I highly recommend four snow tires. I purchased four 205/50/16 Michelin x-ice xi2
last fall, and mounted them on the stock ST rims. They replaced, for winter, the 17" Continental Contact DWS all season tires I used the prior winter. What a huge improvement in every regard! Snow traction, ice traction, braking, wet and dry traction and braking as well.
The Michelins are not inexpensive, but, what is your insurance deductible, and what is your peace of mind worth, when your spouse is out in a snow/ice storm??
Matt @ TireRack.com can help you find the best tires for you. But do get them. Good luck.