Northeast Iowa Supercell
Todd Shea, Warning Coordination Meteorologist
Dave Schmidt, Meteorologist
Staff members of the La Crosse National Weather Service surveyed damage left behind from a supercell thunderstorm that crossed through northeast Iowa wednesday evening.
The storm moved through Chickasaw county...northeast through Winneshiek county...and into the Waukon Iowa area in Allamakee county before crossing into southwest Wisconsin.
SRM: storm relative motion...used to indicate rotations in storms.
A pole barn owned by Protivin Builders Inc was destroyed about 1 mile southwest of Protivin by wind gusts of 80 to 100 mph. Debris from the barn was blown downwind...to the southeast...about 3/4 of a mile in open fields. It appears doors facing west gave way allowing the wind to get inside the building destroying it...while other nearby buildings were untouched...and supplies in the yard were left untouched.
There was minor damage to a nearby farmers mill as well. People there observed large hail...following by strong wind and rain. They saw no tornado and sheet metal was blown to the southeast...in one direction. The large hail started approx. 655 pm and the wind hit shortly after 700 pm.
Over three inches of rain fell north of Protivin...while under a quarter inch fell to the south.
All this damage appeared to be caused by straight line winds.
There was no damage noted or found from winds or tornadoes in Winneshiek county.
Considerable runoff from heavy rain caused erosion and damage to roads...especially east of Decorah. There was evidence of flash flooding although most of the water levels had clearly receded.
Several buildings at the UBC lumber yard on the south side of Waukon had roof damage...with sections of roof thrown downwind...to the southeast. Some sheds and supplies in the lumber yard were also shifted to the east or southeast. The storm hit between 800 and 815 pm and appears to be straight line wind. Significant water damage was reported to the main building...with at least 1 inch of standing water.
Along highway 76...just southeast of Waukon...a farm was hit by a small tornado that damaged part of the house and at least one outbuilding. Shingles from other buildings were embedded around the base of the house...and mud was noted on the south side of the house...even though most of the debris was blown to the east and southeast.
The tornado hit around 815 pm and people interviewed heard the warning via television. In fact...they left a nearby mobile home to a better structure. This tornado will be ranked an f0 with a diameter of 20 yards and a length of 1/8 of a mile.
A barn was also demolished another 1/2 mile southeast but this damage appears to be from straight line wind...perhaps with the rear flank downdraft around the tornado. Debris was thrown to the southeast.
Other isolated tree damage was noted east of Waukon...along County Road A52. Most of this area also suffered significant water runoff or flash flooding Wednesday evening as well.
Damage to a pole barn southwest of Protivin, IA. Note debris blown to the southeast.
Damage at Protivin Builders Inc. just southwest of Protivin.
Pole barn demolished near Protivin.
House damaged from a brief tornado touchdown just south of Waukon, IA, along Highway 76.
Old barn demolished southeast of Waukon, IA from strong wind gusts.
Damage near Protivin, IA.
Damage to UBC Building Center on south side of Waukon, IA from strong winds.
Northwest Buffalo county, WI Supercell
Randy Breeser, DAPM