I think the stuff in the air in May is cottonwood or quaking aspen. Milkweed happens in September, more or less, according to latitude and altitude. And it's the seeds you're probably thinking of. Damn I miss those. But milkweed doesn't flower until June, makes little pollen anyway, and the flowers attract ants, and the leaves attract monarch butterfly caterpillars, being toxic. Urgh.
floating stuff
But snow is snow. Think of it as you will.
Re: floating stuff
I just know that there are times of year when the plant "stuff" floats and swirls around rather thickly... And yesterday just reminded me of it. :)