[DonC]

Duane:
Sorry I'm so late chiming in but I've been out of touch for a bit.
September can be a little bit iffy. Usually the first half of the month is pretty good but the last half can be wet.
Two of the past 5 years the last half of the month has been quite wet while the first half was fine. The rest of the time the last half has been in and out.
Returning from longer trips I've managed to get in just before it rained for a week (well, one of them I got caught for the last 80 miles). Once you get south of the Ashland and the mountains and cross into CA it's usually pretty good.
I do Snakes to the Lake in late September with the Bay Area club and I've hit rain in Oregon one of the 3 times I've gone. Last year I drove the Cobra down and back on I5. Cold in the morning but T shirt weather in the afternoon. As I said, a bit of a crap shoot. Bring a trash can liner to use as a poncho just in case.
DonC