A short wave moving up the leading flank of an elongated large-scale trough that extended from the Upper Mississippi River Valley to the Central Plains provided large-scale lift for thunderstorm development over southern Wisconsin. A warm front extended across central Wisconsin back to surface low pressure over west-central Minnesota.
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.
A short wave moving up the leading flank of an elongated large-scale trough that extended from the Upper Mississippi River Valley to the Central Plains provided large-scale lift for thunderstorm development over southern Wisconsin. A warm front extended across central Wisconsin back to surface low pressure over west-central Minnesota. This placed southern Wisconsin in a warm humid air mass, with temperatures in the 80's and dew points in the lower 70's producing CAPE values reaching 2000 J/kg. Deep-layer shear profiles were favorable for supercells as well as multicell line segments that produced damaging wind gusts. The thunderstorm winds caused widespread tree and power line damage. WE energies reported 23,000 customers were without power.
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 20, 12:39 PM CST, 1 hour 28 minutes earlier.
AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 139 PM CDT FRI AUG 20 2010 .UPDATE... LATEST RUC SOUNDINGS KEEPS VEERING WIND PROFILE IN THE LOW LEVELS A BIT LONGER. THIS PROLONGS THE SUPER CELL POTENTIAL OVER SOUTH EAST AND ESPECIALLY SOUTH CENTRAL WISCONSIN INTO THE EVENING. EHI AT NEAR 3 AT MKE AND MSN AT 22Z AND 23Z...AND STILL 1.5 TO 2.0 AT 03Z. BULK RICHARDSON NUMBERS BETWEEN 35 AT 45. CAP AT 900 MB APPEARS TO WEAKEN AND BREAKS BY 20Z. LATEST 4 KM 15Z WRF DEVELOPS DEEP CONVECTION AFTER 00Z IN A LINE FROM NEAR OSHKOSH TO MADISON TO LAFAYETTE COUNTY. MODEL KEEPS CELLS FAIRLY DISCRETE WITH AROUND 5 OR 6 SEPARATE STORMS. THE LATEST HIGH RES RAPID REFRESH BRINGS THUNDERSTORMS NOW OVER NORTHWEST ILLINOIS INTO SOUTH CENTRAL WISCONSIN AROUND 21Z. APPEARS SEVERE WEATHER THREAT REMAINS WITH PARAMETERS INCREASING FOR SEVERE POTENTIAL LATE THIS AFTERNOON AND THIS EVENING. && .PREV DISCUSSION... /ISSUED 1125 AM CDT FRI AUG 20 2010/ SHORT TERM... LATE THIS AFTERNOON AND TONIGHT...FORECAST CONFIDENCE MEDIUM. WARM FRONT ACROSS CENTRAL WISCONSIN WILL PUSH NORTH ACROSS NORTHERN WISCONSIN AND THE U.P. BY EVENING. WEAK SURFACE TROUGH ACROSS MINNESOTA TO KANSAS ASSOCIATED WITH MID LEVEL SHORTWAVE OVER THE PLAINS. THE SURFACE TROUGH WILL PUSH ACROSS MUCH OF WISCONSIN AND WESTERN ILLINOIS OVERNIGHT AS THE PLAINS SHORTWAVE MOVES EAST. THE 12Z NAM SPLITS THE SHORTWAVE WITH ONE TROUGH MOVING ACROSS WESTERN LAKE SUPERIOR AND A SOUTHERN ONE EXITING EASTERN COLORADO THE NORTHERN THIS EVENING. ZERO TO 6 KM SHEAR NOW AROUND 40 TO 45 KNOTS THEN WEAKENS BY EVENING TO AROUND 35 KNOTS. TORNADO PARAMETERS WILL BE GREATEST LATE THIS AFTERNOON. AFTERNOON NAM SURFACE BASED CAPE FROM 3000 TO 4000 J/KG. CAP AROUND 900 MB WEAKENS BY MID AFTERNOON ON BOTH RUC AND NAM SOUNDING. HELICITY NEAR 200 OVER EASTERN SECTIONS OF THE FORECAST AREA BUT LOWER TO THE WEST OVER SOUTH CENTRAL WISCONSIN. RUC SHOWS EHI AROUND 3 IN THE SOUTHEAST BUT A LITTLE LOWER WITH AROUND 1.5 OVER SOUTH CENTRAL WISCONSIN. BULK RICHARDSON NUMBER AROUND 35 OVER SOUTHEAST WISCONSIN BY EVENING...BUT MAINLY IN THE 70S OVER SOUTH CENTRAL WISCONSIN. LOW LEVEL WINDS VEER OVER