A line of severe thunderstorms ahead of an approaching cold front brought two tornadoes, flash flooding, and straight-line wind damage to far southern WI.
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 line of severe thunderstorms ahead of an approaching cold front brought two tornadoes, flash flooding, and straight-line wind damage to far southern WI.
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 10, 11:09 AM CST, 1 hour earlier.
Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 1209 PM CDT Mon Aug 10 2020 .MESOSCALE DISCUSSION... (Issued 1209 CDT Mon Aug 10 2020) Updated for SPC Moderate Risk. Risk for high end wind gusts, particularly for Lafayette, Green, Rock, Walworth, Racine and Kenosha Counties. Active afternoon of weather coming up for the region. Currently monitoring a nasty line of storms plowing through Central IA. Numerous measured reports of winds in excess of 60mph, with Des Moines recently posting a 75mph gust. The environment out ahead of this line only gets better instability-wise. As a result, SPC has included counties adjacent to the IL state line in a MDT risk and areas along/south of I-94 in a PDS Severe Thunderstorm watch due to the potential for high end wind gusts. As with anything, there are some questions as to how things will unfold north of the I-94 corridor. Currently, the most vigorous line of storms is just east of Des Moines and moving eastward. Additional deep convection is percolating across northeastern IA. Instability is no issue with lifted indices pushing -10. Mixed layer CAPE is already well in excess of 2000 J/kg and poised to increase to around 3000 J/kg in the next few hours. In addition, it appears we will see an uptick in low level CAPE. As we continue to see convection mature and congeal on the northern portion of this line, this will be a helpful ingredient for organization. Finally, low level theta-e differences are in excess of 25 K and DCAPE values in excess of 1000 J/kg support the risk of severe wind gusts. Shear is still somewhat marginal, but largely a moot point as the atmosphere has shown its cards. 0-3km shear is lacking as well, though it is oriented from west to east and with increasing low level CAPE, it does warrant watching for potential mesovortex development and the potential for a few spin up tornadoes. Overall, a more outflow dominate line is the preferred mode, but anywhere this line remains balanced will be an area to watch for mesovortex development. Bottom line - the wind threat is greatest with the incoming line, highlighted by areas in the moderate risk (Lafayette, Green, Rock, Walworth, Racine and Kenosha Counties). The risk toward counties in the I-94 corridor is more conditional on storm organization and cold pool conglomeration into a linear mode in the next few hours. The PDS Severe Thunderstorm Watch handles the areas at greatest risk well. Areas further north can still expect thunderstorm development and a few strong/severe storms with wind gusts the primary concern. GAGAN && .SHORT TERM... (Issued 340 AM CDT Mon Aug 10 2020) Today and Tonight: There is a shallow low level inversion this morning, which could cause some patchy fog to develop in low lying areas and river valleys. Any fog that develops this morning should begin to dissipate shortly after sunrise. Scattered thunderstorms are expected to develop and move across southern Wisconsin from late this morning into the evening hours. These thunderstorms will be associated with the passage of the cold front. A few strong/severe storms will be possible, with instability pushing 3000+ J/kg and deep layer bulk shear around 20 to 25 knots. There remains some uncertainty with the timing and areal coverage of these thunderstorms, due to the only forcing being associated with the cold front. Quiet conditions are expected to return by later tonight, as drier air and high pressure moves into the region. The high pressure will bring clearing skies and light winds. With calm conditions expected overnight, it's not out of the question for some fog to develop. Patterson && .LONG TERM... (Issued 340 AM CDT Mon Aug 10 2020) Tuesday through Wednesday: Models are in pretty good agreement with high pressure lingering over the region Tuesday into Tuesday night, then slowly moving to the east on Wednesday. This should bring a period of dry conditions and warm temperatures to the area. Lake breezes should occur by each afternoon near Lake Michigan. Wednesday Night through Thursday Night: Models are generally showing a broad 500 mb trough developing over the middle Mississippi River Valley northward into Wisconsin Wednesday night into Thursday night. The main southerly low level jet feed of moisture should remain west of the area during this period. Forecast soundings do