Twin Cities, MN

Weather Forecast Office

Sept 20 Tornadoes and Damaging Winds

Overview

A line of thunderstorms developed the evening of September 19th across the eastern Dakotas and moved into western Minnesota before midnight of September 20th. Severe thunderstorms developed into west central and parts of central Minnesota producing large hail, downbursts and six tornadoes. This line of thunderstorms slowly weakened as it moved into far eastern Minnesota, with general, non-severe thunderstorms as the line progressed into West Central Wisconsin after 3 am CDT.

Tornado, Downburst, and Indeterminate Damage Points

Tornado
Photos & Video
Radar
Storm Reports
Environment

Tornadoes:

Tornado #1
Chippewa County

Date	9/20/2017
Time (Local)	12:18 AM - 12:20 AM CDT
EF Rating	EF-1
Est. Peak Winds	88 mph
Path Length	2.1 miles
Max Width	100 yards
Injuries/Deaths	None
Summary: The tornado began on the Chippewa County side of the Minnesota River, just east of the golf course. It moved east-northeast across the south side of Montevideo. Most of the damage was to trees, but siding and shingles were taken off a few homes and the Montevideo Community Center.

Track Map

Track Map

EF-Scale

Tornado #2
Swift and Kandiyohi Counties

Date	9/20/2017
Time (Local)	12:28 AM - 12:39 AM CDT
EF Rating	EF-1
Est. Peak Winds	90 mph
Path Length	12.6 miles
Max Width	550 yards
Injuries/Deaths	None
Summary: This tornado touched down in a corn field and moved northeast across many fields. It hit a church, several farms and a restaurant. Three of the farms were particularly hard hit, losing grain bins and machine sheds.

Track Map

Tornado #3
Swift and Pope Counties

Date	9/20/2017
Time (Local)	12:32 AM - 12:39 AM CDT
EF Rating	EF-1
Est. Peak Winds	100 mph
Path Length	9.2 miles
Max Width	880 yards
Injuries/Deaths	None
Summary: This tornado touched down in a field and moved northeast from Swift County into Pope County. It tore through a number of fields, hit several farms, and hit homes on the east side of Camp Lake. The worst damage was at Camp Lake, where outbuildings were demolished, a mobile home was rolled, and a modular home sustained heavy damage.

Track Map

Tornado #4
Stearns County

Date	9/20/2017
Time (Local)	12:48 AM-12:49 AM CDT
EF Rating	EF-0
Est. Peak Winds	75 mph
Path Length	1.2 miles
Max Width	330 yards
Injuries/Deaths	None
Summary: The tornado touched down on the northwest edge of Belgrade and moved east-northeast across the northern edge of town. It damaged dozens of trees and blew a shed across the street. There were many trees down around the rest of Belgrade due to downburst.

Track Map

Tornado #5
Stearns County

Date	9/20/2017
Time (Local)	12:49 AM - 12:56 AM CDT
EF Rating	EF-1
Est. Peak Winds	95 mph
Path Length	8.2 miles
Max Width	360 yards
Injuries/Deaths	None
Summary: This tornado touched down in a field and soon hit a farm, destroying several outbuildings. It moved through numerous fields, and hit three more farms and destroyed more sheds.

Track Map

Tornado #6
Todd County

Date	9/20/2017
Time (Local)	1:04 AM - 1:11 AM CDT
EF Rating	EF-1
Est. Peak Winds	95-100 mph
Path Length	6.8 miles
Max Width	440 yards
Injuries/Deaths	None
Summary: This tornado touched down just east of Big Swan Lake, where it hit one house, then moved across the northern end of Long Lake, hitting more homes, then after moving over fields and woods, hit the eastern end of Little Swan Lake, including the community of Pillsbury. More homes were damaged, including one that was pushed off its foundation. After leaving Pillsbury, the tornado moved through more fields and woods. It dissipated just as it reached the Todd-Morrison County line, about two miles north of Swanville. Downburst damage hit Swanville and areas north of Swanville.

Track Map

Tornado #7
Chippewa, MN County

Date	9/20/2017
Time (Local)	12:22 AM - 12:23 AM CDT
EF Rating	EF-1
Est. Peak Winds	90 mph
Path Length	0.1 miles
Max Width	80 yards
Injuries/Deaths	None
Summary: This tornado uprooted or snapped dozens of trees south of Montevideo and just east of the Minnesota River.

Track Map

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

Photos & Video:

Photos of Damage


Corn Damage 4 Miles West of Elrosa, MN	Damage 4.5 Miles West of Elrosa, MN	Damage to the Northeast of Camp Lake, MN	Trees Uprooted 5.5 Miles West of Sunburg, MN

Radar:

Header

Radar reflectivity (left) and storm relative velocity (right) loop of tornadic storm across West Central Minnesota from 12:02 am CDT through 1:13 am CDT.

Storm Reports

Click link to see storm reports for September 20, 2017: http://www.spc.noaa.gov/exper/archive/event.php?date=20170919

Environment

A strong and potent upper level disturbance in combination with a cold front acted as the forcing mechanisms for thunderstorm development. The environment in Western Minnesota during the early morning hours of September 20, 2017 was favorable for severe thunderstorm and tornado development as it was unstable with nearly 1000 J/kg of mixed layer CAPE and had plenty of wind shear with about 60 kt of 0-6 km shear.


Figure 1: Surface Observations at 1 AM CDT	Figure 2: 850 mb Analysis at 1 AM CDT	Figure 3: 500 mb Analysis at 1 AM CDT


Figure 4: Mixed Layer Cape and Mixed Layer CIN at 1 AM CDT	Figure 5: Effective Bulk Shear at 1 AM CDT	Figure 6: MPX Sounding at 1 AM CDT

Additional environmental data.

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