A strengthening low-level jet pushed over a stalled frontal boundary over southern Wisconsin with a very warm, moist and unstable air mass under very steep lapse rates provided the focus for strong to severe thunderstorms during the pre-dawn hours of July 24th. The severe thunderstorms produced a discontinous swath of damaging wind gusts that downed trees and power lines from near Darlington in…
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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.
A strengthening low-level jet pushed over a stalled frontal boundary over southern Wisconsin with a very warm, moist and unstable air mass under very steep lapse rates provided the focus for strong to severe thunderstorms during the pre-dawn hours of July 24th. The severe thunderstorms produced a discontinous swath of damaging wind gusts that downed trees and power lines from near Darlington in Lafayette County, eastward across Green and Rock counties to Lake Geneva in Walworth 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 Milwaukee, WI wrote its last area forecast discussion before the first event at Jul 24, 2:39 AM CST, 6 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 339 AM CDT TUE JUL 24 2012 .TODAY AND TONIGHT...FORECAST CONFIDENCE...MEDIUM DIMINISHING TREND NOTED IN CONVECTION OVER SOUTHWEST WI OVER LAST HOUR OR SO. SCATTERED TO NUMEROUS CONVECTION EXTENDS WELL TO THE WEST ACROSS SOUTHERN MN INTO EASTERN SODAK. HOWEVER FRONTAL BOUNDARY SAGGING ACROSS SOUTHERN WI ATTM...WL CONTINUE INTO NRN IL EARLY THIS MRNG. THIS WILL TIGHTEN THE BAROCLINICITY ACROSS SOUTHERN WI AND INCREASE THE LOW LEVEL FN VECTOR RESPONSE TO FRONTOGENESIS. THIS SHOULD HELP CONTINUE THE SCATTERED TO NUMEROUS CONVECTION OVER PORTIONS OF SOUTHERN WISCONSIN THROUGH MID-MORNING BEFORE DIMINISHING. PWAT VALUES IN THE 1.75 TO 2.0 INCH RANGE...WHICH IS ABOUT 160 PERCENT OF NORMAL. BOTH THE RAP AND NAM40KM SHOW LAYER FWF LINGERING OVER SOUTH CENTRAL WI TO AROUND 15Z BEFORE DIMINISHING. HENCE WL CONTINUE LIKELY WORDING IN THE SOUTH CENTRAL AREAS...DIMINISHING TO CHC/SCT IN THE NORTHEAST. UPSTREAM SHORT WAVE OVER ERN SODAK IS EXPECTED TO MOVE ESE ACROSS SRN MN INTO SRN WI LATER THIS MRNG...SO WL CONTINUE CHANCE INTO THE LATE MORNING. SHORT WAVE AND FRONTOGENETICAL FORCING WEAKENS AND SLIDES SOUTHEAST FOR THE AFTN. STRONG SURGE OF RETURN FLOW AND LOW LEVEL THETA-E ADVECTION ACCOMPANY DEVELOPING LOW LEVEL JET TONIGHT. FOCUS OF LLJ TO THE NORTHWEST OF CWA...HOWEVER STILL GET CLIPPED BY INCREASING WARM AIR ADVECTION. HENCE WL CONTINUE LIKELY POPS IN THE NORTH TONIGHT. .WEDNESDAY AND THURSDAY...FORECAST CONFIDENCE...MEDIUM CONVECTION NEAR WARM FRONT SHOULD WIND DOWN WEDNESDAY MORNING ACROSS THE NORTHERN FORECAST AREA. WARM FRONT THEN EXPECTED TO LINGER JUST NORTH OF THE CWA THROUGH THE DAY. MODELS INDICATING THAT TEMPS WILL SOAR IN THE WARM SECTOR...WITH 925 MB TEMPS UP TO AROUND 32C ON THE ECMWF AND EVEN WARMER WITH THE NAM. CONCERN IS CERTAINLY THERE THAT OVERNIGHT CONVECTION MAY KEEP THE WARM FRONT FARTHER SOUTH...AND THEN ALSO PULL IN COOLER AIR OFF THE LAKE NORTH OFF THE FRONT. FOR NOW THOUGH...WENT WITH WHAT THE MODELS ARE SHOWING AND BUMPED TEMPS UP TO AROUND 100 MOST PLACES...EXCEPT FOR IN THE NORTH TOWARD THE WARM FRONT. TOO MUCH UNCERTAINTY WITH LINGERING CONVECTION/CLOUDS AND PLACEMENT OF THE WARM FRONT...SO HELD OFF ON HEAT ADVISORY FOR NOW. WILL EVENTUALLY NEED ONE IF MODELS CONTINUE DOWN THIS ROAD AND FORECAST