A cold front brought intensifying thunderstorms across east-central Wisconsin during the afternoon as it swept through the region. Three tornadoes and wind damage was reported as these thunderstorms tracked through the area.
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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 GRB wrote it up.
A cold front brought intensifying thunderstorms across east-central Wisconsin during the afternoon as it swept through the region. Three tornadoes and wind damage was reported as these thunderstorms tracked through the area.
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 Green Bay, WI wrote its last area forecast discussion before the first event at Jun 20, 2:02 PM CST, 1 hour 35 minutes earlier.
Area Forecast Discussion National Weather Service Green Bay WI 302 PM CDT Sat Jun 20 2020 Forecast discussion for routine afternoon forecast issuance .SHORT TERM...Tonight and Sunday Issued at 301 PM CDT Sat Jun 20 2020 Shortwave lifting northeast across Wisconsin will continue to produce showers and thunderstorms through the mid evening hours. Considerable cloud cover and precipitation have kept temperatures and instability in check. There is a small chance of a strong or marginally severe storm south of highway 10 during the late afternoon or early evening hours in the vicinity of the warm front. Locally heavy rain is possible through early evening hours, which could produce local flooding in some places. Lows tonight will be a few degrees above normal. Sunday should be pretty nice for Father's Day activities. It will be a little less humid than the last few days, with temperatures a few degrees above normal. There could be scattered showers late in the day in the western part of the forecast area as the next system approaches. .LONG TERM...Sunday Night Through Saturday Issued at 301 PM CDT Sat Jun 20 2020 Focus on the long term remains storm chances and flooding threat Sunday night into Monday night, with additional shower/storm chances Tuesday-Thursday and again late in the week. Temps look to generally be between 10 degrees below normal and 5 degrees above normal. Sunday night into Monday night...the 500mb low will slowly shift into western Ontario, as a piece of shortwave energy rotates into Wisconsin and a weak surface low and cold front push across the area. Showers/storms look to be ongoing Sunday afternoon/evening west of the area, then spread into our area as these features push east. Still some uncertainty on how exactly things will play out, as models differ slightly on timing/location of features and clusters of storms, but expect at least a round or two of storms across the area starting late Sunday evening and another round on Monday as the front drops across the area. Severe weather threat remains low do to limited instability; however, a severe storm or two can't be ruled out across central and east central WI ahead of the front. Bigger issue could be flooding as PWATs climb over 1.5" and any slow moving or training storms will create flooding issues, especially where the heaviest rain fell today. The threat for river flooding will also be increasing into early next week as a lot of water has fallen in some river basins. A few lingering showers are possible behind the front Monday night, but this activity will be on the lighter side. Tuesday into Thursday...northwest/cyclonic flow takes over across the region as the 500mb low remains slowly drifts east across Ontario. Expect a dry start each day then chances for showers and isolated storms increase in the late morning and afternoon as diurnally driven activity is expected, ending in the evening hours. Strongest activity could produce some hail as wet bulb temps will be under 8500 ft. Model soundings also showing a weak inverted V signature. Although there is no strong winds to mix down, evaporative cooling effects could produce some gusty winds in any storm. By Thursday...heights continue to build as ridging builds