Target Area: Sioux Falls, South Dakota to Redwood Falls, Minnesota
Chase Area: Pipestone/Walnut Grove/Worthington, Minnesota to Sibley, Iowa
Observations: about three wall clouds, one supercell, squall line, lightning, flash flooding, two deer, and more fireflies than I'd ever seen before
Distance: 715 miles
Time: 15.5 hours
Chase Team: Jeff Makowski and myself
SPC Convective Outlook: Moderate Risk (Click to see SPC products, data, and storm reports)
Chase Setup: A weak shortwave trough and 500 mb jet streak were located over the eastern Dakotas. A surface low was centered over southeast South Dakota with a warm front extending eastward through southern Minnesota and a cold front draped southwestward from the surface low across southeast South Dakota and northern Nebraska. Surface dewpoints were in the low 70s in southern Minnesota and southeast South Dakota. MLCAPE ranged from 2000 to 3000 J kg-1 in southeast South Dakota and southwest Minnesota. Effective SRH was around 100 m2 s-2 in far southeast South Dakota and as high as 450 m2 s-2 in portions of southern Minnesota.
Chase Log: We left North Platte, Nebraska at about 10 am, and headed north on Highway 83. We briefly stopped in Thedford, to fill up the tank and take a few photos of the Doppler radar. We later found that there were two or three landpouts seen in that very spot just a few hours after we passed through.
In South Dakota, we got on I-90 eastbound and drove all the way to Minnesota. The threat for tornadoes kept shifting further east, so we wound up going much farther than we'd hoped. No sooner did we arrive in the land of rolling corn fields and dairies than we spotted a storm and began to head north.
We intercepted the supercell near Pipestone, and chased the quickly growing cells to Walnut Grove, at which point the storms had almost completely lined out. We were nearly forced to drive under a rotating wall cloud as we hurried south to get away from the advancing line of tornado-warned cells and large hail.
After playing with the squall line for a while, we decided to stop in Worthington for dinner. After dinner, we drove around town and noticed several roads were flooded with several inches of rain from the squall line. We watched a number of people drive through the flooded intersections anyway, and then decided to start going south again as we thought we saw an interesting, low-hanging cloud lit up by lightning.
We followed the line down into Sibley, Iowa, where we were ultimately diverted by a policeman as the town had just been hit by an EF4 tornado and the road was closed down. We ended the day in Sioux City, Iowa.