My dog used to get that-- It always went away after she sat awhile in the snow.
You may want to give him regular baths with cold water centered near his hiney area.
Even if you have to take him outside to spray that area with cold water.
An herbal parasite dewormer -- especially one from either Barefoot Herbalist or Humaworm can also help, becuase this might be indirectly caused by a minor type of parasite that a week or two of herbal dewormer in his food may control.
They say it's good to deworm (with an herbal dewormer) a house pet once or twice a year anyway, as they often get common parasites alot. The parasites won't kill them, but maintenance deworming keeps the animal in prime health, and alleviates alot of future symptoms we would often have to take them to the Veternarian for.