Wow - great story! You convey the feeling very well.
Saw one of those in Minneapolis back in the early '80's. Right in the city.
As you say, the wind stopped - then it poured such a heavy rain - I've never
seen rain like that. The funnel went through several miles from where I was. I
remember an MTC bus ended up in an auto parts store - Inside the display
window - almost looked like they were selling it.

I'm amazed you're having 85 degree evenings in Iowa City in mid April.
Is this typical?