northern Plains. CAPE values of 2000 J/kg to 2500 J/kg and 0-6 km bulk shear around 30 knots was sufficient to produce favorable conditions for sustained updrafts. These factors produced clusters of severe thunderstorms that developed along a weak convergent boundary that extended from northeast Minnesota through western Wisconsin. The clusters of supercell thunderstorms produced damaging wind gusts over a good portion of South-Central and Southeast Wisconsin.
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 Milwaukee, WI wrote its last area forecast discussion before the first event at Sep 4, 2:28 PM CST, 4 hours 12 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 328 PM CDT TUE SEP 4 2012 .TONIGHT AND WEDNESDAY...FORECAST CONFIDENCE...MEDIUM TO HIGH STILL WATCHING POTENTIAL FOR THUNDERSTORM DEVELOPMENT LATE THIS AFTERNOON AND INTO THE EVENING AS A WEAK SHORTWAVE AND SURFACE BOUNDARY APPROACH. STARTING TO SEE SOME RETURNS ON RADAR IN SOUTHEAST MN...SO STILL FEEL GOOD ABOUT LIKELY POPS IN THE WESTERN FORECAST AREA LATE AFTERNOON AND INTO THE EVENING. SEVERE STORMS POSSIBLE...WITH AROUND 30 KT 0-6KM BULK SHEAR TO GO ALONG WITH ROUGHLY 2000 J/KG CAPE. HAIL AND WIND ARE THE PRIMARY SEVERE CONCERNS. CONVECTION SHOULD WIND DOWN OR MOVE OUT BY LATE EVENING...WITH ATTENTION THEN TURNING WEST TOWARD THE APPROACHING MAIN SHORTWAVE AND SURFACE COLD FRONT. KEPT POPS CHANCE LATER TONIGHT...WITH LIKELY OR BETTER POPS WEDNESDAY AS THE TROUGH AND FRONT MOVE THROUGH. COULD SEE SOME STRONG TO SEVERE STORMS TOMORROW AS WELL...BUT MAY BE DIFFICULT WITH NOT MUCH TIME TO HEAT THINGS UP. BEST CHANCE FOR STRONGER STORMS WILL BE IN THE SOUTHEAST WHERE MORE HEATING MAY OCCUR. KEPT HIGHS UPPER 70S TO LOW 80S TOMORROW PER 925 MB TEMPS. MAY STRUGGLE TO GET THERE THOUGH IF CLOUDS AND PRECIP LINGER FOR MUCH OF THE DAY. .WEDNESDAY NIGHT AND THURSDAY...FORECAST CONFIDENCE IS HIGH. WILL CLEAR OUT ANY PRECIP BY 00Z THURSDAY. SOME OF THE MODELS HANG ONTO SOME PRECIP IN THE FAR SOUTHEAST CORNER PAST 00Z...BUT EXPECT THE DRIER AIR TO WORK IN PRETTY QUICK BEHIND THE FRONT. MOSTLY SUNNY WITH LOW DEWPOINTS ON THURSDAY. .THURSDAY NIGHT AND FRIDAY...FORECAST CONFIDENCE IS MEDIUM. A SIGNIFICANT UPPER LEVEL TROF WILL BE DROPPING DOWN OUT OF CANADA. THERE/S AN IMPRESSIVE FRONTOGENETIC RESPONSE WITH WARM ADVECTION DURING THIS PERIOD AS THE FLOW BACKS AHEAD OF IT. THE FAST FLOW WILL ALSO FEATURE A SERIES OF WEAK SHORT WAVES PASSING THROUGH. WE COULD SEE SOME RAIN SPREAD IN FROM THE WEST LATE THURSDAY NIGHT AND CONTINUE ON FRIDAY. RAINFALL LOOKS LIGHT IN GENERAL...WITH THE MAIN FOCUS DOWN OVER THE LOWER/MID MISSISSIPPI VALLEY...CLOSER TO THE ASSOCIATED LOW LEVEL CYCLOGENESIS. .SATURDAY THROUGH TUESDAY...FORECAST CONFIDENCE IS MEDIUM TO HIGH. THE LONG RANGE MODELS HAD BEEN CLOSING OFF A BIG UPPER LOW JUST TO OUR EAST/SOUTHEAST BY THE WEEKEND. THIS WOULD BRING CLOUDS AND PRECIP TO THE SOUTHEAST CWA FROM TIME TO TIME. THE ECMWF AND THE GEM /CANADIAN/ HAVE NOW BACKED OFF THAT SOLUTION IN FAVOR OF A MORE PROGRESSIVE OPEN WAVE. THE GFS WHICH HAD BEEN AN OPEN WAVE...NOW CREATES A CLOSED LOW. SIGH. THE BEST ODDS ARE WITH THE NEW ECMWF AND GEM. THIS WOULD PUT OUR AREA UNDER THE PROTECTION OF A VERY LARGE SCALE UPPER RIDGE...KEEPING IT DRY AND PLEASANT FROM THE WEEKEND INTO EARLY NEXT WEEK. I CAN/T GIVE UP ENTIRELY ON THE SMALL POPS IN THE SOUTHEAST YET AS THE MODELS DO HAVE A TENDENCY TO COME BACK TO THEIR ORIGINAL SOLUTIONS. BUT IF THIS PROGRESSIVE PATTERN HOLDS IN SUBSEQUENT RUNS...WE SHOULD BE ABLE TO PULL PRECIP MENTION DURING THIS PERIOD. && .AVIATION/00Z