If you do not have winter tires buy them in early October at best or at the latest NOW !! If you wait for cold temperatures or even worse, the first snowfall, you will have trouble 1) finding tires and 2) will face HUGE wait times to get them installed. The best thing is to have them installed on steel rims and buy a hydralic jack (about $35 at Cdn Tire) and swap them yourself - takes 30 minutes for each changeover and saves you about $70 per swap (usually $15 a tire for switch and balancing), so in 2 years you will have paid off your steel rims. The later you can wait to swap, the longer the winter tires will last. As mentioned previously, warm temperatures seriously wear out the softer compound on winter tires. My all seasons can make do for a light snowfall so I usually try to wait until Dec 1 or a major snowfall is forecast before changing them.
Traction especially on sporty cars is light years different with snow tires. Cars with narrower tires perform better in snow because less tire is in contact with the slippery surface. That is why sporty cars with the wider profile tires slide around so much. Snows are essential for these types of cars. Spend a bit extra and buy "good" snows as there is significant traction difference in higher end tires - there is significant tecnology in the better tires from better and softer compunds to air holes in the rubber and/or things like walnut fragments that improve traction. All the soft compound in a winter tire is in the outer tread. Once a winter has worn down to a certain point, the remaining rubber compound is the same as an all season tire. Performance at this point will be slightly better than an all season due to the more aggressive tread design.
Incremental cost is negligible - look at it this way... if you drive 12 months with a tire that lasts 3 years, you need new tires in 3 years. You can drive on that same tire for 6 years if you drive on it for only for 6 summer months. The all season tire will generally give you 3 years of excellent traction and another 1 or 2 years of acceptable traction. So over a 5-6 year period you will have virtually no extra costs other than the rims. Once you go to snows, you will never go back.
BTW, on a side note, Nokia (yes the phone maker) did used to make winter tires. That was their first base business. They expanded into cell phones and decided to sell off their tire business. No longer able to use the "Nokia" name, the brand name was changed to "Nokian" by the new owners in order not to lose the good name already built up.
If anyone wants a demonstration, once the snow falls, meet me with your car with all seasons. We will drive at 60 km/h and slam on the brakes. I virtually guarantee that I will stop around 50 ft less than you will especially on ice.
Go with snows and enjoy the beauty of a great Canadian winter with less worry.