Yeah this is always tricky for runners living in snowy mountains. For us it is always a late start to running season. I recommend doing these runs on a treadmill/stair master combo if possible. This can break up the boredom. Get some good pod casts :-). Even fine to make the workout a mix of out door running and these indoor machines.
I don’t think doing laps on 5.8 will be the best substitute.