Yakima Public Works crews said all the roads have already been salted and deiced. They're on call 24 hours a day. If the snow starts to accumulate they'll start plowing the streets.
Also, about ten DOT rigs are out from Selah to the Lower Valley. They'll be on all the major highways. Crews will apply a sand and salt mix as needed.
It's a good idea to avoid driving unless you absolutely have to. Snow and ice can easily build up in these freezing temperatures.