Tornadoes:

Tornadoes - Northeastern WY and Southwestern SD Campbell, Crook, Fall River, and Oglala Lakota Counties Date June 12, 2001 Times (Local) 1:27, 1:30, 1:50, 2:35, 4:50, 5:05, 6:05, and 7:10 pm (end times unknown) F Ratings F0 to F1 Est. Peak Winds 110 mph Path Length Estimated 27 mi (max) Max Width 100 yards Injuries/Deaths 0 Summary: A local outbreak of eight tornadoes occurred across northeastern Wyoming and southwestern SD from 1:27 to 7:10 pm MDT. The strongest tornado was rated EF-1 and traveled 27 miles from southeastern Campbell into west-central Weston County, WY. Track Map

Tornado ratings are assigned based on the amount of damage they cause. The tornadoes in northeastern Wyoming and southwestern South Dakota were rated using the original Fujita tornado damage scale (http://www.spc.noaa.gov/faq/tornado/f-scale.html). In 2007, the National Weather Service began using the Enhanced Fujita (EF) scale (http://www.spc.noaa.gov/faq/tornado/ef-scale.html), which is an updated F-scale developed by a team of meteorologists and wind engineers.

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

Visibility was very good across northeastern Wyoming and the tornadoes were widely observed as they moved toward western South Dakota. 

Wall Cloud 10 miles west of Edgemont, SD, between 4:30 and 4:40 pm MDT (photo by Matt Bunkers)	Funnel cloud 10 miles west of Edgemont, SD, between 4:30 and 4:40 pm MDT (photo by Matt Bunkers)	Closer view of funnel cloud 10 miles west of Edgemont, SD, between 4:30 and 4:40 pm MDT (photo by Matt Bunkers)

Tornado at 6:05 pm MDT near the South Dakota/Nebraska border on US 385 (photo by Matt Bunkers)	Closer view of the tornado at 6:05 pm MDT near the South Dakota/Nebraska border on US 385 (photo by Matt Bunkers)

Radar

The storms began between noon and 1 pm south of Gillette, WY, and quickly became severe. While individual storms moved to the east or northeast, there was continual redevelopment of the storms to the south. Most of the storms across Wyoming decreased in intensity as they approached South Dakota and were no longer severe by the time they crossed the state line. However, those storms furthest to the south (near the extreme southwestern corner of South Dakota) were able to tap into a more unstable atmosphere and continued to produce tornadoes across Fall River and Oglala Lakota Counties of southwestern South Dakota.

Radar animation from 1:12 to 7:02 pm MDT on 12 June 2001

Environment

The weather conditions which produced this outbreak of tornadoes were very similar to other tornado events across this area. Surface low pressure was located over southeastern Wyoming, with a very unstable, and highly sheared atmosphere across the area. A surface front was draped from northeastern Wyoming across southwestern South Dakota, which may have helped to promote the formation of tornadoes this day.

Sounding for Rapid City at 6 am MDT 12 June 2001	Hodograph for Rapid City at 6 am MDT 12 June 2001

Surface dewpoint temperatures were fairly high across northeastern Wyoming around midday (below left), and by 3 pm MDT the dewpoints had reached the mid 60s in far southwestern South Dakota.

Surface map valid 12 pm MDT 12 June 2001	Surface map valid 3 pm MDT 12 June 2001