Storm Survey for Southeast South Dakota - May 29, 2008

Tornado Reports

Hail Reports

Wind Reports

Radar imagery of the tornadic supercell near Irene, South Dakota.

The most concentrated area of damage was around Irene and Centerville, South Dakota.  Much of this damage occurred around 7:10 pm CDT.  One tornado and several reports of wind damage were received in this area including trees and power lines down as well as damage to outbuildings on a farmstead. 

The radar picture below shows some common signatures seen with tornadic supercells.  In the upper left corner of the picture is how the storm looked approximately 4000 ft above the ground.  To the south of Irene, one can see a "bulge" in the radar echo as it moves toward Wakonda, SD.  This is indicative of strong outflow winds from a rear flank downdraft.  A rear flank downdraft is rapidly sinking area of air on the south side of a supercell.  It is indicative a strong mesocyclone, or rotation, and can contain wind speeds in excess of 60 mph.  It is likely that the damage in Wakonda was the result of these winds.

In the cross-section in the lower left corner of the figure, one sees two common features in supercells.  The first is a bounded weak echo region.  This is an area of rapidly rising air and is also the center of rotation within a supercell thunderstorm.  The second is the elevated hail core located above the bounded weak echo region (and updraft).  Tornadoes typically occur in the vicinity of the bounded weak echo region.  This is also where the large and destructive hail within supercells is produced.  In this case, up to 1.75 inch hail (golf ball size) was reported in Irene.

Damage path and photos from a NWS Damage Survey of a tornadic supercell that moved across northeast Clay County, South Dakota

The tornadic supercell that moved across northern Clay County between 7:00 pm and 7:30 pm CDT produced two EF1 tornadoes south of Highway 46 near Wakonda, South Dakota.  Based upon the survey, it as determined there was an area of 60 to 70 mph winds that produced tree damage along Highway 46 into Centerville, South Dakota.  In addition to the winds, two EF1 tornadoes (wind speeds of 86 - 110 mph) developed in northwestern Clay County.  The first tornado was located approximately 3 miles west Wakonda and the second tornado developed 2.5 miles north of Wakonda.  Both tornadoes moved to the northeast and had a path length of approximately 2 miles. 

Map of the tornado paths from two EF1 tornadoes in Clay County, SD.

Description and location of wind damage along Highway 46 in South Dakota.

Damage to an outbuilding from damaging winds approximately 3 miles west of Wakonda, SD.

EF1 tornado damage to an outbuilding of a farmstead approximately 4 miles north-northeast of Wakonda, SD.