No, not snow. It’s the ‘cotton’ from the cottonwood trees, accumulating in the grass at DeKorte Park.  The Eastern Cottonwoods (Populus deltoides) are shedding their seeds in dense fluffy masses that are scattered by the wind. Each tiny seed has a tuft of silky white hairs which carry it aloft in search of fertile ground. In late spring, millions of cottonwood seeds fill the air around the meadowlands.

Many plants use the wind to disperse their seeds. Adaptations include gliders, spinners, parachutes, flutterers, and more. In the meadowlands, many common plants spread this way, since there are fewer mammals to transport seed (whether stuck to their fur or in their droppings) and fewer perching places for birds who might carry seeds to distant places.

Read a good seed dispersal article on Wikipedia here.

A variety of other wind-borne seeds. Images, including moving GIF, from: http://waynesword.palomar.edu/plfeb99.htm#cottony