(Microdochium nivale or Fusarium patch)
Snow mold is a type of fungus and a turf disease that damages or kills grass after snow melts, typically in late winter. Its damage is usually concentrated in circles three to twelve inches in diameter, although yards may have many of these circles, sometimes to the point at which it becomes hard to differentiate between different circles. Wikipedia
Melting snow, warmer temperatures
Break up any snow piles and fluff with a rake.
Potassium deficiency, Poor Drainage