Multiple rounds of strong to severe thunderstorms moved across southern WI as a warm front slowly moved north through the region. Flash flooding occurred in Washington, Ozaukee, and northern Milwaukee Counties which was followed by prolonged river flooding.
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.
Multiple rounds of strong to severe thunderstorms moved across southern WI as a warm front slowly moved north through the region. Flash flooding occurred in Washington, Ozaukee, and northern Milwaukee Counties which was followed by prolonged river flooding. Four to eight inches of rain had fallen over this area. The thunderstorms produced sporadic tree and power line damage across 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 26, 1:24 PM CST, 1 hour 21 minutes earlier.
Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 224 PM CDT Sun Aug 26 2018 .SHORT TERM... Rest of this Afternoon through Tonight..Forecast Confidence is Medium... Clusters of thunderstorms are expected to move into the western portions of the forecast area around 4 PM or so. These should then move east with time through the evening hours. Additional development can be expected along various outflow boundaries, making for what will likely be a rather messy evening of convection. Instability is quite high across the area, so once convection does develop, there will be an associated wind gust threat. There will also be a threat for large hail, though this will be mitigated somewhat by high freezing levels. The tornado threat is low but non-zero, with eastward surging line segments and boundary interactions as the most likely features from which to see a brief tornado. Additional thunderstorm development is then expected late this evening into the overnight as the low level jet noses into the area. The most widespread activity late tonight should be across central Wisconsin, though a few scattered storms may develop across the southern portion of the state. Along with the threat for severe weather, heavy rain and flooding remain a significant concern. With PWATs in excess of 2 inches, lots of CAPE and high freezing levels, rainfall rates will be very high with any convection this afternoon. Even with progressive movement, today's storms could easily produce a quick 1-2" of rain in less than an hour. The flood and flash flood threat will be greatest across the central and southern forecast area, where soils are most saturated from last week's rainfall. Monday through Tuesday Morning - Confidence...Medium Another hot and humid day is on tap for Monday as southwesterly flow continues across southern Wisconsin. Appears as though there will be some leftover showers extending from central Lake Michigan southwest through southwest Wisconsin Monday morning downstream from an elongated mid level shortwave trough. Once this convection clears by late morning, temperatures should quickly rise while surface dew points linger in the low to mid 70s. Heat indices max out around the mid 90s in the afternoon, so a heat advisory is not looking likely at this point. Convection should then initiate in northwest Wisconsin Monday afternoon and push east-southeast into the low level moisture transport which will be nosing up into northern Wisconsin. The main question is with how far south that MCS makes it and whether it just stays up in northern WI along the strengthening LLJ. Given the strong low level winds, unstable air mass feeding into it (~2000 J/kg 0-3km MUCAPE) and decent 0-6km effective shear of 30-40kts, can not rule out the chance of severe thunderstorms for southern Wisconsin, mainly on Monday night. Damaging winds, large hail and heavy rainfall would be the main concerns. Precipitable water will be up around 2", so some localized flash flooding is certainly possible if the MCS holds up in any areas. .LONG TERM... Tuesday through Wednesday Night - Confidence...Medium Fairly consistent idea between the 26.12z guidance in bringing the cold front into the region on Tuesday but each model has it's own idea of where the convection will initiate. With the ingredients for severe weather will still be there with decent mid level winds and an unstable air mass in place ahead of the front. Just a matter of what the previous night's convection does and where boundaries set up. What happens on Wednesday is a bit up in the air as the previous runs of the NAM/GFS/ECMWF had the front well to the east but now the 26.12z NAM/ECMWF bring another shortwave through the mid level flow and bring another round of convection into the region. Thursday through Saturday - Confidence...Medium to Low With ridging in place for Thursday and Friday, it appears as though there will be a few dry and seasonal days in there before the front lifts back to the north by next weekend. Saturday appears to be the next best chance for storms with the front again cleared by Sunday. && .AVIATION(18Z TAFS)... Thunderstorms are expected to affect the area this evening. There will likely be a prolonged period of scattered activity from late afternoon or early evening into the mid to late evening hours. Did indicate via TEMPO groups the most likely timeframe for thunderstorm impacts, which look to be during the early to mid evening hours. Outside of thunderstorm impacts, winds will start to increase from the southwest later tonight and tomorrow. A few gusts around 20 knots are possible tomorrow mid day through the afternoon. && .MARINE... Areas of Dense Fog will remain possible into early evening, especially north of North Point Light. Fog will be most widespread near open waters. Scattered thunderstorms are likely this evening, and a few could be strong or severe, with gusty winds. Frequent lightning is also expected. Southwest winds will gust to near Small Craft Advisory levels on Monday and Tuesday. There will be additional thunderstorm chances late Monday night and again on Tuesday. A cold front will sweep through the area late Tuesday, with high pressure building into the area on Wednesday and Thursday. && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...Dense Fog Advisory until 7 PM CDT this evening for LMZ643>645. && Tonight/Monday and Aviation/Marine...Boxell Monday Night through Sunday...Halbach
