In winter conditions, the difference between all-season tires and winter tires is HUGE. What many people don't realize is that they're not just for snow and ice; winter tires grip much better in frigid temperatures, even when the roads are dry
, thanks to their ability to remain soft and pliable at those temperatures. All-season tires are designed as a compromise - okay in warmer temperatures (not as grippy as summer tires, but okay), and okay in cold temperatures (not as grippy as winter tires, but okay). Winter tires do better at the specific conditions for which they were designed.
Note that there are three types of winter tires. Using the Tire Rack terminology: "studless ice and snow" winter tires, "performance" winter tires, and "studdable" winter tires. The "studless ice and snow" winter tires give the best grip on ice and snow, but their handling when temperatures aren't so cold can be only so-so and less responsive. The "performance" winter tires offer better handing on warmer days than the studless variety, but aren't quite as grippy on ice and snow. "Studdable" winter tires really aren't a good choice, because tests have shown that in most winter conditions, today's modern "studless" winter tires give better traction than the studdable tires with studs installed. (Ref 1
) (Ref 2
) The use of studded tires is also illegal in many of the states and provinces with some of the worst winter weather.
Whether you need winter tires, and which type you choose, may depend on the conditions you face. If you live in an area with mild winters, or if you have another vehicle you would use when winter strikes, all-seasons might be sufficient for your needs and you might not need winter tires at all. If you do a lot of long-distance interstate driving, the performance winter tire might be a good choice. If your winter driving is mostly on local streets that aren't always kept clear, the studless ice and snow tires might be best. If you have no alternative but to drive even in the worst winter weather - maybe you're an emergency responder, or maybe you just HAVE to drive to work - and you absolutely must get where you're going no matter what, then the studless ice and snow tires are probably a good choice. And if you live in a cold climate with a fair amount of snow and/or ice as well as frigid temperatures, again, the studless might be best.
If you want to use winter tires, it's worth it to get an extra set of wheels, so you only have to get the tires mounted and balanced on the wheels one time. If you don't already have an extra set of wheels, you can find a used set of stock wheels for as little as $200, on eBay or at car-parts.com as well as in the Classifieds forum here.
I've considered winter tires money well spent. As I see it, all they have to do is prevent an accident once, and they've paid for themselves (depending on the amount of your insurance deductible). And because I only use them for 2-3 months a year, they don't get many miles on them each year; I just buy them once, and that one set then lasts many years.
Last year I needed to buy a set of winter tires for my MDX. Because I live in an area with extreme cold temperatures (temps of -10F or colder are not uncommon) as well as plenty of snow, I wanted the studless ice and snow tires. On the advice of the knowledgeable folks at Tire Rack, I got the Bridgestone Blizzak DM-V1. I love 'em.
Of course, there's also the "jinx effect".
If you buy a set of winter tires, you will then have very mild winters. If you don't buy them and try to get by on all-seasons, you will then have very harsh winters. In which case, it's easier to get around on winter tires when you don't need them, than on all-seasons when you really need winter tires.