June 12, 2001 Tornadoes

Northeastern Wyoming and Southwestern South Dakota - During the afternoon of June 12th, a series of supercell thunderstorms produced more than 14 tornadoes across northeastern Wyoming and southwestern South Dakota. Fortunately,  only isolated areas of damage were reported from these storms. Check out the radar animation.

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. Visibility was very good across northeast Wyoming, and the tornadoes were widely observed as they moved toward western South Dakota. 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 southwest corner of South Dakota) were able to tap into a more unstable atmosphere and continued to produce tornadoes across Fall River County of southwestern South Dakota.

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 southeast Wyoming, with a very unstable, and highly sheared atmosphere across the area. A surface front was draped from northeast Wyoming across southwestern South Dakota, which may have helped to promote the formation of tornadoes this day.

Wall Cloud 10 Miles West of Edgemont, SD
Wall Cloud 10 miles west of Edgemont, SD between 4:30 PM and 4:40 PM MDT

Funnel Cloud 10 Miles West of Edgemont, SD
Funnel Cloud 10 miles west of Edgemont, SD between 4:30 PM and 4:40 PM MDT

Funnel Cloud 10 Miles West of Edgemont, SD
Funnel Cloud 10 miles west of Edgemont, SD between 4:30 PM and 4:40 PM MDT

Tornado near SD/NE/US 385 Border
Tornado at 605 PM MDT near the South Dakota/Nebraska border on US 385

Tornado Near SD/NE/US 385 Border
Tornado at 605 PM MDT near the South Dakota/Nebraska border on US 385

Location Map

June 12, 2001 Tornado Track Map
The green mark is the mesocyclone track. The "T" is where tornadoes were reported.

What is a Mesocylone?

A mesocyclone is a storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an HP storm). The circulation of a mesocyclone covers an area much larger than the tornado that may develop within it.

Properly used, mesocyclone is a radar term; it is defined as a rotation signature appearing on Doppler radar that meets specific criteria for magnitude, vertical depth, and duration. Therefore, a mesocyclone should not be considered a visually-observable phenomenon (although visual evidence of rotation, such as curved inflow bands, may imply the presence of a mesocyclone).

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