The threat of storms was in the forecast from earlier in the week.
The set-up for a cold front colliding with warm humid air usually results in storms. FutureScan from 36 hours before the storms hit shows the cold front and where t-storms were expected, which for the most part was accurate.
The cap was strong, so the storms held off on developing until late evening. But once a few cells started developing in southwest Minnesota, storms started to unzip down the cold front, and it didn't take long for the storms to go from small cells to severe storms.
The storm over Sioux Falls was a supercell. These storms are notorious for producing damaging winds and large hail...even tornadoes under the right conditions. The severe thunderstorm warning issued for the storm was an alert for the impending threat the storm posed.
As it approached Sioux Falls, it had most of the classic features we identify with these storms. A hook echo can be seen west of Sioux Falls at 10:02pm shown here, with a trailing rear flank downdraft shown here with this fine line. These are strong, straight-line winds.
As the storm pushed through the city, the hail core took its path to the left of the hook, some of it nearly baseball in size. This follows the text book definition of these supercell storms.
Here are few pictures sent in from KELOLAND viewers. The biggest reports were centered on the city's central and south side.
The damage it left at the west side Target store is impressive, with a hole in the roof and much debris to clean up. More analysis may be done on this to take a look at exactly what happened in the Empire Mall area that resulted in the most intense damage.