All-season tires really won't perform well in heavy snow or cold, icy conditions. At the very least, consider having snow tires or winter tires placed on the front wheels which do most of the steering, braking and accelerating of FWD vehicles.
For your area and conditions, I would recommend changing to winter tires for the season and re-installing the all-season tires in spring...store the old ones in a garage if possible. Some people mount tires on separate rims and store them to avoid tire-changing costs every season. Doing so also prolongs the lifetime of the tires so you get more years out of two sets rather than one marginal set.
All-season tires are just a compromise between the best of certain types and as you have found out, really don't perform well in harsh conditions. If anything, buy all-season tires which lie on the scale of rubber compounds and tread design closer to winter condition capabilities although tread wear will suffer and over time, the tread pattern and depth usually loses it's ability to expel snow.
"Winter tires are designed for snow, cold, slush and icy weather conditions. They are essentially specialized tires that are designed to be used in the winter season whereas all season tires are meant for used in most conditions.
Some myths to dispel: there are car owners out there who are under the impression that the all season tires of today are so good and can deliver the same performance as the winter tires, and that winter tires are only meant for cars moving in snow clad, mountainous parts of planet earth, these assumptions cannot be further from the truth.
In particular, winter tires are made of superior rubber compound that have better traction compared to all season tires, and are designed to do well in cold temperature conditions. Special tread compounds are used in winter tires to improve traction. For some winter tires, soft studs tread fibers bite like metal studs are used and yet these compounds do not harm the road. The rubber's flexibility is retained even when the temperature goes up to zero degrees. Having a more flexible (= rubbery / pliable) tread surface means having more control and traction. The winter tires have silica-based, micro pore compounds that is used to 'bite' through the water film and increases the traction in the ice and snow.
All season tires have a different compound in which they have a average compound that provide good traction and better delivery in a wide range of road conditions. However, when temperature reaches below forty-five degrees Fahrenheit, the traction decreases. This is the point where all-season tire compounds begin to lose traction because it begins to harden.
Tread Design Differences Modern winter tires are designed to have a tread that can maintain a more comfortable and quieter ride compare to their predecessors. Its circumferential grooves were made wider in order to efficiently drain water and expel snow at the same time.
In addition, the grooves on the winter tires are made to be about 25% - 35% deeper than that of normal tires and thus provide better grip. It has a groove shape and special lug that allows more snow to be packed into the thread and expelled as it rotates for deep snow traction. It also has a high density and sophisticated spine design that help cut through the water in order for the tread compound to make a better contact with the road. It even has a rounder casing design to add traction by cutting into the snow surface.
Read more at............
http://ezinearticles.com/?Winter-Tires-vs-All-Season-Tires&id=418513
http://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=116
http://www.ehow.com/about_6313046_weather-snow-vs_-season-tires.html