The Soviet/Russian air force had/has a longstanding practice of seeding clouds in the Moscow region in advance of major holidays, on the theory that a three-day bender in the sun is preferable to one in the rain. I was unaware that dry cement was used, but I imagine that it would be effective. Provided, of course, that you took it out of the bag first.
Being of a certain age, I was of course immediately reminded of this:
Here is a very informative Wikipedia entry which, while probably accurate, is ipso facto shrill and left-leaning. Must Kurt Vonnegut be mentioned in everything?! (Welcome Instapundit readers!) It makes perfect sense for the original experiments to take place in upstate New York, where conditions for this kind of thing are almost always ideal. However, I would not necessarily rush to take credit for making it snow in the Berkshires in November.