SOUTH CENTRAL WISCONSIN THIS AFTERNOON AND OVER SOUTHEAST WISCONSIN DURING THE EVENING. THEREFORE ANY THUNDERSTORMS THAT DEVELOP IN THE EARLY AFTERNOON WILL HAVE SUPER CELL TENDENCIES OVER SOUTH CENTRAL WISCONSIN...WITH SUPER CELL POTENTIAL INTO THE EARLY EVENING OVER THE SOUTHEAST. IT APPEARS MAIN TRIGGER...THE SHORTWAVE...WILL INCREASE UPWARD MOTION JUST AS THE SUPER CELL THREAT STARTS TO DIMINISH. HOWEVER THERE DOES APPEAR TO BE SOME POTENTIAL FOR THESE TO OVERLAP...ESPECIALLY OVER THE SOUTHEAST. IN OTHER WORDS THE QUICKER ANY DEEP CONVECTION DEVELOPS...THE MORE LIKELY IT WILL BE SEVERE. SPC KEEPS MAIN TORNADO THREAT AREA TO THE NORTH OF THE FORECAST AREA CLOSER TO THE WARM FRONT...ALTHOUGH WE ARE IN THE 2 PCT PROBABILITY AREA. NAM SHOWS QPF DEVELOPING AFTER 21Z AND CONTINUING DURING THE EVENING. AFTER MIDNIGHT MOST CONVECTION WAS OVER SOUTHEAST WISCONSIN AND ALONG THE ILLINOIS BORDER IN SOUTH CENTRAL WISCONSIN. SOME HEAVY RAINFALL POSSIBLE WITH PRECIPITABLE WATER VALUES NEAR 2 INCHES AND RATHER SLOW MOVEMENT OF THE STORMS. CORFIDI VECTORS TONIGHT ARE GENERALLY LESS THAN 10 KNOTS. SATURDAY...FORECAST CONFIDENCE MEDIUM. 700 MB LOW IS OVER SOUTHEAST TIP OF WISCONSIN SATURDAY MORNING WITH BEST LIFT OVER SOUTHERN LAKE MICHIGAN. CORFIDI VECTORS REMAIN WEAK AT 10 KNOTS OR LESS. THIS WILL BRING HIGH QPF POTENTIAL VERY CLOSE TO THE SOUTHEAST TIP OF THE FORECAST AREA...WITH THE KENOSHA FORECAST SOUNDING SATURATED BELOW 500 MB. NAM SURFACE LOW MOVES ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN. WILL HAVE TO WATCH FOR A POTENTIAL SHARS RAINFALL EVENT...ALTHOUGH 700 MB WINDS MAY BE TO WESTERLY FOR A CLASSIC SOUNDING PROFILE. 12Z NAM SOUNDING SHOW 1500 J/KG RESIDUAL SURFACE BASED CAPE EVEN OVER SOUTH CENTRAL WISCONSIN...SO LINGERING SHOWERS STILL POSSIBLE...ALTHOUGH MID LEVEL DRYING IS STRONG...AND A CAP DOES DEVELOP BY MID AFTERNOON OVER SOUTH CENTRAL WISCONSIN. GFS BRINGS MORE QPF BACK WEST THAN NAM. MET/MAV MOS GUIDANCE STILL BELOW 20 PERCENT...SO MAY STILL LEAVE THE FORECAST DRY FOR THE AFTERNOON. SUNDAY AND MONDAY...FORECAST CONFIDENCE HIGH. SHORTWAVE EXITS THE EASTERN GREAT LAKES AS UPPER LEVEL RIDGE BUILDS OVER THE UPPER MISSISSIPPI VALLEY AND WISCONSIN REGION AS HIGH PRESSURE EXTENDS ACROSS THE GREAT LAKES REGION. LONG TERM... TUESDAY THROUGH THURSDAY...FORECAST CONFIDENCE MEDIUM A RATHER STRONG SHORTWAVE PUSHES ACROSS SOUTH CENTRAL WISCONSIN WITH A TRAILING COLD FRONT PUSHING ACROSS THE FORECAST AREA TUESDAY. QPF IS RATHER LIGHT...BUT 12Z GFS AND 00Z ECMWF DOES BRING FROM 0.05 TO 0.10 INCH OF QPF. THIS AND THE RATHER STRONG SHORTWAVE LENDS TO AN INCREASE IN POPS INTO THE LOWER CHANCE CATEGORY AND MENTION OF SOME THUNDERSTORM POTENTIAL. WEDNESDAY THROUGH FRIDAY...FORECAST CONFIDENCE MEDIUM UPPER RIDGE BUILDS ACROSS THE UPPER MISSISSIPPI VALLEY AND PUSHES INTO WISCONSIN FRIDAY. THIS BRINGS COOLER AND LESS HUMID AIR INTO THE AREA. && .MARINE... GUSTY SOUTH WINDS WILL CONTINUE UNTIL EARLY EVENING ACROSS KMSN AND KUES. LAKE BREEZE SHOULD REACH KMKE AND KENW DURING THE EARLY AFTERNOON AND LIMIT GUSTS. MAIN ISSUE IS DEALING WITH THUNDERSTORMS FOR TONIGHT. WENT WITH VICINITY THUNDER IN TAFS AFTER 22Z TO 23Z FRIDAY GIVEN SOME UNCERTAINTY WITH TIMING OF STORMS INTO THE AREA. EXPECT BROKEN LINE OF STORMS TO REACH KMSN AFTER 00Z SATURDAY AT KMSN...AND AFTER 01Z TO 02Z AT THE EASTERN TAF SITES. THE STORMS SHOULD CONTINUE ON AND OFF