Fall seems to be progressing at a typical pace in the eastern Sierra. You can find links to various fall color reports in Dan Mitchell’s blog.
Autumn of 2007 was exceptional. The dogwoods around the 5000 to 6000 foot elevation in Yosemite were unusually red, as you can see in the photo above, made along Highway 120 west of Crane Flat in October of 2007. A week after making that image I met a ranger on my way down to the Tuolumne Grove and asked her about the color. She said that conditions were perfect, since we had had a warm September followed by a cool October.
We’ve had a warm September this year, but yesterday the temperatures dropped off a cliff. Monday’s high in Yosemite Valley was 87, Tuesday’s 65. Thursday and Friday are supposed to be slightly warmer, but then the weather is expected to cool off again. Could we have another great fall?
I’ve tried to find information that would back up the ranger’s claim that a warm September followed by a cool October brings good fall color. A Wikipedia entry discusses the anthocyanins that produce reds and purples, and says that “when the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop,” but nothing about the effect of warm temperatures followed by cooler weather. If anyone can point to better sources of information about this topic, please let me know! Otherwise we’ll just have to wait and see.