Yury,
September is my favorite time to hike. There is always a chance for a thunderstorm, but not as likely as July/August. I always carry a Marmot Precip rain jacket & pants. I use the jacket more for wind protection than rain in Sept. I can't recall the last time I used the rain pants in Sept.
The afternoons are usually warm to hot, the evenings are chilly after the sun goes down and the early mornings are cold (around freezing or below for a few hours). Be prepared for a wide range of temps in a 24 hr period. Layers, layers, layers.
The skeeters are minimal in Sept, although with the late snow melt this year, they may be around a little longer.
Wazzu
