What are these "snow tires" of which you speak? Do you mean you actually have special tires for driving in snow?
Heh-heh...I grew up in that nasty white stuff...I usually watched the weather pretty closely after mid-October, (grew up in Spokane, and have even seen snow on Halloweeen) and if the weatherman started hinting about snow, I'd get them on...I waited for studded tires until they were absolutely necessary however. (yes, I generally had 2 sets of snows for each rig...AND chains for them as well.
When we lived in Wyoming, usually just after Labor Day I put the snow tires on everything, because at 7500 feet, you just never know when you might get up to a white surprise...