TAFS/... STILL THINK STORMS COULD FIRE ACROSS OR MOVE INTO THE WESTERN FORECAST AREA LATE THIS AFTERNOON AND EARLY EVENING...WITH A CHANCE LINGERING THROUGH THE NIGHT. SOME OF THE STORMS MAY BE SEVERE WITH LARGE HAIL AND DAMAGING WINDS THE MAIN THREAT. BETTER WIDESPREAD CHANCE FOR SHOWERS AND STORMS COMES TOMORROW AS THE MAIN SHORTWAVE AND COLD FRONT COME THROUGH. BACKED OFF ON LOWER VISIBILITIES IN THE TAFS FOR TONIGHT. WINDS WILL BE ON THE LIGHT SIDE...BUT POSSIBLE CLOUDS AND CONVECTION WOULD CERTAINLY DISRUPT FOG POTENTIAL. KIND OF A TOUGH CALL...AS VISIBILITIES MAY TANK QUICKLY IF SKIES CLEAR OUT GIVEN RECENT RAIN AND AMPLE LOW LEVEL MOISTURE. WILL HAVE TO KEEP A CLOSE EYE ON SATELLITE TRENDS AND ADJUST TAFS AS NEEDED. LOWER CIGS/VSBYS LIKELY AS USUAL WITHIN MODERATE TO HEAVY PRECIP. OTHERWISE...VFR CONDITIONS WILL PREVAIL THROUGH WEDNESDAY. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && TONIGHT/WEDNESDAY AND AVIATION/MARINE...DDV WEDNESDAY NIGHT THROUGH TUESDAY...DAVIS
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 345 PM CDT TUE SEP 4 2012 WIZ046-047-051-052-056>060-062>072-050945- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 345 PM CDT TUE SEP 4 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TONIGHT SCATTERED THUNDERSTORMS ARE EXPECTED TONIGHT...MAINLY WEST OF MADISON...AS LOW PRESSURE MOVES INTO NORTHWEST WISCONSIN AND WEAKENS. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEST OF A FOND DU LAC TO JANESVILLE LINE. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THUNDERSTORMS ARE LIKELY WEDNESDAY AS A STRONG COLD FRONT SWEEPS THROUGH THE AREA. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED WEDNESDAY. LMZ643>646-050945- SHEBOYGAN TO PORT WASHINGTON WI- PORT WASHINGTON TO NORTH POINT LIGHT WI- NORTH POINT LIGHT TO WIND POINT WI- WIND POINT WI TO WINTHROP HARBOR IL- 345 PM CDT TUE SEP 4 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...TODAY AND TONIGHT THERE IS A SLIGHT CHANCE OF THUNDERSTORMS TONIGHT. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY THUNDERSTORMS ARE LIKELY ON WEDNESDAY AS A COLD FRONT MOVES ACROSS LAKE MICHIGAN. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS. WWW.WEATHER.GOV/MKX
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 730 PM CDT TUE SEP 4 2012 WIZ062-063-067-068-050130- DANE-GREEN-IOWA-LAFAYETTE- 730 PM CDT TUE SEP 4 2012 ...STRONG THUNDERSTORM MOVING TOWARD SOUTHERN IOWA AND LAFAYETTE COUNTIES... AT 724 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A BROKEN LINE OF STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 34 MILES NORTHWEST OF DODGEVILLE TO 28 MILES WEST OF MINERAL POINT...MOVING SOUTHEAST AT 30 MPH. NICKEL SIZE HAIL...WINDS UP TO 50 MPH...FREQUENT CLOUD TO GROUND LIGHTNING...BRIEF HEAVY DOWNPOURS...ARE POSSIBLE WITH THESE STORMS. * THUNDERSTORMS WILL BE NEAR... BLACKHAWK LAKE RECREATION AREA BY 750 PM CDT... BELMONT BY 805 PM CDT... BENTON BY 810 PM CDT... MINERAL POINT AIRPORT BY 815 PM CDT... GOVERNOR DODGE STATE PARK AND MINERAL POINT BY 820 PM CDT... SHULLSBURG BY 825 PM CDT... DARLINGTON BY 830 PM CDT... IF THESE STORMS MAINTAIN THEIR CURRENT INTENSITY...THEN A SEVERE THUNDERSTORM WARNING MAY BE NEEDED FOR THESE AREAS BY 8 OR 830 PM CDT. GUSTY WINDS MAY CAUSE SMALL BRANCHES TO BE BLOWN DOWN...AND LOOSE OBJECTS TO BLOW AROUND. STAY AWAY FROM HIGH OBJECTS OUTDOORS SUCH AS TREES. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THESE STORMS HAVE PASSED. MBK
The La Crosse radar (KARX), 111 km away, was scanning. The volume nearest the first event began at 00:38 UTC.
