Maybe cranefly? The larvae will eat the grass and kill it in spots.

Do notice a lot of craneflys in the yard. How do I treat?

You need to dig up a spot and check if you acturally have cranefly larvae, the link discusses this. You do not treat unless there is above a certain number.

You may also have red thread --a fungus.
I never had it until I got sod one year.
But I am not sure it completely kills a whole patch, unless you have a only one kind of grass in your seed mixture. It does not attack all turfgrasses. My red thread just mixes in with the rest of the grass and makes it spotty appearing. It grows out of it somewhat with drier weather and fertilizing, and slowly the more resistant grasses are taking over.

Here is a link that might be useful: cranefly check

Could be a fungus called Snow Mold. Appears as dead spots in early spring, in areas that were highly fertilized and growing lushly in cool damp weather. It thrives under snow cover on lawns that were fertilized late in fall, hence the name, but I think all it really needs is continuously cool and damp and low light conditions, like we've had all winter and spring ...

Sunlight, and letting the lawn dry on top between waterings, and a bit less nitrogen, and warmer temps fix it up. Summer, in other words, if we ever get that.