Thranes, horses and owls! Oh my! (Grefe)
I'm assuming that the squares on the map are 5' x 5' ("Whenever possible, use units of 5 feet for movement and position." -PH, p.130). Grefe's normal move is 30', in the snow it is 20'.
Empty handed, Grefe heads north at a flat-out run (20'x4=80'...