Smoke is colloidal suspension of particles dispersed in a gas, a.k.a an aerosol. Heat from the fires creates violent updrafts carrying the particulate remnants of former trees, grass and sage brush to significant heights. When big fires are nearby, it’s not uncommon to have bits of ash falling from the sky. Like any rising column of air, with some moisture present, cooling may condense water vapor to form a cloud as well. I would not willingly fly IMC into a smoke cloud from an active nearby fire. As smoke cools and disperses and mixes with atmospheric air masses its wilder nature blends in with regular air.
By the time smoke from a fire in Oregon or California hits Idaho, the temperature has equilibrated to be less dangerous to airmen, but retains its nuisance in the form of reduced air quality and visibility.