As already mentioned - why bother with the carp when you'll be fishing in Washington during our best trout and salmon season? Fall fishing in WA is awesome.

But, if you are stuck on carp, green lake does have good numbers, and good sized fish, but you will have plenty of competion from other foreign fisherman (mainly Russian).

I was recently at Potholes reservour (sp?) and saw tons of big carp in the 'wasteways' and in the main lake. I think they may still allow bow fishing for carp in this area. Now that would be fun

As for weather, just think 'layers'. Fall can be very unpredictable. But I would expect some rain, some sun, and cool\crisp nights. The nice thing about WA is the diffenent climates you can experience within a few hours drive. You get the mild, but more often foggy or rainy coastal environment, then there's the alpine areas of the OP and Cascades, and on the east side of the mountains we get the extreme hot and cold weather.

Hope you enjoy your stay.