If we’re still talking 1988 as an analog, the switch flipped as soon as the calendar turned. October was almost rainless, November had 25/30 days with rain at PDX (and two of the “dry days” recorded traces). DJF was dry however.
Oct/Nov/Dec 2000 were all cold and/or snowy in the S. Lakes region, it wasn't only December, tho obviously that was the grand finale' of the early winter of lore up this way. That was 2 yrs before I moved to Marshall so I experienced it in S. Bend IN which wasn't ground zero. For SWMI I believe Dec 2000 was the snowiest on record.
I actually see just enough westerly flow every few days to regularly wash out the lower atmosphere without appreciably altering the weather pattern. Might mean cleaner air with a few sunnier days thrown in there. Perfect early Fall weather before what I assume will be a warm and wet November.
Shadow ratios will keep everything cool and damp north of 46° which will help with fog and keep temps down. Then we have the inversion factor with sun angles ~36° which is near the sweet spot of ineffective heating and brightness.
Air quality is probably going to suck by the 21st.