THROUGH AT LEAST 07Z TO 08Z SATURDAY AT KMSN...AND UNTIL 11Z TO 12Z SATURDAY AT THE EASTERN TAF SITES. WENT WITH PREVAILING VFR TO MVFR VISIBILITIES...AND VFR CEILINGS...WITH THE THUNDERSTORMS. IFR VISIBILITIES ARE POSSIBLE AT TIMES. LEFT THUNDER IN PREVAILING GROUP UNTIL MID MORNING SATURDAY FOR ANY LINGERING STORMS IN THE AREA. PRECIPITATION SHOULD THEN GRADUALLY END BY LATE MORNING...WITH WINDS SHIFTING AROUND TO THE NORTHEAST AND NORTH. SCATTERED TO BROKEN CUMULUS THEN EXPECTED THROUGH THE REST OF SATURDAY. && .MARINE...TIGHT SURFACE PRESSURE GRADIENT AND GOOD LOW LEVEL MIXING MAY ALLOW FOR SOME GUSTS TO NEAR 22 KNOTS AT TIMES THROUGH EARLY THIS EVENING ACROSS THE NEARSHORE WATERS. AT THIS TIME...DO NOT THINK THEY WILL BE FREQUENT OR WIDESPREAD ENOUGH FOR A SMALL CRAFT ADVISORY. GOOD MIXING AND A TIGHT PRESSURE GRADIENT MAY ALLOW FOR WINDS TO FREQUENTLY GUST TO NEAR 22 KNOTS AGAIN LATE SATURDAY NIGHT AND SUNDAY ACROSS THE NEARSHORE WATERS. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && SHORT/LONG TERM...06/HENTZ AVIATION/MARINE...08/WOOD
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 230 PM CDT FRI AUG 20 2010 WIZ046-047-051-052-056>060-062>072-211000- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 230 PM CDT FRI AUG 20 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...THIS AFTERNOON AND TONIGHT THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND TONIGHT...AS AN UPPER LEVEL DISTURBANCE MOVES THROUGH. SOME OF THE STORMS ARE EXPECTED TO BECOME SEVERE WITH DAMAGING WINDS THE MAIN THREAT. LOCALLY HEAVY RAINS ARE POSSIBLE SD WELL. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY THERE IS A CHANCE OF THUNDERSTORMS FOR SOUTHEAST WISCONSIN...WITH A SLIGHT CHANCE OF THUNDERSTORMS IN SOUTH CENTRAL WISCONSIN SATURDAY MORNING. THERE IS A SLIGHT CHANCE OF THUNDERSTORMS FOR ALL OF SOUTHERN WISCONSIN TUESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NEEDED THIS AFTERNOON AND EVENING. RAINFALL REPORTS ARE ALSO NEEDED. LMZ643>646-211000- 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- 230 PM CDT FRI AUG 20 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...THIS AFTERNOON AND TONIGHT THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND TONIGHT. SOME OF THE STORMS ARE EXPECTED TO BECOME SEVERE WITH DAMAGING WINDS THE MAIN THREAT. WINDS AND WAVES WILL APPROACH SMALL CRAFT CRITERIA THIS AFTERNOON. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY WINDS AND WAVES WILL APPROACH SMALL CRAFT CRITERIA SUNDAY. THERE IS A CHANCE OF THUNDERSTORMS SATURDAY MORNING. THERE IS A SLIGHT CHANCE OF THUNDERSTORMS TUESDAY. KAPELA WWW.WEATHER.GOV/MKX
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 251 PM CDT FRI AUG 20 2010 WIZ047-202045- GREEN LAKE- 251 PM CDT FRI AUG 20 2010 ...STRONG THUNDERSTORM MOVING THROUGH GREEN LAKE COUNTY... AT 248 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A STRONG THUNDERSTORM 8 MILES SOUTHWEST OF BERLIN...MOVING NORTHEAST AT 45 MPH. ONE HALF INCH DIAMETER HAIL...WINDS GREATER THAN 40 MPH...BRIEF HEAVY DOWNPOURS...ARE POSSIBLE WITH THIS STORM. * THE THUNDERSTORM WILL BE NEAR... BERLIN BY 300 PM CDT... GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW AROUND. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THIS STORM HAS PASSED. ZABEL
The Green Bay radar (KGRB), 93 km away, was scanning. The volume nearest the first event began at 20:05 UTC.
