Sac Spider, or maybe Ghost Spider
We were spotting these smallish (less than a quarter-inch long), pale spiders off and on all through the winter of 2013. This particular one was found on an exterior door on a part that was covered by a snowbank on March 2, 2013. It was evidently running around under the snow.
There was also at least one living in our car for most of April, and as the snow started melting we saw them regularly cruising around on our house siding whenever the temperature got above freezing. They evidently are roving hunters, not web-weavers. They were pretty willing to tackle whatever they could, too. While I can’t be absolutely sure it was the same species, I think it was one of these that I saw fly past riding on the back of a midge about twice its size. The pair of them ran into the side of our house, at which point the spider then quickly dragged the midge into a crack in the siding, presumably to finish it off.
I thought they were wolf spiders at first, but the eye pattern isn’t quite right. Wolf spiders have two central eyes that are much bigger than the other eyes, with four eyes underneath and two more around on the sides. This one has all the eyes about the same size, with two central eyes and the other six all running in a close arc across the face.
It looks like it may actually be either a Sac Spider in the family Clubionidae, or possibly a “Ghost Spider” in the family Anyphaenidae. BugGuide gives the distinguishing features between these two families as “[ghost spiders] have two rows of club-shaped hairs on the bottoms of their feet, and their tracheal spiracle is located well in front of the spinnerets, unlike most spiders which have their tracheal opening right in front of the spinnerets.” I don’t think I can see either of these details in my pictures, so we may be out of luck here.
There’s a pretty good chance that this is an immature spider, too. A lot of spiders go through the winter immature, eating the sorts of tiny things that one can find in the leaf litter.
Sac spiders are known for building little silk hideouts, often in curled-up leaves, which they hang out in when not hunting. So if you find a plant with a curled leaf, unroll the leaf, and have a spider suddenly dash out and run up your arm, it may be one of these (although I’ve had the unrelated jumping spiders do the same sort of thing to me).