for those , who doesnt use snow tires I wanted to share my experience..
here , in my city as general most of the days of winter roads are either dry or wet.. rarely snowy..
but once snow falls down , except the main roads all secondary roads are snowy for some days, I use snow tires for both of my cars from november 15 to march 15 regardless of the road conditions.. This have two advantages, first your summer tires thread remains untouched for that period so you can use them longer , second you have better compound tires which work better in cold/wet/snowy roads..
Unless the temperature stays below 15-17 celcius you can use your snow tires normally..(road surface not important)
only condition you must obey is, dont go faster than 70 mph on a dry road.. (and please dont try sideways

)
In this style I use them minimum 4 sometimes 5 years..
and for hills, even the best type summer tires will fail on snow.. and dont forget, biggest problem is brakes..
ps: one point I forgot to say.. snow tires must be narrow not like summer tires.. 205 or say max 215 width is more than enough..so wont be expensive like summer tires.. and using them with seperate rims (second hand is ok) say 15-16 size will be also economical..