The 6-10 feet is somewhat misleading. The top of Thunder Mt. probably does have something like an 8-foot base. Thunder services about half of Baldy's skiable terrain. The major runs, steep groomers Robin's and Skyline, and the skier-packed mogul runs between them, should have good spring conditions from mid-morning onwards, depending on temps. The off-piste gladed areas have been difficult from what I hear, as new snow has been very heavy, and is set up and irregular. These areas are great in decent powder or smooth corn, but I don't think you're likely to get either. Off-piste you will probably want to ski where it's been skier-packed.
The intermediate chair 4 faces directly south but still has close to full coverage. With that exposure in sunny SoCal weather the window of opportunity is short, usually about 10:00AM to noon, and it's mush after that.
The lower chair 1 has a sun (and probably rock) exposed canyon run under the lift and several long steep shots dropping into the canyon from the right as you're riding the chair up. These are likely to have the set-up and irregular stuff, heavier than up top. Look for skier-packed lines as you're riding the lift. Near the bottom of the lower lift there will be lots of rocks and it can be worth walking the last 100 feet or so to save your equipment.
If you've never seen Baldy, it's worth half a day of your time even if you're confined to the core area of Thunder Mt. Coverage is still good, but you should be comfortable with a variety of unpredictable snow conditions. If you ski Squaw/Alpine in late April/May you might feel right at home.