A Dash 9 heads a San Bernardino to Atlanta Z train up Cajon Pass early on their trip east, and probably one of the least likely places they'd encounter snow on the cross-country trip.
An Atlanta-bound Z train is pretty normal on Cajon Summit. Two Dash 9s in the lead is a bit less normal. Running on the second day of snow on the ground is pretty dang rare.
An Alliance bound Z train storms upgrade at Summit with a tattered Dash 9 leader.