Sioux Falls, SD

Weather Forecast Office

August 18th 2017 Tornadic Supercell

Overview

A line of thunderstorms formed across portions of western Minnesota and eastern South Dakota during the late afternoon hours of Friday August 18th. These thunderstorms initially were capable of very large hail and damaging winds, with 67 mph winds measured in Minneota, MN.

While strong storms continued to move through Lake Shetek, it was a strong cyclic supercell that formed on the tail end of this line that become the main weather story. This supercell produce large hail and strong winds, but also became a prolific tornado producer with multiple tornadoes moving across far southern Minnesota and into Northwest Iowa during the evening hours.

Damage from these tornadoes was reported near Rushmore, MN, just west of Bigelow, MN, with the strongest tornado taking place further south near Melvin, IA. This tornado was rated EF-2 with peak winds of 125 mph. The following tabs will provide a look at the radar, photos, and tornado rated information for this event.

Radar Loop of the Event


Large Hail Near Wilmont, MN From Theresa Nequette	Tornado Near Bigelow, MN from Jill Heidebrink	Airplane Survey by Jordan E Grauer

Tornado
Wind & Hail
Radar
Storm Reports & Drone Survey

Tornadoes:

Tornado - Rushmore North of I-90


Flattened Corn North of Rushmore, MN	Damage to Hog Farm North of Rushmore, MN	Damage to Crops Near Rushmore, MN	Drone Captured Tornado Track

	Radar Near Rushmore, MN

Tornado - Rushmore South of I-90


Flattened Corn West of Rushmore, MN	Flattened Corn West of Rushmore, MN	Storm Rotation Near Rushmore, MN Via Doug Neyens	Tornado near Rushmore, MN from Laurie Berger DeNeui

Tornado - Bigelow, MN into Northern Iowa


Initial Touchdown Near Bigelow, MN	Rolled Grain Bin Near Bigelow, MN	Destroyed Garage Near Bigelow, MN	Tornado Near Bigelow, MN by Jill Heidebrink

Tornado - Near Melvin, IA


Snapped Trees Northwest of Melvin, IA	Damage to Farm Northwest of Melvin, IA	Farm Buildings Destroyed Northwest of Melvin, IA	Tornado Near Melvin, IA from Jenny Bosma

Destroyed Building and Rolled Truck Northwest of Melvin, IA	Flattened Corn Near Farmstead Northwest of Melvin, IA	Snapped Trees Near Farmstead Northwest of Melvin, IA	Snapped Trees Northwest of Melvin, IA

Radar At Peak Intensity West of Melvin, IA At 815 pm CDT

The Enhanced Fujita (EF) Scale classifies tornadoes into the following categories:

EF0 Weak 65-85 mph	EF1 Moderate 86-110 mph	EF2 Significant 111-135 mph	EF3 Severe 136-165 mph	EF4 Extreme 166-200 mph	EF5 Catastrophic 200+ mph

Wind & Hail:

Wind Damage and Storm Structure Photos

Wind damage, outside of related to tornadic activity was limited with these storms. Here is a look at various storm structure pictures from this event.


Storm Near Bigelow, MN	Storm Near Brewster, MN from Chad Cummings	Storm Structure Near Little Rock from Nicole Jeeninga	Storm Near Melvin, IA From a Distance

Tree Damage From Dickinson County EMA	Overturned Semi from Dickinson County EMA

Hail

Several storms produced large hail anywhere from dime size all the way to baseball sized. Here is a look at hail pictures from across Southwest Minnesota and Northwest Iowa from August 18th.


Hail Near Rushmore, MN from Brandy Darling Harberts	Small Hail Unknown Location from Jes Hermeling	Hail Near Bigelow, MN from Staci Cauwels	Large Hail Near Wilmont, MN from Theresa Nequette

Shredded Soybeans, Unknown Location from Jes Hermeling	Large Hail Near Bigelow, MN	Large Hail Near Bigelow, MN from Tara Svalland	Large Hail Near Sibley, IA from Josh Harms

Radar:

Regional Radar Presentation and Individual Images of Tornado Supercells.


Low Level Rotational Tracks	Hail Tracks	Supercell Tracking Near Rushmore, MN	Supercell Tracking From Bigelow, MN to Melvin, IA.

Tornado Debris Signature Near Melvin, IA

Storm Reports & Drone Survey

Thanks to our partners at the Dickinson County EMA, here is a collection of photos taken by a drone during our survey.

