Hail, EF1 Tornado, Winds Hit the Big Horn Basin Monday 08/30/10 - Updated 9/7

Supercell Thunderstorm with EF1 Tornado Hits West-Central Big Horn Basin Monday August 30, 2010

In the afternoon of Monday August 30, 2010, a supercell thunderstorm developed over the central Big Horn Basin in Wyoming, and moved ENE toward the Ten Sleep area.  Shortly after development just west of Lucerne, ping pong ball size hail was reported two miles NNE of Lucerne.  This hail fell at approximately 1250 PM MDT and was also noted at the intersection of Nakamura Lane and Highway 20.  Damage appeared to be confined to trees and plants, with some small dents in metal roofs and vehicle hoods.

The storm increased in intensity as it moved into the "badlands" - an extremely unpopulated deseret-like area of the southeast Big Horn Basin.  The storm moved in a ENE direction and skirted the south side of Worland by a few miles.  By 130 PM MDT, the storm did manage to produce 25 MPH gusts at the Worland airport along with depositing 0.11" of rain - no hail was reported.

At approximately 150 PM MDT, the storm became more intense and generated a tornado.  The following images show the tornado when it was approximately five miles southwest of Ten Sleep.  The first picture is courtesy of Gary O'Donnell, who took this image from about six miles north of Ten Sleep.  The second image is courtesy of Chris Christenson and Gail Wagner of Worland.  It was taken from Highway 16 west of Ten Sleep looking south.  The third image is of damage done to Juniper bushes/trees on the ridgeline to the west of the No Wood River Valley.  It is courtesy of Bill Hill and Don Clark of Worland who made their own damage survey in the hills about five miles southwest of Ten Sleep.

Ten Sleep Tornado Gary O'Donell Augst 30, 2010

Chris Christenson Ten Sleep Tornado August 30, 2010

Bill Hill Ten Sleep Tornado Juniper damage

Based on a damage survey of residences and ranches south of Ten Sleep conducted by Brett McDonald, Science and Operations Officer, it is believed that the tornado descended the ridge into the No Wood River valley two to three miles south of Ten Sleep.  This occurred right around 200 PM MDT.  However, the storm was beginning to weaken and the tornado began to "pull" back up into the supercell at about Highway 434.  Damage in the area was consistent with 80 to 100 MPH winds.  On the north end of the damage zone (Cheeney residence), the tornado is believed to be the causal factor as numerous cottonwood trees sustained significant damage and several well-built out buildings were destroyed.  On the south end of the damage area, it is believed that an enhanced rear flank downdraft created the incredibly strong winds.

Brett McDonald Ten Sleep Tornado Cheeney out building

Further to the south at the Smith and Bodtke ranches, it is believed that 80+ MPH south winds on the south side of the storm caused the majority of the damage.  A very large cottonwood tree fell onto the well-constructed Smith garage and others fell around the ranch.

Brett McDonald Ten Sleep Tornado Smith Garage

At the Bodtke ranch, numerous trees were down and substantial damage was done to the sorghum crop.  Mr. Bodtke noted very strong winds from the south, ping pong ball size hail, and then very strong winds from the west.  Several windows and vinyl rain gutters were shattered.

Several residences in the area also sustained substantial damage as a result of the wind blown hail.  The Evans residence right on Highway 434 had the front double-pane windown shattered and blown inside.  The following image is the south facing exterior wall of the Daugherty residence where hail literally beat up the vinyl siding and broke a couple of windows.

Brett McDonald Ten Sleep Tornado Daugherty Siding

At the Boltz residence, metal roofing was stripped off the garage and thrown several hundred yards away.

Brett McDonald Ten Sleep Tornado Boltz Garage


The Google map below indicates the locations of the surveyed damage.  Also indicated are the approximate locations of the tornado based upon WSR-88D radar data from the Riverton, WY radar.  It must be noted that the lowest  level radar beam to sample this storm was about 8000 ft AGL in this area.

Ten Sleep Tornado Google Map


Based on data collected by and reported to the Riverton, WY National Weather Service, this tornado has been rated an EF1 on the Enhanced-Fujita scale (click here for more information).  Again, the damage on the northern half of the area is attributed to the tornado, while damage in the sourther half of the area is attributed to very strong straight-line winds caused by the read flank downdraft as the supercell was collapsing.

The following are images of radar data from the Riverton Doppler radar.  All images are from data at approximately 156 PM MDT.

Composite Reflectivity:

Ten Sleep Tornado Comp Refl KRIW 1956UTC

Base Reflectivity (0.5):

Ten Sleep Tornado Base Refl 0.5 1956UTC

Base Velocity (0.5):

Ten Sleep Tornado Base Velocity 0.5 1956UTC


More infomartion regarding this event will be included next week.  For questions or comments, please contact Brett McDonald, Science and Operations Officer, at brett.mcdonald@noaa.gov.

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