Appears to be a version of the AT3 optimized for winter use with more spies and biting edges.
http://us.coopertire.com/Tires/Light-Truck/Discoverer-A-TW.aspx
http://us.coopertire.com/Tires/Light-Truck/Discoverer-A-TW.aspx
Interesting. It does look like they siped an ATP and then gave it a "severe weather" rating.
I have Cooper Discoverer M+S tires on my 4runner now, they are great in the winter.
It is an all season winter focused tire. Designed to be run year round. I wish these were out last year so I could try a set on my wife's new durango. I put the cooper weathermaster wsc winter tires on in 265/60-18. They were great over the winter. I put the factory terrible michelin latitudes back on for summer. It's winter again so the coopers are back on and I may leave them on next summer as an experiment to see how long they last. I would rather run something like this new ATW for a bit of dirt and mud use in the spring summer and serious winter use. Too bad they are all LT sizes right now.