A surge of warm, moist, and unstable air aloft brought large thunderstorm complexes across southern WI during the evening of July 19th into the early morning hours of July 20th. The first thunderstorm complex brought damaging straight line winds to portions of south central WI, and was immediately followed by a wake low which also produced strong, damaging winds.
Every event with a place to put it; 3 filed by county or forecast zone are drawn at its center, in a lighter ring. 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 surge of warm, moist, and unstable air aloft brought large thunderstorm complexes across southern WI during the evening of July 19th into the early morning hours of July 20th. The first thunderstorm complex brought damaging straight line winds to portions of south central WI, and was immediately followed by a wake low which also produced strong, damaging winds. Repeated rounds of heavy rain of 3-5 inches also produced flooding mostly south and west 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 Jul 19, 2:14 PM CST, 3 hours 41 minutes earlier.
Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 314 PM CDT Wed Jul 19 2017 .SHORT TERM...Tonight through Thursday MCS roaring through MN this afternoon with a path taking it towards southern WI riding along a boundary that stretches just south of the area or at least running through southwest or southern WI. Huge dewpoint gradient exists at this time with upper 50s in Sheboygan to lower and mid 70s just south and west of Madison. MCS will pack a punch most likely with damaging winds and heavy rainfall possible...to pin point an exact track is still iffy but it looks like the area will be impacted by this convective system. Another less likely issue will be behind the system...possible that strong low level jet perpendicular to the boundary may help to produce some training cells that could drop heavy rainfall of a narrow area. Much to watch tonight! Thursday should see a period of dry conditions with some clouds lingering...small chance that a few afternoon/evening showers or thunderstorms could develop. Warm and humid conditions continue. .LONG TERM...Friday through Tuesday Friday begins a second punch of possible heavy rainfall with showers and thunderstorms possible through the day. the set-up is ripe for heavy rainfall with solid dynamics and High PWATS. would be possible for some to see 2 to 3 inches of rain on Friday. Slight risk for severe storms on that day...but with many areas very wet at this time flooding concerns are the main threat especially for those hit so hard last week. Temps hanging in the lower 80s for highs. Over the weekend the chances for showers and thunderstorms are lesser on Sunday than Saturday. Warmer temps on Sat with mid 80s and just a bot cooler on Sunday with temps barely hitting 80. After the weekend mainly dry and pleasant late July conditions look to continue to start next week with highs in the mid to upper 70s and dewpoints in the 50s. && .AVIATION(18Z TAFS)... Multiple concerns for the TAF period...stratocu lifting across much of Southern WI is the first concern...no so much at MKE or UES...but elsewhere an issue for a few more hours at least. The second concern is the huge thunderstorm complex nearing the MN/IA border from SD...it should continue to move south and east towards the region overnight into the area. Timing will be an issue and it may be earlier than forecast...but it should be expected and will have the possible impact of strong gusty winds at times and low visibility and ceilings when it impacts the region. Finally the last concern will be wind shear overnight...significant low level jet will be present and linger through the early morning hours of Thursday. Outside of this light to modest winds and mainly VFR conditions. && .MARINE... Clouds have lifted from this morning with mainly clear skies...light winds from the northeast or east will continue. waves should be very modest at best with the only real concern the possible shot of thunderstorms from the system moving across MN at this time. After that threat passes by early morning...light winds and modest wave action will continue through the day Thursday. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. && Tonight/Thursday and Aviation/Marine...ABS Thursday Night through Wednesday...ABS
Hazardous Weather Outlook National Weather Service Milwaukee/Sullivan WI 331 PM CDT Wed Jul 19 2017 WIZ046-047-051-052-056>060-062>072-202045- Marquette-Green Lake-Fond Du Lac-Sheboygan-Sauk-Columbia-Dodge- Washington-Ozaukee-Iowa-Dane-Jefferson-Waukesha-Milwaukee- Lafayette-Green-Rock-Walworth-Racine-Kenosha- 331 PM CDT Wed Jul 19 2017 This Hazardous Weather Outlook is for portions of east central Wisconsin, south central Wisconsin, and southeast Wisconsin. .DAY ONE...Tonight A line of thunderstorms is expected to cross primarily south central and southwest Wisconsin during the late evening. The greatest threat from these storms is damaging wind up to 70 mph. Secondary threats would include large hail, heavy rain, and possibly a tornado. Additional thunderstorms are possible late tonight across all of southern Wisconsin. These storms may also be severe with damaging winds, large hail, and heavy rain possible. .DAYS TWO THROUGH SEVEN...Thursday through Wednesday There is a slight chance of thunderstorms on Thursday and Thursday night. Thunderstorms are likely Friday afternoon through Saturday morning. Repeated rounds of storms over the same area may produce heavy rain that would affect the already high rivers. Gusty winds and hail are possible at times as well. There is a slight risk for severe storms during this period. Heat index values in the middle 90s are forecast across mainly southern and western portions of the area Thursday into Saturday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed Tonight. LMZ643>646-202045- 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- 331 PM CDT Wed Jul 19 2017 This Hazardous Weather Outlook is for portions of Lake Michigan. .DAY ONE...Tonight Thunderstorms are possible late tonight. These storms may be severe with damaging winds and large hail possible. .DAYS TWO THROUGH SEVEN...Thursday through Wednesday There is a slight chance of thunderstorms on Thursday and Thursday night. Thunderstorms are likely Friday through Saturday morning. Gusty winds and hail are possible at times. There is a slight risk for severe storms during this period. SPM www.weather.gov/mkx
The La Crosse radar (KARX), 114 km away, was scanning. The volume nearest the first event began at 23:55 UTC.
9 thunderstorm wind, 2 high wind, 2 heavy rain, 1 strong wind. Local standard time, as filed.
Large branches and power lines down in the western portion of the county including Cobb and Mineral Point.
Trees and power lines down in the western portion of the county.
Trees and power lines down and damage to a metal shed.
Trees and power lines down in multiple areas of the county including the city of Monroe.
Trees and power lines down.
Trees and power lines down in the far western portions of the county.
Large tree branches down.
Greater than 2 inch diameter tree branches down.
Several trees and branches down throughout the county.
Wake low wind gusts downing tree branches.
Wake low wind damage especially in the communities of Mount Horeb, Verona, Mt. Vernon, and the southwest side of Madison. Significant tree damage occurred. There was minor structural damage to homes in Mount Horeb due to trees landing on them or shingles being removed from high winds.
Wake low wind damage to trees and branches across the county.
The west branch of the Little Sugar River and the Little Sugar River flooded during the afternoon of July 20th after several inches of overnight rain. A small number of roads near the river were closed and the parking lot for the Badger and Sugar River Bike Trails was flooded. In downtown Monticello, basement flooding occurred at a cafe, the village hall, and a chemical LLC. A portion of Fahey Road, south of Belleville, was washed out during the morning hours.
Washouts of mainly gravel roads and driveways in the northwest portion of the county. About 50 homes with mostly minor water damage. However, the north foundation of a home collapsed while the east and west foundations buckled due to water pressure. Water was briefly over a bridge on Sunny Road at the Dodge Branch of the Pecatonica River. The flooding also led to the loss of crops.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2017Every state in 2017This day in weather historyWarnings in Wisconsin, July 2017
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: 712940, 712941, 712942, 712944, 712943, 712945, 712946, 712948, 712947, 712955, 712953, 712954, 716265, 716262.