An upper level short wave trough moved rapidly eastward across the Upper Mississippi River Valley and into Wisconsin during the early morning hours of August 9th. The approaching short wave backed low level winds to the south, which brought a moist, unstable air mass into the region with CAPE values of 2000 to 3000 J/kg.
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.
An upper level short wave trough moved rapidly eastward across the Upper Mississippi River Valley and into Wisconsin during the early morning hours of August 9th. The approaching short wave backed low level winds to the south, which brought a moist, unstable air mass into the region with CAPE values of 2000 to 3000 J/kg. A linear mesoscale convective system developed over Nebraska and moved eastward across northern Iowa on the nose of the 30-35 knot low-level winds. This system moved into Wisconsin shortly after 1 am CDT, with the bowing line of storms producing damaging winds along a 10-mile-wide path as it moved rapidly from west to east across South Central and Southeast Wisconsin. The line of thunderstorms extensively damaged trees and downed power lines, including knocking out electrical power to 1,300 Alliant Energy customers in eastern Sauk County and northwest Dane County. Madison Gas and Electric Company reported about 4,000 of their customers lost power on the southwest side of Madison.
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 8, 2:33 PM CST, 10 hours 12 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 333 PM CDT SUN AUG 8 2010 .SHORT TERM...TONIGHT THROUGH WEDNESDAY. TONIGHT THROUGH MONDAY...FORECAST CONFIDENCE LOW TO MEDIUM. OUTFLOW BOUNDARY AND SUBSIDENCE BEHIND SHORT WAVE THAT DROVE COMPLEX THROUGH CWA THIS MORNING HAVE CLEARED SKIES OVER MOST OF CWA. EXCEPTION IS SLOW EROSION OF STRATUS DECK OVER WRN CWA. CONVECTION DEVELOPING ALONG NEBRASKA/S DAKOTA BORDER IN REGION OF SFC MOISTURE CONVERGENCE AHEAD OF NEXT WAVE ON WATER VAPOR OVER WRN S DAKOTA. IN SPITE OF MODELS TRYING TO GENERATE QPF THIS AFTERNOON DUE TO TOO RAPID A RETURN OF HIGHER DEW POINTS BACK INTO THE REGION...ABOVE MENTIONED SUBSIDENCE AND MIXED LAYER CIN ACROSS ALMOST OF WI AND BACK ACROSS SRN MN AND NRN IOWA WILL PREVENT MUCH GETTING GOING UNTIL WAVE MOVES INTO REGION. WILL TIME CHANCES OF NEXT ROUND OF SHOWERS AND STORMS WITH SHORT WAVE PASSAGE. THIS WILL NOT BRING PCPN INTO THE CWA UNTIL LATE EVENING AT THE EARLIEST...AND MOST LIKELY AFTER 06Z WHEN COMBINATION OF DIFFERENTIAL VORTICITY ADVECTION AND INCREASING LOW-LEVEL JET IN RESPONSE TO APPROACHING WAVE WILL EXPAND CONVECTION INTO EXPECTED MCS. CHANCES FOR SEVERE LOWER WITH CORFIDI VECTORS AND DIFLUENT THICKNESSES INDICATING A SOUTHEASTWARD TURN AS CONVECTION APPROACHES SWRN WI. THIS REFLECTED IN SPC DAY 2 OUTLOOK LIMITED TO THE FAR WRN CWA. WILL KEEP CHANCE POPS ACROSS CWA WITH HIGHER CHANCES IN THE WEST. WITH EXPECTED SWD MOVEMENT OF COMPLEX AND SUBSIDENCE BEHIND WAVE WILL LEAN TOWARD LESS WIDESPREAD PCPN ON LOCAL WRF20 FOR REST OF THE DAY MONDAY. CLOUD DEBRIS AND PCPN WILL FOLLOW CLOSER TO COOLER MET GUIDANCE FOR MONDAY HIGHS. TUESDAY THROUGH WEDNESDAY...FORECAST CONFIDENCE LOW. RESULTANT BOUNDARY LOCATIONS AND TIMING ISSUES WITH SHORT WAVES MAKE IT DIFFICULT TO ATTEMPT TO DRY OUT A GIVEN FORECAST PERIOD. HAVE TRIED TO HIGHLIGHT LIKELY DRY TIMES WITH LOWR POPS/QPF. DEVELOPING EASTERLY FLOW AND PERIODS OF CLOUDS AND PRECIPITATION WILL PREVENT MUCH DAYTIME WARMING AND NIGHTTIME COOLING. CONSENSUS GUIDANCE WAS