suggest some instability develops by Thursday. The upward vertical motion fields are rather weak during this time, so uncertainty remains with if any showers and storms develop. Ensembles also show very low QPF occurring during these periods. For now, left small PoPs going for this period, though it may trend drier if the main low level jet feed remains to the west, and upward vertical motion fields remain weak. Warm and somewhat more humid conditions are expected during this period. Friday Through Sunday: Fairly large amount of uncertainty exists during this period across the area, as differences abound between the GFS and ECMWF. The GFS pushes the weak 500 mb trough east of the area Friday night, with generally zonal flow occurring over the weekend. It does have a vorticity maximum moving east through the region by Sunday. The ECMWF has a cutoff 500 mb low that sits over Iowa and Illinois Friday into Saturday, before shifting east Saturday night and Sunday. It then brings another shortwave trough southeast into the region for Sunday. Thus, the ECMWF is wetter during this period, though both have QPF in the area Sunday. The ensembles are generally showing very low QPF and PoPs for most of this period, reflecting the uncertainty. For now, kept blended model PoPs with rather low confidence on what will occur during this period. Temperatures remain warm with humid conditions lingering. JJW && .AVIATION... (Issued 1021 AM CDT Mon Aug 10 2020) For the 18Z TAFs: IFR to MVFR ceilings will linger over the next few hours. Ceilings should improve as we head into the afternoon, but scattered thunderstorms are expected to develop and move across southern Wisconsin with the cold front. There is a concern for storms to be severe with gust up to 60 knots and maybe some quarter sized hail. Expect flight conditions to deteriorate to MVFR/IFR values within any thunderstorm. Once the cold front passes northwest winds and VFR conditions move in. RAH && .MARINE... (Issued 340 AM CDT Mon Aug 10 2020) Scattered thunderstorms are expected to move across the lake from around midday into this evening, with the passage of a cold front. A few strong/severe storms are possible during this period. Southerly winds are expected to persist through the morning hours, before shifting to northwesterly by this evening. Quiet conditions are expected to return by later tonight, as high pressure builds into the area. Patterson && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. &&
Hazardous Weather Outlook...UPDATED National Weather Service Milwaukee/Sullivan WI 1135 AM CDT Mon Aug 10 2020 WIZ046-047-051-052-056>060-062>072-111645- Marquette-Green Lake-Fond du Lac-Sheboygan-Sauk-Columbia-Dodge- Washington-Ozaukee-Iowa-Dane-Jefferson-Waukesha-Milwaukee- Lafayette-Green-Rock-Walworth-Racine-Kenosha- 1135 AM CDT Mon Aug 10 2020 This Hazardous Weather Outlook is for portions of east central Wisconsin, south central Wisconsin and southeast Wisconsin. .DAY ONE...This Afternoon and Tonight Thunderstorms are expected to roll across southern Wisconsin today. A Severe Thunderstorm Watch is in effect for counties generally along and south of I-94. Hail up to one inch and wind gusts to 60 MPH with gusts up to 80 MPH are possible. Heat index values may reach the middle 90s today in southeastern parts of the area. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday There are small chances for thunderstorms Thursday through Friday, with chances for storms lingering Saturday into Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation is needed today into this evening. LMZ643>646-111645- 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- 1135 AM CDT Mon Aug 10 2020 This Hazardous Weather Outlook is for the nearshore waters from Sheboygan Wisconsin to Winthrop Harbor Illinois. .DAY ONE...This Afternoon and Tonight Thunderstorms are forecast to develop and move east across the nearshore waters this afternoon through early this evening as a cold front moves southeast through the region. A Severe Thunderstorm Watch is in effect. Severe storms with hail to one inch and wind gusts to 60 knots possible. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday There are small chances for thunderstorms Thursday through Friday, with chances for storms lingering Saturday into Sunday. LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868- 870-872-874-876-878-111645- Lake Michigan Michigan City IN to St. Joseph MI 5 NM offshore to mid-line of lake.