We get winds from all directions here in iowa (major tornado alley) but I guess I could pick a side I see storms come from the
Outdoor hutches... you need an overhang to keep rain from blowing into the cages. Best if the back of the cages faced the prevailing winds with shelter on three sides. With an overhang and three sides blocking precipitation you shouldn't need to have anything in the front of the cages.
There is usually a most-common prevailing wind direction, and you'd want to put the backs of the hutches towards that. But if winds are frequently squirrely like they were where we lived in Anchorage, and would blow rain/snow in under an overhang, having a tarp with a weighted bottom edge (2x2 wrapped up in and stapled to bottom) to drop down during wind/rain storms worked pretty well. In the worst storms we also stapled the tarp along the sides to keep it from getting ripped off by the wind.
You will need a way for them to get totally out of the rain, some hutches have a "doghouse" section on one end that is a little 4 sided box with a hole in the connecting wall. In Iowa, I think you are maybe going to need a solid floor or insulation (straw) on that section in the winter.
I have moved away from any sort of solid-bottomed section in the cages, as they always seem to become a serious headache to clean during the winter. Even without straw, "urine glacier" is the term that best describes what happens when it's so cold that urine freezes almost instantly on a solid floor, and continues to build up as time goes on. Add straw and it's a total nightmare (urine bricks and mortar, anyone?), and then when it warms up enough to thaw - which it usually does here, several times each winter - it's a septic swamp.
We sometimes have tried putting in a cardboard or wooden box stuffed with straw that can be removed after the worst of the weather; our mini breeds (Mini Rex and Polish) sometimes use them, but the bigger rabbits mostly just play with them.
As
@eco2pia notes, rabbits need to be kept from getting wet, but as you've discovered, they don't always do it themselves. But we've found that as long as they are truly protected from wind/precipitation, rabbits are fine in wire-bottomed cages all through the Alaskan winter.
Having the cages inside some sort of a shed or lean-to is ideal (and makes it a lot more pleasant for us to spend time with them!), but when we had free-standing hutches, the best design was to enclose wire cages inside a roof and three solid sides that extended down past the wire cage bottom by about a foot, with an overhang and the tarp option described above, to drop down when wind was incoming. The other tactic we used was to set up the cages in a close U-shaped configuration with their open sides facing each other. They formed their own shelter, blocking the wind for each other, whichever direction it came from.
. I was thinking about a hidey hole with straw, I worry about them peeing in it though. 
