Tornado Threat Turns Linear

Tuesday, July 2, 2024 dawned with a significant chance of severe weather possible for most of the state of Iowa. Mesoscale Discussion 1511 (above left) posted the probability of wind, hail and tornadoes in southern and southeastern Iowa; and an expanded Storm Prediction Center (SPC) Enhanced Risk over the same area.

Ten minutes later, Tornado Watch 497 (5% Hatched) is issued, essentially in same region as the Enhanced Risk.

By 4:00 pm, I decided to attempt to intercept a large discrete storm tracking east from east of Des Moines. Around 4:40 pm the storm cell became tornado warned (Radarscope capture above). I hurried south on Interstate 380/US Highway 218 to get south of the cell, but now the storm was becoming outflow and linear.

5:39 pm. Radarscope capture. I have now reached my spotting location at the Phillips 66 Truck Stop just off US Highway 218 at Ainsworth, Iowa in Washington County. The severe-warned storm has lost its tornado warning and now is linear and bowing out (northwest of my location).

5:44 pm. Bowing linear storm with severe warnings all up and down its length.

5:56 pm. Looking northwest at an approaching shelf cloud, in the more intense area of the storm, as seen from the Phillips 66 Truck Stop. 

5:59 pm. Shelf cloud panorama. The tornado threat has now diminished, with only QLCS (Quasi-Linear Convective System) spin-ups possible.

Radarscope capture corresponding to the panorama image above it.

5:59 pm. Looking north at shelf cloud in the more intense region of this severe-warned storm as it begins to overtake my location.

6:01 pm. Close-up of the leading edge of the approaching shelf cloud looking northwest, showing the turbulent "whale's mouth" feature behind it.

6:02 pm. Leading edge of the shelf cloud in the western sky. Whale's mouth at background right.

6:02 pm. Looking northeast. The leading edge of the storm continues to overtake this Ainsworth, Iowa location. High winds are kicking up dirt in the parking lot at center.

6:20 pm. Looking northeast at the truck stop. At this location, wind speeds never surpassed 60 mph, and no hail fell here, despite heavy rainfall. A single (EF0) tornado touchdown was reported north of here, southwest of the Iowa City airport. Nikon Z6ii camera.