29 thunderstorm wind. Local standard time, as filed.
County officials reported a tree fell through a house in Berlin. Power lines were reported down by the strong thunderstorm gusts, as well as minor crop damage.
County sheriff deputies reported trees and power lines were blown down by the strong thunderstorm gusts.
County sheriff deputies reported trees and power lines were blown down by the strong thunderstorm gusts. The AWOS at Janesville airport recorded a 58 mph (50 knot) wind gust at 345 pm CDT.
County sheriff deputies reported trees were blown down in and around the city of Whitewater to just west of Palmyra by the strong thunderstorm gusts. The damage was produced by three separate storms that trained over the area. There was also urban flooding in Whitewater and Palmyra caused by 2 inches of rain that fell in 45 minutes.
County sheriff deputies reported trees and power lines were blown down by the strong thunderstorm gusts.
County sheriff deputies reported trees were blown down by the strong thunderstorm gusts.
County sheriff deputies reported trees were blown down by the strong thunderstorm gusts.
County sheriff deputies reported trees were blown down by the strong thunderstorm gusts.
County sheriff deputies reported trees were blown down by the strong thunderstorm gusts.
The peak thunderstorm wind gust of 58 mph (50 knots) measured at the National Weather Service office southeast of Sullivan.
County sheriff deputies reported trees were blown down in the Lowell area by the strong thunderstorm gusts.
The peak thunderstorm wind gust of 61 mph (53 knots) was measured at a mesonet site in Slinger.
County sheriff deputies reported trees were blown down by the strong thunderstorm gusts.
County Sheriff deputies reported tree damage due to thunderstorm wind gusts along a path from Oostburg to the city of Sheboygan. The Sheboygan C-MAN observation site at the harbor recorded a 49 knot (56 mph) wind gust at 5 pm CDT.
The peak thunderstorm wind gust of 65 mph (56 knots) measured by a trained spotter.
The peak thunderstorm wind gust of 74 mph (64 knots) was measured by a trained spotter in West Bend.
An amateur radio operator reported tree damage and power lines blown down onto a home in Oxford by thunderstorm wind gusts estimated at 56 knots (65 mph).
Law enforcement officials reported a 100-year old barn was blown down by thunderstorm wind gusts estimated at 50 knots (58 mph).
The Columbia County emergency manager reported tree damage caused by thunderstorm wind gusts estimated at 56 knots (65 mph).
Fire officials reported tree damage by thunderstorm wind gusts estimated at 56 knots (65 mph).
The Green Lake County emergency manager reported tree damage caused by thunderstorm wind gusts estimated at 56 knots (65 mph).
Law enforcement officials reported shingles blown off a home and tree damage by thunderstorm wind gusts estimated at 70 knots (81 mph).
Fire officials reported tree damage by thunderstorm wind gusts estimated at 56 knots (65 mph).
The Walworth County Emergency Manager reported a pole barn was partially damaged by thunderstorm winds estimated at 50 knots (58 mph).
The Walworth County Emergency Manager reported tree damage caused by thunderstorm winds estimated at 50 knots (58 mph).
Law enforcement officials reported tree damage by thunderstorm wind gusts estimated at 56 knots (65 mph).
Fire officials reported tree damage by thunderstorm wind gusts estimated at 56 knots (65 mph).
Based on a report from county emergency managers, an NWS storm survey team determined damage located near the northeast shore of Green Lake was caused by microburst winds estimated at 100 mph (81 knots). Eight homes, a boat and two piers were damaged by the winds. Four dozen trees were uprooted or snapped along the path of the microburst winds.
Fire officials reported tree damage by thunderstorm wind gusts estimated at 56 knots (65 mph).
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2010Every state in 2010This day in weather historyWarnings in Wisconsin, August 2010
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: 258365, 258366, 258367, 258371, 258368, 258369, 258372, 258370, 258533, 258536, 258531, 258539, 258532, 258543, 258537, 258541, 258544, 258549, 258546, 258551, 258547, 258550, 258552, 258557, 258558, 258555, 258553, 258556, 258554.