The impossible ski-track

Another photo from my recent winter promenade in the forests and fields around Tungelsta. I don't know how this happened, I tweeted the Swedish Meteorological and Hydrological Institute but haven't heard back from them. The ski track is now higher than the snow surrounding it. I guess it can happen if the temperature changes from cold to very cold, and then to much warmer in a short period of time. What I do know is that it is an imposible ski-track at the moment!