Stuck in the Snow

The storm raged through most of the night, wind howling as the snow piled up outside the cabin. After the incident with the ice mephits, the party is able to hunker down safely in the building for the remainder of the night. While there isn't a lot of wood, you are able to scrounge enough to keep the fire going until morning.
Stepping outside in the aftermath of the storm, you can see that over a foot of snow has blanketed the world. The river is showing signs of ice forming along the banks, though the force of the current has kept the stream open. Your boat is still tied to the dock, but riding low with all the snow in it, and threatened by the encroaching ice near the shore.
Should anyone decide to look around the building, or make an excursion up the hillside for more firewood, they will find many tracks coming down the mountain and circling around the edge of the cleared land next to the building. Survival DC15 to recognize the tracks as belonging to a pack of wolves, at least 6, with one noticeably larger than the others. It appears they lead back up the hill toward a line of trees higher on the ridge overlooking the way station. No one can recall hearing any howls during the night, but the wind from the storm covered any other noises. Perception DC20 to notice two sets of tracks leading upriver 100 feet back from the shore.
There are 5 wolves and a winter wolf that were shadowing the party during the night. They have sent two of the wolves upriver while the others withdrew. They will wait for the party to busy themselves with clearing their boat, then ambush them. When they do, the five will surround the party and close on them while the winter wolf holds back. They will try to attack when someone is isolated or separated from the others, and target them. The winter wolf will try to use its breath weapon on as many as it can at one time.