26 thunderstorm wind, 1 hail. Local standard time, as filed.
Sauk County 911 Call Center personnel reported trees and power lines were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) along a path from 3 miles south of Rock Springs to 5 miles south-southwest of Baraboo.
Sauk County 911 Call Center personnel reported trees and power lines were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) along a path from 5 miles southeast of Baraboo to Merrimac.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) 4 miles south-southwest of Avoca.
Law enforcement officials reported trees and power lines were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) in an 8-mile wide swath from Harmony Grove to 5 miles east-southeast of Arlington.
Law enforcement officials reported trees and power lines were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) along a path from Edmund to Dodgeville.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) in an 5-mile wide swath from Portage to Pardeeville.
The public reported trees were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) 2 miles west of Sun Prairie.
The public reported large tree branches were blown down by damaging thunderstorm wind gusts estimated at 50 knots (60 mph) 1 mile northeast of Camp Randall Stadium in Madison.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated to be 56 knots (65 mph) along a path from New Glarus to 7 miles east of Dayton.
A HAM radio operator reported trees and large branches were blown down by damaging thunderstorm wind gusts estimated to be 56 knots (65 mph) 2 miles south-southwest of Stoughton.
The Jefferson County 911 Call Center reported trees and power lines were blown down by damaging thunderstorm wind gusts estimated to be 56 knots (64 mph) in Lake Mills.
A trained spotter reported trees were blown down by damaging thunderstorm wind gusts estimated to be 56 knots (64 mph) along a path from Evansville to 5 miles east-northeast of Milton.
A trained spotter reported trees and power lines blown down by damaging thunderstorm wind gusts estimated at 52 knots (60 mph) in Lowell.
A trained spotter reported trees were blown down by damaging thunderstorm wind gusts estimated to be 56 knots (65 mph) 1 mile northeast of Stoughton.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) 7 miles northeast of Darlington.
A trained spotter reported trees were blown down by damaging thunderstorm wind gusts estimated to be 52 knots (60 mph) 1 mile east of Fort Atkinson.
The Waukesha County 911 Center received reports of trees blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) from 5 miles northwest of Eagle to Eagle.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) in New Digging.
The Walworth County 911 Center received reports of trees blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) from La Grange to Delavan.
The Racine County 911 Call Center reported trees and power lines blown down by damaging thunderstorm wind gusts estimated at 56 knots (65 mph) from Tichigan to Burlington.
A trained spotter reported trees and power lines blown down by damaging thunderstorm wind gusts estimated at 52 knots (60 mph) in Wind Lake.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated at 52 knots (60 mph) along a Wheatland to Paris line.
Law enforcement officials reported trees were blown down by damaging thunderstorm wind gusts estimated at 50 knots (58 mph) in Fredonia.
Law enforcement officials reported were trees blown down by damaging thunderstorm wind gusts estimated at 60 mph (52 knots) 1.5 miles northeast of Benet Lake.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2012Every state in 2012This day in weather historyWarnings in Wisconsin, September 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: 414177, 414178, 414386, 414399, 414387, 414403, 414407, 414392, 414409, 414494, 414500, 414505, 414525, 414528, 414540, 414529, 414536, 414530, 414539, 414537, 414538, 414542, 414546, 414548, 414549, 414557, 414553.