Damage Survey of Ethan, SD for June 20, 1997

During the early morning hours of Friday, June 20^th severe thunderstorms moved across a portion of eastern South Dakota. These severe thunderstorms caused widespread damage of downed trees & power lines, damaged buildings and destroyed crops. Some the damage was quite severe resulting in eight injuries in and around the Ethan area. This paper discusses the damage that resulted from the severe storms that affected Ethan.

On June 20^th, a severe thunderstorm warning was issued at 413 am cdt for Davison county. This warning was valid until 445 am cdt and provided a "pathcast" of when & where the storm was forecast. The pathcast mentioned the storm would affect the town of Ethan at 440 am cdt. Reports of tree and building damage in the vicinity of Ethan were first received at 451 am cdt from the Davison county emergency manager, Alan Miller. This report was followed by numerous other reports from the media, as well as the public. Alan Miller later followed up his initial report with succeeding reports of tree and building damage. Based on his training, he concluded the damage was a result of strong straight-line winds. However, the public in the Ethan vicinity was stating to the media that tornado struck the area, so it was decided a National Weather Service (NWS) damage survey should be conducted as soon as possible. Later that morning, NWSFO Sioux Falls Warning Coordination Meteorologist, Todd Heitkamp, was dispatched to Davison county to make an "official" determination of what caused the damage, a tornado or strong straight-line winds.

After exiting I-90 and driving south on SD Highway 27 for six to eight miles, damage to trees and downed power lines was first noticed. The area of the damage was approximately a quarter of mile wide, but continued to the east as far as the eye could see. All the trees and power poles were laying to the east. As I entered the town of Ethan, widespread tree and building damage was visible. Large trees were uprooted and numerous branches were broken with this debris all thrown to the east. Buildings that were open to the west were severely damaged. One storage shelter was destroyed with all of the pieces of the shelter laying head to tail and pointing to the east. Leaves were "pasted" on the west faces of buildings with nothing on the other sides of the buildings. This was caused by strong west winds blowing the wet leaves against the homes. The Ethan lumber yard received extensive damage, as much of the lumber was free and able to become projectiles. All of the debris from the lumber yard was laying to the east. To the west of lumber yard is a grain elevator. The grain elevator itself received little damage, but a storage building close to the elevator, oriented north-south, had an indentation on the westward or windward side. This was caused either by flying debris or the strong wind itself. Crops immediately surrounding Ethan and elsewhere were also severely damaged. The damaged crops and the weeds in the ditch were all laying to the east. Even round hay bails were pushed in an eastward direction and some of the hay was torn from the bails which resulted in a hay trail in many fields. This trail was oriented northwest to southeast.

After looking at the damage within Ethan, I went to inspect the damage that occurred to a mobile home where five people were trapped for a period of time. The mobile home was approximately 2 miles west and 1 miles north of Ethan. The mobile home was totally destroyed trapping the residents for over an hour. Injuries were received by all inside the residence. I was not able to do a close inspection of the damage due to the access road being roped off by the family. But from the road, I was able to determine that the mobile home was unsecured and was sitting on cinder blocks. All the debris was thrown to the east with some pieces of the structure laying a half mile away from its original location. Upon close inspection of the immediate vicinity of the residence, no tornadic tracks, caused by suction vortices, were visible in the fields. Therefore the debris pattern was consistent with the others.

I then went 10 to 15 miles east of Ethan to see the damage to the Oak Lane Colony. On the way, many farms and grain bins were damaged. The grain bins that were damaged were empty, so there was nothing supporting the walls of the bin. At the Oak Lane Colony, many buildings were damaged and some destroyed. The turkey feed operation buildings, as well as un-anchored storage buildings received extensive damage. The more securely fastened buildings, such as their homes only received cosmetic damage.

After completing the damage survey, in my professional judgment, the damage throughout Davison and western Hanson counties was a result of strong straight line winds of 80 to 90 mph. With tornadic damage, the debris is most often thrown in all directions. This type of pattern was not visible. The areas that received damage were too wide to have been caused by a tornado. The damage path was as wide as 15 miles and as long as 50 miles. The only thing that could cause this widespread of damage would be strong straight line winds. This conclusion is also supported by the data gathered by the NWS Doppler radar. I know many residents of Ethan feel a tornado hit their town. I understand their feelings, but we must remember that tornadoes are not the only weather phenomena that can cause major destruction.

Author: Todd Heitkamp

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BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE SIOUX FALLS SD
413 AM CDT FRI JUN 20 1997

* SEVERE THUNDERSTORM WARNING FOR
  DAVISON COUNTY IN SOUTHEASTERN SOUTH DAKOTA

* UNTIL 445 AM CDT

* SOME AREAS AFFECTED
  MT VERNON AROUND 415 AM CDT
  LOOMIS AROUND 430 AM CDT
  MITCHELL AROUND 435 AM CDT
  ETHAN AROUND 440 AM CDT

* AT 412 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
  A LINE OF SEVERE STORMS 16 MILES WEST OF MITCHELL OR 4 MILES WEST OF
  MT VERNON MOVING EAST AT 35 MPH.

WHEN THUNDERSTORMS ARE OCCURRING...PEOPLE SHOULD MOVE INSIDE A STRONG
BUILDING. DO NOT STAND BY WINDOWS. DO NOT USE TELEPHONES OR ELECTRICAL
APPLIANCES UNTIL THE STORM HAS PASSED UNLESS IN AN EMERGENCY. MOTORISTS
SHOULD NOT DRIVE INTO LOW WATER CROSSINGS.

RUBY