Most signs of spring are the welcome kind, including buds, blooms, warmer temps, and green grass. But gray-colored circles on your lawn? Not so much. Snow mold is caused by cold-weather fungi that primarily affect cool-season grasses. Signs of a problem aren’t noticeable until the spring when the snow melts.

https://www.scotts.com/en-us/library/lawn-disease-control/snow-mold-what-it-how-treat-it