- Lake Michigan from Seul Choix Point to Rock Island Passage 5NM offshore to Mid Lake- Lake Michigan South of a line from Seul Choix Point to the Mackinac Bridge and North of a line from Charlevoix MI to South Fox Island 5NM offshore- Lake Michigan from Charlevoix to Point Betsie MI 5NM Offshore to mid lake- Lake Michigan from Point Betsie to Manistee MI 5NM offshore to Mid Lake- Lake Michigan from Rock Island Passage to Sturgeon Bay WI 5NM offshore to mid lake- Lake Michigan from Sturgeon Bay to Two Rivers WI 5NM offshore to Mid Lake- Lake Michigan from Two Rivers to Sheboygan WI 5NM offshore to Mid Lake- Lake Michigan from Sheboygan to Port Washington WI 5NM offshore to Mid Lake- Lake Michigan from Port Washington to North Point Light WI 5NM offshore to Mid Lake- Lake Michigan from North Point Light to Wind Point WI 5NM offshore to Mid Lake- Lake Michigan from Wind Point WI to Winthrop Harbor IL 5NM offshore to Mid Lake- Lake Michigan from Winthrop Harbor to Wilmette Harbor IL 5NM offshore to Mid Lake- Lake Michigan from Wilmette Harbor to Michigan City in 5NM offshore to Mid Lake- Lake Michigan from Pentwater to Manistee MI 5NM offshore to Mid Lake- Lake Michigan from Whitehall to Pentwater MI 5NM offshore to Mid Lake- Lake Michigan from Grand Haven to Whitehall MI 5NM offshore to Mid Lake- Lake Michigan from Holland to Grand Haven MI 5NM offshore to Mid Lake- Lake Michigan from South Haven to Holland MI 5NM offshore to Mid lake- Lake Michigan from St Joseph to South Haven MI 5NM offshore to Mid Lake- 1135 AM CDT Mon Aug 10 2020 This Hazardous Weather Outlook is for the open waters of Lake Michigan. .DAY ONE...This Afternoon and Tonight Thunderstorms are forecast to develop and move east across the nearshore waters this afternoon through early this evening as a cold front moves southeast through the region. A Severe Thunderstorm Watch is in effect. Severe storms with hail to one inch and wind gusts to 60 knots possible. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday There are mainly small chances for thunderstorms Friday, with chances for storms lingering Saturday into Sunday. MRC www.weather.gov/mkx
The Quad Cities radar (KDVN), 127 km away, was scanning. The volume nearest the first event began at 18:10 UTC.
14 thunderstorm wind, 2 tornado, 2 flash flood, 1 heavy rain. Local standard time, as filed.
A semi-truck tipped over on highway 151 due to straight-line winds.
Tree limbs and power lines down on the south side of Darlington. Also a blown transformer.
Many large tree limbs down in yard, some on the house. Three trees down on a nearby road.
A downed tree in Monroe.
Measured wind gust of 62 mph at Monroe airport.
A tree down on a road.
Weak tornado started on the southeast end of Geneva Lake and went through the southeast side of Lake Geneva. Mainly tree damage along the path, but some minor structural damage in the business district bounded by highways 120, 50 and 12. Path appeared to end just south of the Grand Geneva resort.
Tornado started in NW Lake County Illinois where some house and structural damage occurred just south of the WI/IL border. The tornado then crossed into Wisconsin and knocked hundreds of trees down (trunks snapped and uprooted) at Promised Land camp. Tornado continued northeast toward the southwest side of Camp Lake where shingle damage was noted on a few houses. Tornado then crossed Camp Lake and exited it on the northeast side where more tree damage was noted. Some pontoon boats and docks were toppled on Camp Lake. Tornado was embedded within a line of storms that also had winds of 50-60 mph.
Large tree limbs and power lines down.
An estimated wind gust of 60 mph.
Several trees down around the intersection of 93rd St. and 388th Ave.
Flash flooding of streets in the Elkhorn area including on 1st Ave and on W. Hidden Trail just west of highway 67.
Scattered large tree branches down in Kenosha.
Scattered tree limbs or trees down in Union Grove.
Scattered tree limbs and trees down throughout Elmwood Park. Some damage to the siding of a home.
Scattered tree limbs and trees down throughout Racine. A large Willow tree was uprooted on the south side of Racine.
Scattered large branches down in North Bay.
Flash flooding of streets and creeks across much of Racine County after a quick 2 to 4 inches of rain. This included Waterford, Burlington, Franksville, and Racine. Some road closures were needed. Four cars stalled in 2 to 3 feet of standing water on Douglas Ave. near Middle Rd. northwest of Wind Point. Flash flooding led to a sink hole at the entrance road to Quarry Lake Park.
Some minor street flooding in far southern Milwaukee County. Water across the intersection of Elm Rd. and Nicholson Rd.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2020Every state in 2020This day in weather historyThe tornado archive for Wisconsin, 2020Warnings in Wisconsin, August 2020
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: 901584, 901585, 901586, 901589, 901588, 901587, 909501, 909502, 901591, 901592, 901590, 906858, 901602, 901603, 901600, 901601, 901604, 906468, 906743.