in from the west, reducing the chance for instability showers, but a few still can't be ruled out. Rest of the forecast...500mb low drifts into eastern Ontario and eventually Quebec late in the week, with the flow becoming more zonal across the CONUS. Another upper trough and surface low pressure is forecast to push across the area somewhere in the Friday or Saturday timeframe, bringing shower and storms back to the area. && .AVIATION...for 18Z TAF Issuance Issued at 1234 PM CDT Sat Jun 20 2020 Variable conditions are expected today with a lot of showers and thunderstorms ahead of a slow moving front. Conditions should be MVFR most of the time in most places, but brief heavy rain and IFR conditions are possible. The activity should end early this evening, but leftover moisture will result in low clouds and fog formation overnight. Improving conditions are expected Sunday morning, with VFR conditions by Sunday afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && SHORT TERM.....RDM LONG TERM......Bersch AVIATION.......RDM
Hazardous Weather Outlook National Weather Service Green Bay WI 253 PM CDT Sat Jun 20 2020 WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-212000- Vilas-Oneida-Forest-Florence-Northern Marinette County-Lincoln- Langlade-Menominee-Northern Oconto County-Door-Marathon-Shawano- Wood-Portage-Waupaca-Outagamie-Brown-Kewaunee-Waushara-Winnebago- Calumet-Manitowoc-Southern Marinette County- Southern Oconto County- 253 PM CDT Sat Jun 20 2020 This Hazardous Weather Outlook is for north-central and northeast Wisconsin. .DAY ONE...Tonight Scattered thunderstorms are expected into the early evening hours. There is a small chance that a storm could become marginally severe south of Highway 29 with strong winds and hail. Localized very heavy rain could produce urban and small stream flooding in some places. .DAYS TWO THROUGH SEVEN...Sunday through Saturday Additional rounds of showers and thunderstorms are possible at times from Sunday night through Monday night. A few of the storms could become strong or severe with large hail and damaging winds Monday into Monday evening across central and portions of east- central Wisconsin. Heavy rainfall and localized flooding will also be possible late Sunday into Monday evening. Isolated storms are possible Tuesday and Wednesday afternoon, with the strongest activity producing hail and brief gusty winds. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected, but spotters are asked to report any flooding or strong winds. LMZ521-522-541>543-212000- The Bay of Green Bay south of a line from Cedar River MI to Rock Island Passage-Lake Michigan from Washington Island to Sheboygan- 253 PM CDT Sat Jun 20 2020 This Hazardous Weather Outlook is for portions of northwest Lake Michigan and the waters of Green Bay. .DAY ONE...Tonight Scattered thunderstorms are expected this evening. A few of the storms south of Algoma could produce wind gusts over 40 knots. Areas of fog could pose a hazard to boaters tonight. .DAYS TWO THROUGH SEVEN...Sunday through Saturday Scattered thunderstorms will pose a hazard to boaters at times Sunday night through Wednesday. Some of the storms could produce hail and strong winds Monday into Monday evening. RDM/Bersch
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREEN BAY WI
1221 PM CDT SAT JUN 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1215 PM HEAVY RAIN KNOWLTON 44.71N 89.68W
06/20/2020 M3.00 INCH MARATHON WI PUBLIC
&&
AKSpecial Weather Statement
National Weather Service Green Bay WI
212 PM CDT Sat Jun 20 2020
WIZ040-050-201945-
Kewaunee WI-Manitowoc WI-
212 PM CDT Sat Jun 20 2020
...LOCALLY STRONG THUNDERSTORMS MOVING ACROSS EAST-CENTRAL
WISCONSIN...
At 209 PM CDT, Doppler radar was tracking a cluster of strong
thunderstorms along a line extending from 6 miles east of Denmark to
10 miles east of Cleveland. Movement was northeast at 40 mph.
Winds in excess of 30 mph will be possible with these storms.
Locations impacted include...
