Tornadoes · United States · Wisconsin · 2021

EF1 tornado, Stinson to Drephal, Wisconsin, August 10, 2021

Name: EF1 tornado, Stinson to Drephal, Wisconsin, August 10, 2021
Start: 2021-08-10T22:58:00.000Z
End: 2021-08-10T23:11:00.000Z
Location: Stinson to Drephal, Wisconsin

From Stinson to Drephal, this EF1 tornado ran 2.0 miles across Outagamie County on August 10, 2021, touching down at 5:58 PM CDT and reaching 40 yards wide. It killed nobody.

The rating scale

Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

EF065 to 85 mph
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mphthis tornado
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
EF2111 to 135 mph
Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.
EF3136 to 165 mph
Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.
EF4166 to 200 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
EF5over 200 mph
Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.
Unrated
The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

The record

Rating: EF1
Date: August 10, 2021
Touchdown: 5:58 PM CDT (22:58 UTC)
Lifted: 6:11 PM CDT (23:11 UTC)
On the ground: 13 minutes
Path length: 2.0 miles (3.3 km)
Path width: 40 yards (37 m)
Deaths: 0
Injuries: 0
County: Outagamie County
Touchdown point: 44.538, -88.530
Lift-off point: 44.530, -88.491
Record number: 2108101658-01

What the Weather Service recorded

Thunderstorms developed ahead of an outflow boundary during the evening hours across east-central Wisconsin. The strongest storms produced damaging winds and a tornado. Rainfall amounts around 2 inches fell in Green Bay, producing flash flooding.

A tornado formed at 5:58 pm CDT northwest of Black Creek in Outagamie County and continued east southeast before dissipating at 6:11 pm CDT. The tornado produced damage to trees (DI 28, DOD 2,3,4) and to the siding and roof to a house (DI 2, DOD 2). Total path length is estimated to be 2.05 miles long, with a width of 40 yards. Peak wind estimated to be around 90 mph.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

The warnings

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down. One was issued for the county at another hour that day.

The county was under a severe thunderstorm watch, issued at 20:48 UTC and running to 01:12 UTC.

Issued (UTC)	Expired	Product	Office
20:48 UTC	01:12 UTC	Severe Thunderstorm Watch	GRB
23:00 UTC	23:30 UTC	Tornado Warning	GRB
23:29 UTC	00:01 UTC	Severe Thunderstorm Warning	GRB
23:52 UTC	03:00 UTC	Flood Advisory	GRB

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The forecast that day

The Storm Prediction Center had this point in a Slight Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 19:54 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The air that afternoon

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

Green Bay/Straub, WI (KGRB), 12:00Z

11.0 hours before the tornado, 33 km from the path. August 10, 2021.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.

Mixed-layer CAPE: 32 J/kg
Mixed-layer CIN: -550 J/kg
Surface CAPE: 0 J/kg
Mixed-layer LCL: 828 m above ground
0-6 km bulk shear: 16 kt
0-1 km bulk shear: 9 kt
0-1 km storm-relative helicity: 42 m²/s²
0-3 km storm-relative helicity: 117 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0
0-3 km lapse rate: 2.4 K/km

Open this sounding in Storm Lab

The radar

The Green Bay radar (KGRB), 32 km away, was scanning. The volume nearest the touchdown began at 23:00 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

What was reported nearby

Local storm reports within 60 km of the path, in the three hours either side.

Time (UTC)	Report	Where	County	Remark
22:57 UTC	FUNNEL CLOUD	3 Sw Nichols	Outagamie, WI
23:02 UTC	TORNADO	2 Sw Nichols	Outagamie, WI	CORRECTS PREVIOUS TORNADO REPORT FROM 2 SW NICHOLS. TORNADO MAY HAVE TOUCHED DOWN EARLIER PENDING STORM DAMAGE SURVEY RESULTS.
23:02 UTC	TORNADO	2 Sw Nichols	Outagamie, WI
23:03 UTC	FUNNEL CLOUD	2 N Black Creek	Outagamie, WI
23:18 UTC	FUNNEL CLOUD	2 N Black Creek	Outagamie, WI	CORRECTS TIME FOR PREVIOUS REPORT.
23:41 UTC	HAIL 0.5	4 Wsw Green Bay	Brown, WI	REPORTED VIA SOCIAL MEDIA.
23:49 UTC	TSTM WND DMG	1 Se Green Bay	Brown, WI	TREES DOWN ON THE EAST SIDE OF GREEN BAY. TIME ESTIMATED BY RADAR. REPORT VIA SOCIAL MEDIA.
23:51 UTC	TSTM WND DMG	3 E Green Bay	Brown, WI	REPORT OF A TREE FALLING ON A HOUSE. REPORT VIA SOCIAL MEDIA. TIME ESTIMATED BY RADAR.
23:51 UTC	TSTM WND DMG	3 S Green Bay	Brown, WI	MULTIPLE TREES DOWN IN ALLOUEZ AND BELLEVUE. THE TIME OF THIS REPORT IS AN ESTIMATE BASED ON RADAR.
00:05 UTC	TSTM WND GST 47	Oshkosh	Winnebago, WI
00:12 UTC	FLOOD	2 Nne Ashwaubenon	Brown, WI	UP TO 4 INCHES OF WATER FLOWING DOWN ONEIDA STREET. INTERMITTENTLY FROM PILGRIM WAY TO NEAR LAMBEAU FIELD.
00:18 UTC	TSTM WND DMG	3 E Green Bay	Brown, WI	REPORT OF A TREE FALLING ON A HOUSE. REPORT VIA SOCIAL MEDIA.
00:23 UTC	FLOOD	1 Wnw Green Bay	Brown, WI	FLOODING REPORTED NEAR THE INTERSECTION OF CROOKS STREET AND KURTZ AVENUE.
01:00 UTC	FLOOD	Bellevue	Brown, WI	STREET FLOODING REPORTED AT TUNIS RD AND HELSINKI RD, HELSINKI RD AND OSLO DR, AND SERVANT WAY.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

This ground now

The live radar over the track Every 2021 tornado in Wisconsin Every tornado in Wisconsin since 1950 Warnings in force in Wisconsin now The forecast where you are

The other tornadoes of August 10, 2021

3 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Damage
August 10	4:43 PM CDT	EF0	Hodgeman, KS	0.2	50
August 10	5:50 PM EDT	EF0	Pasco, FL	0.1	25	$10,000
August 10	6:33 PM CDT	Unrated	DeKalb, IL	0.6	20

What this means

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

Sources

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.