Here's a link to Weatherbase. It will show weather averages for many cities and towns within each state, by month, over several years. Its a free app, and you can choose degrees C or degrees F.
Coming from the southern hemisphere where summer is just starting, you'll be coming to the northern hemisphere where winter is just starting, especially in the northwest due to altitude above sea level. Many RV parks and campgrounds will be closed for the season, and there will be snow.
I'd suggest that you wait until your winter is starting down under and chase the good weather.
