Having lived in SoCal my entire ski career I have these 2 web pages you may find useful:
http://22.214.171.124/~bestsnow/scalnet.htm Brief description of the areas, with links to detailed resort guides for Baldy and Snow Summit written a decade ago but still applicable.
http://126.96.36.199/~bestsnow/scalhist.htm Weekly snow conditions history since 1976
Someone who lived in Colorado isn't going to be too excited about SoCal skiing unless the grade on that chart is at least "B."
Lifetime 14% of my skiing is in Southern California but it's well under 10% for the past decade. If you want to ski a lot, don't put yourself in the position of dependence upon the SoCal locals to do it. The past 3 years have been poor, with 2013-14 being the second worst in my experience since 1976. During my "family years" I averaged 24 ski days per season, but only 5 of them in SoCal.
If you're an avid skier you should figure out how to get to Mammoth multiple weekends per season. Instruction/snow conditions for your kids should be better too.
Big Bear/Snow Summit has excellent management and world class snowmaking, but minimal challenging terrain. So it's good for early season warmup and probably lessons for your kids.
Snow Valley is quiet, lots of easy terrain, haven't been there personally since 1986. It could be be good for you and the kids on your own. I would not assume that an area like that would have quality instructors though.
Baldy is high risk, high reward, big mountain skiing when it's good. Don't take your kids there until they are at least strong intermediates.
I avoid Mountain High unless both East and West are open. At the top of East is a very nice beginner chair, good for you and your kids on your own. I would not do lessons there, as they are probably at the more congested West.
Mt. Waterman also has a good beginner chair up top, but no lessons. The 2 areas having beginner terrain on the upper mountain is a plus for snow conditions.
The used ski is not a bad idea. SoCal can be hard on skis.
(Seasonal Affective Disorder! ...It was 100 here today).
September often has our hottest weather. Average temperatures are the same as July, with August being maybe one degree warmer. The "offset seasons" are a fairly unique feature of California weather. May and June will be much cooler than you expect most of the time. This also contributes to my bias about when to ski. Do not miss Mammoth in April, and you will be impressed even by Memorial Day vs. A-Basin.
I'm not sure how long the OP has been here, but this has been the hottest SoCal summer in quite a while. And the warmest water for your surfing too.
I decided to look it up:
It's not my imagination there were a lot more hot years in the 80's and 90's than during the past 15 years. There is no question that 2014 will be the hottest year in L.A. since 1997.
Edited by Tony Crocker - 9/18/14 at 1:25pm