Hazardous Weather Outlook National Weather Service Milwaukee/Sullivan WI 1012 AM CDT Sun Aug 26 2018 WIZ046-047-051-052-056>060-062>072-271515- Marquette-Green Lake-Fond Du Lac-Sheboygan-Sauk-Columbia-Dodge- Washington-Ozaukee-Iowa-Dane-Jefferson-Waukesha-Milwaukee- Lafayette-Green-Rock-Walworth-Racine-Kenosha- 1012 AM CDT Sun Aug 26 2018 This Hazardous Weather Outlook is for portions of east central Wisconsin, south central Wisconsin and southeast Wisconsin. .DAY ONE...This Afternoon and Tonight Heat indices will reach the upper 90s to near 100 today. Thunderstorms are likely later today and tonight, some of which may be severe. Large hail and damaging winds are the main severe threats. In addition, heavy rain will accompany any thunderstorms. This will result in a risk for flooding, especially for areas that have seen very heavy rain over the last week. .DAYS TWO THROUGH SEVEN...Monday through Saturday Additional thunderstorms and an associated risk for heavy rain can be expected again Monday and Tuesday. A few strong or severe thunderstorms are possible during these times as well. The possible heavy rain will result in a risk for flooding, especially for areas that have seen very heavy rain over the last week. Heat index values may reach the middle 90s on Monday. A chance for thunderstorms will return for Friday and Saturday. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed later today into tonight. LMZ643>646-271515- 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- 1012 AM CDT Sun Aug 26 2018 This Hazardous Weather Outlook is for portions of Lake Michigan. .DAY ONE...This Afternoon and Tonight Thunderstorms are likely tonight, some of which may be severe and produce large hail and damaging winds. .DAYS TWO THROUGH SEVEN...Monday through Saturday Thunderstorms are likely at times Monday through Tuesday. There will be a chance that some of the storms may be severe each day through Tuesday. Gusty southwest winds may reach Small Craft Advisory levels Monday and Tuesday. A chance for thunderstorms will return for Friday and Saturday. www.weather.gov/mkx
The La Crosse radar (KARX), 114 km away, was scanning. The volume nearest the first event began at 20:46 UTC.
7 thunderstorm wind, 4 flash flood, 3 flood, 1 lightning, 1 hail. Local standard time, as filed.
At least six different locations of trees or large branches down on roads.
Several trees and power lines down.
A few trees and a powerline down due to a lightning strike.
Estimated wind gusts of 50 mph with 3/4 inch hail in Middleton.
Tree damage concentrated in the Jackson area including one large uprooted tree. A parking sign with a concrete base was tipped over.
Numerous trees and branches down in Jefferson.
Several trees and branches down including two power lines on the west side of Lac La Belle.
A few trees and branches down on Dousman Road.
Numerous trees and branches down on Valley Road.
Flash flooding of some streets in northern Milwaukee County. This included stalled vehicles in flooded intersections of Teutonia Ave. and Capitol Dr. and the intersection of 20th St. and Capitol Dr. Two to four inches of rain had fallen over the area.
Flash flooding of streets in areas of Mequon including the intersection of Cedarburg Rd. and Division St. Additional flash flooding of streets in Grafton and other urban areas of southern Ozaukee County.
Flash flooding of streets in Saukville, Port Washington, Grafton, and other urban and rural areas of southern Ozaukee County.
Flash flooding of city streets in Jackson and West Bend and other urban areas of Washington County. Up to 18 inches of water depth on some streets in West Bend. Flooding of creeks and lowland in rural areas with various roads flooded or washed out. The Town of Farmington experienced the greatest impact from the flooding. Overall, 24 homes had affected flood damage with 5 homes experiencing minor flood damage.
Overall, many flooded roads and lowlands due to 4 to 8 inches of rain. Some road washouts and homes flooded. I-43 was closed through late morning due to flooding between mile marker 101 and 107. Many of the cities in the county experienced severe street flooding and closures. The Milwaukee River reached minor flood stage throughout the county with many roads and intersections flooded and closed near the river, especially near Saukville and Cedarburg. Some piers washed away on the Milwaukee River. Dozens of vehicles across the county were stranded in flood waters. Overall, 76 homes sustained affected flood damage, 52 homes with minor flood damage, and 11 homes with major damage. 25 businesses sustained minor flood damage and 5 businesses sustained major flood damage.
Flooding of lowland and various creeks and rivers continued, including road closures and washouts. The Town of Farmington was impacted the greatest by the flooding.
The Milwaukee River crested at minor flood stage at 12.2 feet during the early afternoon of August 29th, but continued flooding into the evening of September 3rd. Floodwaters spread into the backyards of homes in the Thiensville area. Water is over Elm St., Green Bay Rd., and N. Cedarburg Rd., and into Thiensville Village Park. Water is near some homes along Island Drive and Shoreland Parkway in the Mequon area. There is general lowland flooding in the Cedarburg and Thiensville areas.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wisconsin in 2018Every state in 2018This day in weather historyWarnings in Wisconsin, August 2018
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: 781523, 781525, 781526, 781282, 781527, 781528, 781529, 781530, 781531, 781324, 781336, 781352, 781426, 781396, 781433, 781945.