(bounce) If nobody else does, I'll take a crack at it even though you're out of my comfort zone. Do you know what type of grass you have? When was it put in? What and when did you feed it?

The pattern looks almost fungus like to me. Is the grass all matted down and loose in the yellow parts? I had something similar a few years ago (see photo.) Treating with several rounds of fungicide and reseeding worked for me. It seems too early for fungus though, usually it’s when it’s warm and wet outside. Unless this happened last summer and the other grass is just greening up around it?

I was thinking it might be a lawn seeded with a tri-mix and one of the varieties got a disease leaving the rest untouched.

Also, what does snow mold look like?

Not usually like that and not usually this late. Gray snow mold--which we all get during snowy winters if we leave the grass too long or feed too late--tends to simply slow return growth the following year.

Pink snow mold can be fatal, but fortunately, it's rare, not patchy like that (it kills in larger patches, more like wide swatches, and actually looks pink on bare ground when the snow melts.

This looks more like a cultivar that died, inconsistent feeding, bad soil, bad watering, or overall poor care.