Here is a look at storm reports from the Sioux Falls Forecast area.

Report Time	Location	ST	Event Type	Mag.	Source	Remark
Fri Aug 18 2017 22:35:00 GMT-0500 (Central Daylight Time)	Minneota	MN	TSTM WND GST	67	storm chaser	winds gusting to 67 mph in minneota along with pea size hail and torrential rain.
Fri Aug 18 2017 22:54:00 GMT-0500 (Central Daylight Time)	1 E Lake Benton	MN	HAIL	1	trained spotter
Fri Aug 18 2017 23:00:00 GMT-0500 (Central Daylight Time)	Lynd	MN	HAIL	1	storm chaser	quarter size hail and widespread road flooding reported in lynd via social media.
Fri Aug 18 2017 23:25:00 GMT-0500 (Central Daylight Time)	Garvin	MN	TSTM WND GST	60	trained spotter	trained storm spotter estimated winds gusting to 60 mph.
Fri Aug 18 2017 23:40:00 GMT-0500 (Central Daylight Time)	8 NNE Jeffers	MN	HAIL	1	public
Fri Aug 18 2017 23:45:00 GMT-0500 (Central Daylight Time)	Lake Wilson	MN	TSTM WND GST	60	co-op observer
Fri Aug 18 2017 23:45:00 GMT-0500 (Central Daylight Time)	Lake Wilson	MN	HAIL	1	co-op observer	pea to quarter size hail.
Sat Aug 19 2017 00:20:00 GMT-0500 (Central Daylight Time)	2 S Wilmont	MN	HAIL	1.5	trained spotter
Sat Aug 19 2017 00:26:00 GMT-0500 (Central Daylight Time)	3 NW Rushmore	MN	TORNADO	0	nws storm survey	ef1 tornado traveled 1.6 miles with a 50 yard wide path. the tornado lifted at 7:35 just southwest of rushmore.
Sat Aug 19 2017 00:26:00 GMT-0500 (Central Daylight Time)	3 NW Rushmore	MN	TORNADO	0	nws storm survey	tornado traveled 1.6 miles with a 50 yard wide path. the tornado lifted at 7:35 just southwest of rushmore.
Sat Aug 19 2017 00:40:00 GMT-0500 (Central Daylight Time)	5 SW Worthington	MN	HAIL	1.75	public
Sat Aug 19 2017 00:46:00 GMT-0500 (Central Daylight Time)	NW Rushmore	MN	TSTM WND DMG	0	law enforcement	hog barn destroyed.
Sat Aug 19 2017 00:47:00 GMT-0500 (Central Daylight Time)	1 W Bigelow	MN	TORNADO	0	nws storm survey	ef1 tornado traveled 1.97 miles with a 100 yard wide path. the tornado lifted at 7:54 about a mile southwest of bigelow.
Sat Aug 19 2017 00:47:00 GMT-0500 (Central Daylight Time)	Bigelow	MN	TORNADO	0	nws storm survey	ef1 tornado traveled 1.97 miles with a 100 yard wide path. the tornado lifted at 7:54 about a mile southwest of bigelow.
Sat Aug 19 2017 00:55:00 GMT-0500 (Central Daylight Time)	Bigelow	MN	HAIL	2	broadcast media
Sat Aug 19 2017 01:07:00 GMT-0500 (Central Daylight Time)	5 NW Melvin	IA	TORNADO	0	nws storm survey	ef2 tornado traveled 6 miles with a 250 yard wide path. the tornado lifted at 8:27 about a 1/2 mile southwest of melvin.
Sat Aug 19 2017 01:14:00 GMT-0500 (Central Daylight Time)	3 S Bigelow	IA	TSTM WND DMG	0	public	tractor trailer overturned on highway 60.
Sat Aug 19 2017 01:30:00 GMT-0500 (Central Daylight Time)	4 E Primghar	IA	HAIL	1.75	broadcast media	broadcast media relay of a public report.
Sat Aug 19 2017 01:41:00 GMT-0500 (Central Daylight Time)	2 W Hartley	IA	HAIL	1	trained spotter
Sat Aug 19 2017 01:50:00 GMT-0500 (Central Daylight Time)	2 NW Melvin	IA	TSTM WND DMG	0	emergency mngr	farmstead damaged. no injuries.

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