Thanks for the comments. I hope others like yourself chime in. Although it's a bit anectdotal it sounds like you've kept some records..
Like you, I enjoy the fall. I chose this time of year to go to the sierras to get some more variety in the weather mix and to avoid the crowds. Work is also covering my airfare since I have business in Sacramento around then too. Last year I was on the CDT in Montana...same two weeks...we got a bit of snow and night time temps in the 20's. Very enjoyable.
Yes I've already started looking at the CDEC. It's a bit of a task to determine the stations that have long term temp records vs. the snotel stations that just have snow courses. I'm not as familiar with the geography of the Sierras so i thought I would see if anyone had personal experience. I did get a 7 year stretch of data from the Central Sierra Snow Lab at around 7000'. From 2002 -2008 avg min air temp there was 38F. Some recent research seems to indicate the sierras are getting a bit cooler and the central valley much warmer, possibly climate change exacerbated by changing land cover in the valley: http://cat.inist.fr/?aModele=afficheN&cpsidt=17578376
So it may be that a time series based on the last 10 years will be more representative of what to expect???
I'm also not quite sure what elevations I'll be sleeping at yet which will ahve a big influence on air temps as well as microclimates...most of the temp records seem to be at lower elevations.
Anyways I'll be digging around into the station data more in the coming weeks.
Anyone have links for places to look for short and semi long term weather reports...NOAA is always a mess to navigate and seems to vary region by region as to what they have and where it's kept. As I get closer to my trip I'll benefit from knowin g where to find the most recent forecasts.
Insulation wise I'll likely have a WM ultralite, bivy sac, thin evazote pad with a new thermarest neoair + a Montbell thermawrap parka for extra insulation. I'm thinking that should be enough. to take me into the high teens.