Thunderstorms developed over western Wisconsin ahead of a cold front, with isolated thunderstorms becoming severe as they moved into South Central Wisconsin. The storms strengthened as they moved into a region of increased instability, with most-unstable CAPE up to 1000 J/kg and moderate effective shear.
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 over western Wisconsin ahead of a cold front, with isolated thunderstorms becoming severe as they moved into South Central Wisconsin. The storms strengthened as they moved into a region of increased instability, with most-unstable CAPE up to 1000 J/kg and moderate effective shear. The severe thunderstorms produced wind gusts up to 50 knots (58 mph) that downed trees in Marquette County, with strong thunderstorms producing nickel-sized hail near Brookfield in Waukesha County during the early morning hours of August 16th.
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 Aug 15, 8:21 PM CST, 5 hours 51 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 921 PM CDT WED AUG 15 2012 .UPDATE... LATEST 4 KM WRF MODEL RUNS STILL TAKE AN RATHER STRONG MCS ACROSS THE FORECAST AREA DURING THE EARLY MORNING HOURS. HOWEVER THIS IS ALL BASED ON PRE 00Z NEW UPPER AIR DATA. STILL 0-1 KM CAPE VALUES ARE AROUND 1600/2000 J/KG OVER SOUTHEAST MINNESOTA...SO THE STORMS ARE JUST NOW REACHING THE MOST UNSTABLE AIR. 00Z NAM MAX 0-1 KM CAPE VALUES DO DIMINISH DURING THE EARLY MORNING HOURS AS THE AXIS OF INSTABILITY PUSHES INTO SOUTH CENTRAL/SOUTHEAST WISCONSIN. 0-6 KM BULK SHEAR IS SLOW TO INCREASE...REACHING ONLY 35 KNOTS BY SUNRISE IN SOUTH CENTRAL WISCONSIN. THE INCREASING 250 MB JET MAX DOES NOT REACH SOUTHERN WISCONSIN UNTIL LATE MORNING/EARLY AFTERNOON. SPC DROPPED THE FORECAST FROM SLIGHT RISK OF SEVERE...THAT SEEMS REASONABLE. && .AVIATION/06Z TAFS/... MAINLY MID LEVEL CLOUDS AND ISOLATED SHOWERS UNTIL THE EARLY MORNING HOURS WHEN AN AREA OF THUNDERSTORMS SHOULD MOVE ACROSS SOUTHERN WISCONSIN ALONG AN APPROACHING COLD FRONT. VFR CONDITIONS EXCEPT SOME IFR IN THE LINE OF THUNDERSTORMS. SOME MVFR CIGS BEHIND THE FRONT THAT WILL RISE TO VFR BY AFTERNOON THURSDAY. && .PREV DISCUSSION... /ISSUED 228 PM CDT WED AUG 15 2012/ TONIGHT AND THURSDAY - CONFIDENCE...MEDIUM MAIN FOCUS IS ON INTENSITY OF COMPLEX AS IT ARRIVES INTO SRN WI LATER TONIGHT INTO THURSDAY MORNING. SOUTHWEST LOW LEVEL JET WILL INCREASE TO 30 TO 40 KNOTS WITH AN INCREASE IN MOISTURE INTO SRN WI. EXPECTING PREFRONTAL DEW POINTS TO CLIMB INTO THE LOW TO MID 60S. ELEVATED CAPES PER BUFKIT WILL BE IN THE 1000-1500 J/KG RANGE EVEN AT THIS UNFAVORABLE TIME FRAME. CWASP AGGREGATE SEVERE WEATHER PARAMETER NOT TOO SHABBY...WITH VALUES SHOWING A SPIKE OVER 60 PCT. DECENT UPPER JET DIVERGENCE WITH JET CORE ON EASTERN SIDE OF ADVANCING UPPER TROUGH. PRETTY GOOD FRONTOGENETICAL FORCING WITH SURFACE/850 FRONTS. MID LEVEL LAPSE RATES ABOVE 7C/KM. PARAMETERS SUGGESTING STORMS COULD MAINTAIN STRENGTH ACROSS CWA. 0-6KM SHEAR TO 40 KNOTS IN WESTERN CWA. 4KM NAM LOOKS MOST IMPRESSIVE FOR SRN WI WITH STORMS SWEEPING IN FROM ERN MN. NMM/ARW SUGGESTING A WEAKENING LOOK TO THE CONVECTION WHILE OTHER MODELS QPF SUGGESTS MAINTAINING THE STRENGTH ALL THE WAY ACROSS SRN WI. 4KM SPC WRF TAKES BETTER ACTION ACROSS NRN IL FEEDING ON BETTER CAPE AIR AND THIS SECOND MORE SOUTHERN COMPLEX IS SHOWN BY OTHER MODELS TOO WHICH COULD FEED OFF THE BETTER INSTABILITY PARAMETERS TO THE SOUTH. POTENTIALLY A CASE WHERE OUR CWA SEES BEST DYNAMICS NORTH AND BEST INSTABILITY SOUTH AND WE GET A LITTLE OF BOTH TO MAINTAIN STORMS WITH LIMITED SEVERE POTENTIAL. HIGH CONFIDENCE IN POPS BUT LOW CONFIDENCE ON HOW WIDESPREAD SEVERE RISK ENDS UP BEING AT THIS POINT. SPC HAS ADJUSTED THE DAY1 SLIGHT RISK A BIT FARTHER EAST...SO IF THE HIGHER CAPE AIR CAN GET DRAWN FURTHER NORTH...THE SEVERE THREAT COULD BE BETTER MAINTAINED LONGER AND FURTHER EAST IN SRN WI...AND THIS SCENARIO IS ALSO SUPPORTED BY 4SM NSSL WRF. HOPEFULLY