PORTLAND, Ore. (KOIN) — Weather whiplash will continue for western Oregon and Washington this week. Foggy mornings will remain as afternoon sunshine helps warm temperatures across the region.

The morning fog is caused by a meteorological event known as a temperature inversion. That’s when cold air sits near the surface. Above that layer of cold air is a layer of warmer air. This prevents the two temperature zones from mixing. Thus, fog develops in the lower layers of the atmosphere.

This all comes as air stagnation advisories remain over the Willamette Valley through Thursday. That’s due to the lack of air movement or mixing.

Temperatures will continue to sit near normal in the mid to upper 40s through the end of the week.

Weather conditions will become more interesting this weekend. Colder air and the return of wet weather makes a comeback Saturday and Sunday. That’s where snow elevations are expected to drop over the Cascades.