FOLLOWED. .LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY. FORECAST CONFIDENCE LOW. POSITIONING AND TIMING OF SHORT WAVES STILL PROBLEMATIC IN MAINLY ZONAL FLOW ACROSS NRN U.S. APPEARS WEAK SFC HIGH AND ENOUGH SHORT WAVE RIDGING TO KEEP THURSDAY DRY...AND DELAY NEXT ROUND OF SHOWERS/STORMS UNTIL FRIDAY AFTERNOON/NIGHT WITH WAA AHEAD OF DEEP 500 MB TROUGH. SFC TROUGH AND COLD FRONT ASSOCIATED WITH 500MB TROUGH PASS THROUGH SATURDAY AND EXIT OVERNIGHT TO BRING ANOTHER DRY DAY SUNDAY. HAVE TRIMMED BACK TEMPERATURES A BIT FROM GUIDANCE DUE TO UNCERTAINTY OF PERIODS OF CLOUDS AND SHOWERS VS CLEARING WITH EACH WAVE. && .AVIATION...PLENTY OF SUBSIDENCE IN THE WAKE OF MORNING CONVECTION. SPC MESO PAGE SHOWS BUILDING INSTABILITY ACROSS IA/MN. WILL BANK ON COMPLEX EVOLVING THERE AND SPREADING IN LATER TONIGHT OR SUNDAY MORNING. HAVE MADE SOME MENTION OF THIS POTENTIAL IN THE TAFS. INCLUDED PATCHY MVFR FOG LATER TONIGHT TOO. MET/MAV HITTING IT PRETTY HARD AT KENW AND KMSN...THOUGH CONFIDENCE LOW GIVEN LACK OF IDEAL RADIATIONAL CONDITIONS....BUT TIMING OF ADVANCING CLOUD COVER FROM THUNDERSTORMS MAY END UP BEING KEY AS TO WHETHER CONDITIONS WORSEN BELOW MVFR LEVELS. && .MARINE...WAKE LOW COMBINED WITH DECENT MIXING/STRONG SUBSIDENCE...RESULTING IN A SUSTAINED GUSTY SOUTHWEST WIND REGIME. THIS PROMPTED SMALL CRAFT ISSUANCE. WINDS NOW DROPPING BELOW CRITERIA SO WILL CANCEL HEADLINE. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...NONE. LM...NONE. && SHORT/LONG TERM...09 AVIATION/MARINE...10
HAZARDOUS WEATHER OUTLOOK...UPDATED NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 134 AM CDT SUN AUG 8 2010 WIZ046-047-051-052-056>060-062>072-090900- MARQUETTE-GREEN LAKE-FOND DU LAC-SHEBOYGAN-SAUK-COLUMBIA-DODGE- WASHINGTON-OZAUKEE-IOWA-DANE-JEFFERSON-WAUKESHA-MILWAUKEE- LAFAYETTE-GREEN-ROCK-WALWORTH-RACINE-KENOSHA- 134 AM CDT SUN AUG 8 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EAST CENTRAL WISCONSIN...SOUTH CENTRAL WISCONSIN AND SOUTHEAST WISCONSIN. .DAY ONE...TONIGHT THUNDERSTORMS ARE EXPECTED ACROSS MUCH OF SOUTHERN WISCONSIN. SOME OF THE STORMS COULD BE SEVERE...WITH DAMAGING WIND GUSTS THE PRIMARY THREAT. THE BEST CHANCE FOR SEVERE STORMS IS FROM ABOUT JANESVILLE WEST AND THE WISCONSIN DELLS SOUTH. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY A FRONTAL BOUNDARY WILL REMAIN ANCHORED ACROSS THE WESTERN GREAT LAKES AS SEVERAL WEAK LOW PRESSURE SYSTEMS PASS THROUGH THE REGION THROUGH EARLY THIS WEEK. THESE CONDITIONS WILL SUSTAIN A PERSISTENT CHANCE OF THUNDERSTORMS FROM MONDAY INTO WEDNESDAY. ALSO...A PROLONGED PERIOD OF VERY WARM AND HUMID CONDITIONS IS EXPECTED FROM MONDAY THROUGH THURSDAY. AFTERNOON HEAT INDEX VALUES WILL REACH THE 90S EACH DAY. THERE IS A CHANCE FOR MORE THUNDERSTORMS NEXT FRIDAY AND SATURDAY AS A STRONGER COLD FRONT IS EXPECTED TO SWEEP ACROSS THE WESTERN GREAT LAKES REGION. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL MOST LIKELY NOT BE BE NEEDED. LMZ643>646-090900- 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- 134 AM CDT SUN AUG 8 2010 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF LAKE MICHIGAN. .DAY ONE...REST OF TODAY AND TONIGHT THUNDERSTORMS ARE EXPECTED LATER TONIGHT. SOME OF THE STORMS MAY BE STRONG WITH GUSTY WINDS...BUT OVERALL THE STORMS ARE EXPECTED TO REMAIN BELOW SEVERE LEVELS. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY A FRONTAL BOUNDARY WILL LINGER ACROSS THE AREA FROM MONDAY AND TUESDAY BEFORE A WEAK COOL FRONT PASSES ACROSS LAKE MICHIGAN ON WEDNESDAY. THESE WEATHER SYSTEMS WILL RESULT IN A PERSISTENT CHANCE OF THUNDERSTORMS FROM MONDAY THROUGH WEDNESDAY. THERE IS A CHANCE FOR MORE THUNDERSTORMS NEXT FRIDAY AND SATURDAY AS A STRONGER COLD FRONT IS EXPECTED TO SWEEP ACROSS THE WESTERN GREAT LAKES REGION. COLLAR/DDV WWW.WEATHER.GOV/MKX