ALL WILL AT LEAST GET A GOOD DRINK. THURSDAY NIGHT THROUGH SATURDAY NIGHT...FORECAST CONFIDENCE MEDIUM TO HIGH. CANADIAN HIGH PRESSURE WILL SETTLE IN BEHIND THE DEPARTING COLD FRONT THURSDAY NIGHT AND FRIDAY...THEN LINGER INTO THE WEEKEND. LATE SUMMER/EARLY FALL-LIKE TEMPERATURES WILL PUSH IN...ALONG WITH MORE DRY WEATHER. LOOK FOR HIGHS IN THE LOWER TO MID 70S WITH LOWS IN THE UPPER 40S TO LOWER 50S. SUNDAY AND BEYOND...FORECAST CONFIDENCE IS MEDIUM. NOTHING MAJOR SHOWING UP IN THE LONGER RANGE. A VERY LARGE UPPER LOW IS CENTERED OVER SOUTHERN HUDSON BAY SUNDAY THROUGH ABOUT TUESDAY. WE COULD SEE A FEW REINFORCING SHOTS OF COOL AIR BEHIND PERIODIC WEAK COLD FRONTS. SOME LIGHT SHOWERS ARE POSSIBLE...BUT TIMING OF THESE IS HIGHLY DIFFICULT AT THIS POINT. WE COULD EVEN SEE SOME LAKE EFFECT SHOWERS ON SUNDAY WITH DELTA T/S CLIMBING TO ABOUT 15C WITH AN ONSHORE FLOW POSSIBLE. AVIATION/00Z TAFS/...VFR CONDITIONS UNTIL LATER TONIGHT WHEN CONVECTIVE COMPLEX TAKES AIM ON SRN WI FROM MN/IA. INTENSITY OF STORMS NOT COMPLETELY CLEAR AT THIS POINT BUT WINDOW OF BEST POTENTIAL LOOKS TO BE 09-16Z ACROSS SRN WI. POTENTIAL FOR A PERIOD OF MVFR CEILINGS/VSBYS WITH CONVECTION AND FOR A TIME BEHIND THE FRONT WITH HIGHER LOW LEVEL MOISTURE. CONDITIONS LOOK TO RETURN TO VFR BY THURSDAY AFTERNOON. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && UPDATE...HENTZ TONIGHT/THURSDAY AND AVIATION/MARINE...COLLAR THURSDAY NIGHT THROUGH WEDNESDAY...DAVIS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 1139 PM CDT WED AUG 15 2012 WIZ046-047-051-052-056>060-062>072-170445- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 1139 PM CDT WED AUG 15 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TONIGHT A LINE OF THUNDERSTORMS ALONG A COLD FRONT IS EXPECTED TO REACH PORTIONS OF SOUTH CENTRAL WISCONSIN AROUND 3 AM...AND PORTIONS OF THE SOUTHEAST AROUND 5 AM. A FEW STORMS MAY APPROACH SEVERE LIMITS. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH WEDNESDAY THUNDERSTORMS ARE EXPECTED MAINLY THURSDAY MORNING AS THE COLD FRONT MOVES THROUGH. SOME OF THE THUNDERSTORMS MAY STILL BE STRONG. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME. LMZ643>646-170445- 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- 1139 PM CDT WED AUG 15 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...TONIGHT THERE IS A CHANCE FOR THUNDERSTORMS LATE TONIGHT AS A COLD FRONT APPROACHES FROM THE WEST. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH WEDNESDAY THUNDERSTORMS ARE EXPECTED MAINLY THURSDAY MORNING AS THE COLD FRONT MOVES THROUGH. SOME OF THE THUNDERSTORMS MAY STILL BE STRONG. GUSTY NORTHWEST WINDS MAY REACH SMALL CRAFT CRITERIA ON THURSDAY. HENTZ WWW.WEATHER.GOV/MKX
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 308 AM CDT THU AUG 16 2012 WIZ046-160915- MARQUETTE- 308 AM CDT THU AUG 16 2012 ...STRONG THUNDERSTORM MOVING INTO MARQUETTE COUNTY... AT 306 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER SOUTHWESTERN ADAMS COUNTY...MOVING EAST AT 35 MPH. NICKEL SIZE HAIL...WINDS UP TO 50 MPH...FREQUENT CLOUD TO GROUND LIGHTNING...BRIEF HEAVY DOWNPOURS...ARE POSSIBLE WITH THIS STORM. * THE THUNDERSTORM WILL BE NEAR... WESTFIELD BY 335 AM CDT... MONTELLO BY 350 AM 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 THIS STORM HAS PASSED. GEHRING
The national radar mosaic for the moment the first event began.
1 thunderstorm wind, 1 hail. Local standard time, as filed.
Law enforcement officials reported a tree down across a road in Westfield Township, blown down by thunderstorm wind gusts estimated up to 50 knots (58 mph). There were other nearby reports of large broken tree branches or knocked-over trees.
A trained spotter reported nickel-sized hail (0.88 inch in diameter) near the intersection of Interstate 94 and Moorland Road in Brookfield.
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, 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: 407782, 407783.