When do the ski trails get groomed?

Trails are groomed on a fairly regular basis especially after snowfall, heavy traffic, or freeze/thaw cycles. Grooming is almost always done overnight between 6pm and 6am. This gives the trails enough time to set up before skiers get out to the park. 

There are lots of factors that groomers need to take into account before they groom including snow temperature, snow saturation levels, and the timing of any snowfall.