We have had Vowls (not sure on spelling) that have come from across the street into our backyard, is it possible that these bad spots are their trails? could that cause this?

Voles Torri? I don't know what effect they'd have.
Do you have a dog or dogs? Or do your neighbours? Where dogs pee it turns grass yellow and kills it.

Have you tried feeding your lawn? Perhaps it needs a bit of a pick-me-up after the dry spell. If the grass is actually dead in places you will have to re-seed it. I believe dead organic debris under the soil like tree roots can cause mushrooms.

Voles would leave burrows that would tend to suffer from drought more quickly than the surrounding grass. I would also double check to see if these spots get less water from the sprinkler than other spots, or are slightly higher than the surrounding lawn. Dogs are a possibility, too, as Beattie says. If this lawn is new to you, and the same spots consistently turn straw colored for no discernible reason, it might be a good idea to do a few foot deep test holes in these areas to see if they have big rocks or old tree stumps underground. What kind of grass do you have, and what is your soil and summer temps like? With that info, I could give you a better idea of how to water your grass.