A fleece jacket is a great choice for Yosemite. Mine is a cheap Columbia. I wear it all the time and by that I mean almost every day. It has lasted at least 10 years, so I highly recommend the brand. You don't need a Patagonia or other fancy jacket. I've worn mine on several winter trips to Badger Pass (up above the Valley on the South side).

Get a fleece hat or balaclaca to wear if if gets cold and some lightweight gloves. Get decent socks. Summer could be a scorcher in Yosemite, so a hat and sunglasses for sure. Something like a Tilley (pricey) or even a ball cap will do.

Also, I highly recommend the Rough Guide to Yosemite, a great little guide book. about $10, plus Tom Harrison's map of Yosemite.

There is a lot online about the park on both the official NPS site and the commercial sites. I believe the official site has a temperature history on it. The NOAA site will give you forecasts.
http://forecast.weather.gov/MapClick.php...6000&zone=1