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI 1230 AM CDT MON AUG 9 2010 WIZ056-062-063-067-068-090700- DANE-GREEN-IOWA-LAFAYETTE-SAUK- 1230 AM CDT MON AUG 9 2010 ...STRONG LINE OF THUNDERSTORMS MOVING INTO SOUTHWEST AND SOUTH CENTRAL WISCONSIN... AT 1226 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 84 MILES WEST OF REEDSBURG TO 62 MILES WEST OF DODGEVILLE TO 60 MILES WEST OF DARLINGTON...MOVING EAST AT 50 MPH. ONE HALF INCH DIAMETER HAIL...WINDS GREATER THAN 40 MPH...CONTINUOUS CLOUD TO GROUND LIGHTNING...HEAVY DOWNPOURS...ARE POSSIBLE WITH THESE STORMS. * THUNDERSTORMS WILL BE NEAR... BLACKHAWK LAKE RECREATION AREA AND BENTON BY 120 AM CDT... SHULLSBURG BY 125 AM CDT... MINERAL POINT AIRPORT AND LONE ROCK AIRPORT BY 130 AM CDT... GOVERNOR DODGE STATE PARK AND DODGEVILLE BY 135 AM CDT... SPRING GREEN BY 140 AM CDT... YELLOWSTONE LAKE STATE PARK BY 145 AM CDT... BLUE MOUND STATE PARK AND BLANCHARDVILLE BY 150 AM CDT... GUSTY WINDS MAY CAUSE SMALL OBJECTS SUCH AS TRASH BINS TO BLOW AROUND. STAY AWAY FROM HIGH OBJECTS OUTDOORS SUCH AS TREES. SEEK SHELTER IN A STURDY STRUCTURE UNTIL THESE STORMS HAVE PASSED. GEHRING
The La Crosse radar (KARX), 124 km away, was scanning. The volume nearest the first event began at 06:44 UTC.
13 thunderstorm wind. Local standard time, as filed.
Sheriff deputies reported large trees were blown down by thunderstorm wind gusts estimated up to 56 knots (65 mph).
Sheriff deputies reported extensive trees damage from thunderstorm wind gusts estimated at 65 knots (75 mph).
Sheriff deputies reported large trees down over many locations across eastern Iowa County from damaging thunderstorm wind gusts.
Sheriff deputies reported sporadic damage to large trees from damaging thunderstorm wind gusts estimated at 65 knots (75 mph).
Sheriff deputies reported large trees and power lines blown down from damaging thunderstorm wind gusts estimated at 65 knots (75 mph).
Sheriff deputies reported damage to large trees from thunderstorm wind gusts estimated at 56 knots (64 mph).
Sheriff deputies reported large trees blown down from damaging thunderstorm wind gusts estimated at 65 knots (75 mph). A large tree fell on a house in the 7000 block of Sagebrush Trail, resulting in minor damage.
Sheriff deputies reported sporadic tree damage from thunderstorm wind gusts estimated at 56 knots (65 mph).
Police officials reported tree damage and building damage from thunderstorm wind gusts estimated at 65 knots (75 mph).
Police officials reported considerable tree damage from thunderstorm wind gusts estimated at 65 knots (75 mph).
Police officials reported trees and power lines blown down from damaging thunderstorm wind gusts estimated at 56 knots (65 mph).
Police officials reported considerable tree damage from thunderstorm wind gusts estimated at 56 knots (65 mph). The AWOS at West Bend airport recorded a 60 mph (52 knot) wind gust at 350 am CDT.
Police officials reported trees blown down from damaging thunderstorm wind gusts. A mesonet site on the campus of Divine Savior-Holy Angels High School measured a thunderstorm wind gust of 62 mph (54 knots) at 4 am CDT.
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: 255637, 255641, 255638, 255642, 255639, 255643, 255640, 255644, 255645, 255646, 255648, 255647, 255649.