That’s less than half the rainy days compared to western Oregon cities such as Salem, Portland, & Eugene. A typical summer day at Lake Simtustus averages 10-12 degrees warmer than Portland or Salem, that’s because cool ocean air doesn’t push east of the Cascades.
Yet overnight temperatures are COOLER than Portland or Salem in summer; perfect for cooling off your RV after a warm day on the water. You’ll find far more sunshine in the warm season east of the Cascades than in the populated western part of Oregon. Wet Pacific Ocean air dries out moving down the east slopes of the Cascade Range. By the time it makes it to Lake Simtustus there isn’t much moisture left.