High pressure will slowly dissipate across the region come Monday. Clouds will increase into the afternoon but will start off mostly clear. The late afternoon and early evening may bring a pop up shower or thunderstorm in the higher terrain, specifically the Cascades. Any shower or thundershower development could then move into the Klamath Basin. However, the chances for this will be similar to Sunday afternoon so I am not expecting much, if any at all.
By Monday evening a longwave trough will begin nudging inland. This is going to drop temperatures considerably, to below seasonal norms. Tuesday & Wednesday will bring spotty showers to the viewing area. Most of the rainfall will be light in nature, but most areas should be seeing at least a drop of rain. By Thursday, the system will move north and clear the area.
Conditions begin improving from here on out, into the weekend with sunny skies and more seasonable temperatures.
Have a great week!