Kewaunee, Algoma, Luxemburg, Two Creeks, Two Rivers, Mishicot, Casco,
Birchwood, Pilsen and Krok.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4455 8776 4468 8743 4467 8738 4471 8734
4467 8733 4454 8741 4432 8748 4418 8745
4407 8760
TIME...MOT...LOC 1909Z 223DEG 35KT 4437 8770 4390 8754
KallasPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREEN BAY WI
239 PM CDT SAT JUN 20 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0237 PM HEAVY RAIN PLOVER 44.45N 89.53W
06/20/2020 M1.46 INCH PORTAGE WI CO-OP OBSERVER
&&
TIMMUSpecial Weather Statement National Weather Service Green Bay WI 329 PM CDT Sat Jun 20 2020 WIZ031-036>038-045-048-202115- Waupaca WI-Shawano WI-Outagamie WI-Winnebago WI-Waushara WI- Portage WI- 329 PM CDT Sat Jun 20 2020 ...SPECIAL WEATHER STATEMENT... At 328 PM CDT, Doppler radar was tracking thunderstorms along a line extending from 5 miles south of Lake Poygan to near Hartman Creek State Park. Movement was northeast at 35 mph. Winds in excess of 30 mph will be possible with these storms. Locations impacted include... Waupaca, New London, Clintonville, Black Creek, Amherst, Fremont, Napowan Scout Camp, Lake Poygan, Hartman Creek State Park and Chain O' Lakes-King. PRECAUTIONARY/PREPAREDNESS ACTIONS... If outdoors, consider seeking shelter inside a building. Torrential rainfall is also occurring with these storms, and may lead to localized flooding. Do not drive your vehicle through flooded roadways. && LAT...LON 4442 8836 4482 8910 4427 8941 4396 8884 TIME...MOT...LOC 2028Z 209DEG 30KT 4407 8888 4429 8929 RDM
Special Weather Statement
National Weather Service Green Bay WI
415 PM CDT Sat Jun 20 2020
WIZ031-037>039-048-202200-
Waupaca WI-Shawano WI-Outagamie WI-Winnebago WI-Brown WI-
415 PM CDT Sat Jun 20 2020
...SPECIAL WEATHER STATEMENT...
At 412 PM CDT, Doppler radar was tracking thunderstorms south of a
line from near Amherst to Bear Creek to 5 miles west of Menasha.
Movement was northeast at 30 mph.
Winds in excess of 30 mph will be possible with these storms.
Locations impacted include...
Appleton, Shawano, Menasha, Kaukauna, Little Chute, New London,
Kimberly, Clintonville, Black Creek and Embarrass.
The thunderstorms could intensify in the next hour or two as they
move to the northeast.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 4443 8886 4444 8922 4450 8922 4482 8883
4481 8843 4443 8807 4424 8835 4424 8840
4421 8840 4411 8855
TIME...MOT...LOC 2112Z 218DEG 23KT 4436 8936 4449 8920 4449 8880 4422
8855
RDMSpecial Weather Statement
National Weather Service Green Bay WI
429 PM CDT Sat Jun 20 2020
WIZ038-048-202215-
Outagamie WI-Winnebago WI-
429 PM CDT Sat Jun 20 2020
...SIGNIFICANT WEATHER ADVISORY FOR WINNEBAGO AND SOUTHWESTERN
OUTAGAMIE COUNTIES UNTIL 515 PM CDT...
At 427 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles north of Rush Lake, or 9 miles northeast of Berlin, moving
northeast at 30 mph.
Local wind gusts in excess of 40 mph will be possible with this
storm. The storm is intensifying.
This strong thunderstorm will be near...
Oshkosh around 500 PM CDT.
Menasha around 515 PM CDT.
Other locations impacted by this storm include Butte Des Morts,
Highland Shore, Larsen, Lake Butte Des Morts, Winnebago, Rivermoor,
Winneconne, Harbor Springs, Medina and Clarks Point.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
If on or near a lake, get out of the water and move indoors or
inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.
&&
LAT...LON 4390 8876 4399 8889 4408 8889 4433 8864
4418 8840 4412 8840
TIME...MOT...LOC 2127Z 222DEG 17KT 4402 8878
RDMThe Green Bay radar (KGRB), 73 km away, was scanning. The volume nearest the first event began at 21:35 UTC.
3 tornado, 1 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds downed several trees in Omro and blew sheet metal off a score board at Omro High School. The time of this event is an estimate based on radar data.
A brief tornado touchdown was witnessed by the Oshkosh Fire Department near Highway 45 near Butte des Morts. No damage was reported.
A storm chaser and the public spotted a tornado over Lake Butte des Morts near County S. The tornado dissipated before reaching shore.
Multiple eyewitness reports of a tornado over Lake Winnebago 5 to 6 miles southeast of Oshkosh Wittman Field Airport. The tornado dissipated before reaching shore.
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, June 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: 889037, 889033, 889034, 889035.