CONFIDENCE INCREASES. EVEN WITH DEWPOINTS MIXING INTO THE MID AND UPPER 60S...TEMPS AROUND 100 WOULD RESULT IN HEAT INDICES IN THE 100-105 RANGE. CONVECTION WITH THE TRAILING COLD FRONT IS EXPECTED TO MAINLY HOLD OFF UNTIL THE EVENING AND OVERNIGHT HOURS. WITH 30 KT LLJ ACROSS THE AREA AND CAPES IN EXCESS OF 1000 J/KG...STILL THINKING STORMS SEVERE STORMS ARE A POSSIBILITY AND SPC IS MAINTAINING A SLIGHT RISK. KEPT SOME POPS THURSDAY MORNING...AS THE ECMWF LINGERS POST FRONTAL PRECIP. OTHERWISE...SHOULD MAINLY BE DRY THURSDAY. A WEAK WAVE MAY BRING A FEW MORE SHOWERS/STORMS TO THE AREA LATER IN THE DAY AND OVERNIGHT. THINKING THE SUN MAY POKE OUT FOR A TIME THURSDAY...SO PUSHED HIGHS UP INTO THE MID AND UPPER 80S PER 925 MB TEMPS IN THE 22-25C RANGE. .FRIDAY AND SATURDAY...FORECAST CONFIDENCE...MEDIUM PRECIP MAY LINGER INTO FRIDAY MORNING AS THE SHORTWAVE EXITS...WITH DRY WEATHER EXPECTED SATURDAY AS SFC HIGH PRESSURE MOVES OVERHEAD. SHOULD SEE HIGHS COMFORTABLY NEAR NORMAL BOTH DAYS. .SUNDAY AND MONDAY...FORECAST CONFIDENCE...MEDIUM WITH UPPER RIDGE BUILDING IN TO THE WEST SUNDAY AND MONDAY...COMBINATION OF WARM AIR ADVECTION AND A WEAK WAVE OR TWO MAY KICK OFF SHOWERS/STORMS AT TIMES. WILL LIKELY SEE TEMPS START TO WARM BACK UP. && .AVIATION/12Z TAFS/...SCATTERED TO NUMEROUS CONVECTION LIKELY THIS MORNING WITH MOST NUMEROUS CONVECTION TOWARDS KMSN. ENOUGH RAINFALL TO MOISTEN LOW LEVELS EXPECTED TO PRODUCE PERIOD OF MVFR CIGS AT KMSN. NOT AS CONFIDENT ON LOW CIGS FARTHER EAST WHERE RAINFALL MAY BE A BIT MORE SCATTERED. MAY USE A TEMPO GROUP WITH 12Z ISSUANCE. ANY LOWER CIGS SHOULD LIFT TO VFR THIS AFTN AS FORCING SLIDES SOUTH OF AREA AND SLIGHTLY DRIER AIR GETS PULLED INTO THE LOWER LEVELS. MORE SCT CONVECTION TONIGHT WITH STRONG RETURN FLOW. && .MARINE...ONE TO TWO HOURS OF GUSTY NORTHEAST WINDS ACCOMPANIED FROPA AS IT MOVED SOUTH ALONG THE LAKE MICHIGAN SHORE EARLY THIS MORNING. THE FRONT WILL CONTINUE SAGGING SOUTHWARD WITH NORTHEAST WINDS SETTLING DOWN TO 5 TO 15 KNOTS. SCATTERED T TO AFFECT NEAR SHORE WATERS THIS MORNING AND AGAIN LATER TNGT. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && TODAY/TONIGHT AND AVIATION/MARINE...MBK WEDNESDAY THROUGH MONDAY...DDV
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 810 PM CDT MON JUL 23 2012 WIZ046-047-051-052-056>060-062>072-240900- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 810 PM CDT MON JUL 23 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TONIGHT THERE IS A CHANCE OF THUNDERSTORMS LATE THIS EVENING AND DURING THE OVERNIGHT...WITH THUNDERSTORMS BECOMING LIKELY LATE TONIGHT WEST AND SOUTH OF MADISON. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY HEAT INDEX VALUES COULD REACH THE 95 TO 105 DEGREE RANGE ON WEDNESDAY...MAINLY SOUTH OF A MONTELLO TO MILWAUKEE LINE...AS SOUTHWEST WINDS BRING HOT AIR BACK INTO THE AREA. A HEAT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE AREA ON WEDNESDAY. THERE WILL BE THUNDERSTORMS FROM TIME TO TIME TUESDAY THROUGH FRIDAY...AS A FRONTAL BOUNDARY LINGERS NEAR OR ACROSS THE AREA...ALONG WITH A SOMEWHAT FAST UPPER LEVEL ATMOSPHERIC FLOW ACROSS THE NORTHERN UNITED STATES. ONE OF THE BETTER CHANCES FOR STORMS WILL BE TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...AS A WARM FRONT PUSHES THROUGH THE AREA. THERE A SLIGHT RISK OF SEVERE STORMS TUESDAY AND TUESDAY NIGHT WEST OF A LONE ROCK TO DARLINGTON LINE...AND WEDNESDAY AND WEDNESDAY NIGHT ACROSS THE ENTIRE AREA. LARGE HAIL AND DAMAGING WINDS WOULD BE THE PRIMARY HAZARDS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED AT TIMES THROUGH WEDNESDAY NIGHT. LMZ643>646-240900- 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- 810 PM CDT MON JUL 23 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...TONIGHT THERE IS A CHANCE OF THUNDERSTORMS LATE TONIGHT AS A WEAK COLD FRONT MOVES SOUTH ACROSS WISCONSIN AND LAKE MICHIGAN. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY THERE WILL BE THUNDERSTORMS FROM TIME TO TIME TUESDAY THROUGH FRIDAY...AS A FRONTAL BOUNDARY LINGERS NEAR OR ACROSS THE AREA...ALONG WITH A SOMEWHAT FAST UPPER LEVEL ATMOSPHERIC FLOW ACROSS THE NORTHERN UNITED STATES. ONE OF THE BETTER CHANCES FOR STORMS WILL BE TUESDAY NIGHT THROUGH WEDNESDAY NIGHT...AS A WARM FRONT PUSHES THROUGH THE AREA. THERE A SLIGHT RISK OF SEVERE STORMS WEDNESDAY AND WEDNESDAY NIGHT ACROSS THE NEARSHORE WATERS. LARGE HAIL AND DAMAGING WINDS WOULD BE THE PRIMARY HAZARDS. GEHRING WWW.WEATHER.GOV/MKX
The La Crosse radar (KARX), 98 km away, was scanning. The volume nearest the first event began at 08:44 UTC.
11 thunderstorm wind. Local standard time, as filed.
Law enforcement reported trees were blown down by severe thunderstorm wind gusts estimated at 56 knots (64 mph).
Law enforcement reported trees and power lines were blown down by severe thunderstorm wind gusts estimated at 56 knots (64 mph).
Law enforcement reported trees and power lines were blown down by severe thunderstorm wind gusts estimated at 56 knots (64 mph).
Emergency management officials reported trees and numerous power lines were blown down throughout the county by severe thunderstorm wind gusts estimated at 56 knots (64 mph). A window at a car dealership in Monroe was blown out by the damaging winds.
Law enforcement officials reported trees and power lines were blown down in a swath from Gratiot to South Wayne by severe thunderstorm wind gusts estimated at 56 knots (64 mph).
A trained spotter reported trees and power lines were blown down by severe thunderstorm wind gusts estimated at 56 knots (64 mph). Heavy rains also caused a rain gutter to back up with water covering State Highway 69 in Monroe.
A trained spotter measured a severe thunderstorm wind gust estimated at 52 knots (60 mph).
Law enforcement officials reported trees and power lines were blown down by severe thunderstorm wind gusts estimated at 61 knots (70 mph).
A local newspaper reported trees and power lines were blown down all over the county by severe thunderstorm wind gusts estimated at 65 knots (75 mph). The fallen trees blocked roads in residential neighborhoods on the west side of Beloit, as well as on State Highway 213 between Luther Valley Road and Yahara Road. Homes and vehicles were damaged by storm debris. It was estimated 7,000 people were without power. A residential fire on Lincoln Avenue in Beloit was possibly started by lightning.
Law enforcement officials reported trees were blown down by severe thunderstorm wind gusts estimated at 56 knots (65 mph).
Law enforcement officials reported scattered trees and a power pole were blown down by severe thunderstorm wind gusts estimated at 56 knots (65 mph) in a swath from 3 miles southwest of Lake Geneva to Lake Geneva.
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, July 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: 404681, 404682, 404683, 404685, 404687, 404689, 404690, 404691, 404692, 404693, 404694.