I had a lunchbox in the front in the past. (previous owner install).
I'll never run a lunchbox in the front again if I drive in snow. (And I currently live in Manitoba, Canada...so we get snow).
The main problem is the "unpredictableness" of the lunchbox locking or unlocking at very inconvenient times, and spinning you suddenly. Very suddenly. And the short wheelbase of Jeeps makes that even more pronounced.
Such a time that happened to me was when I was going 15-20km/hr (10mph-ish) on the highway...on black ice...and it just decided to slowly spin me around in a circle, across the other lane, and into the ditch. I had as much control as a curling rock gliding down the ice.
Now granted, that was an extreme situation (black ice). There was literally cars in the ditch all over the place.
When in the snow, it's a lot more controllable...but still risky - especially in turns. My fear was that it can suddenly spin me just a couple of feet at any time - and while 98% of the time I regain control, there's that 2% time (I'm making up stat numbers fyi) that the sudden 2 ft it spun me takes me to a very undesirable situation.
My advice, if you're on a paved road/city in snow and have a lunchbox locker up front - stay in 2 wheel drive.
I think it's "fine" to enage 4x4 if you're offroad, as you don't have to worry about oncoming vehicles, etc.
I also think it somewhat depends on your definition of "snow". I've never been to San Diego, but I don't imagine they consistently get a lot of snow. (Maybe just have to worry about higher up in the mountains?). In which case, you can probably "get away with it" if you don't press the accelerator in turns.
(Unless you have an auto-locker in the rear, like a Detroit - then I definitely would say no to a Detroit rear/lunchbox front in snow).
However, I did drive my Jeep for several years in the snow (5-6 months/yr) with a lunchbox up front, so it can be done.
I just don't do it anymore, now that I know better.
For Devils's Advocate:
I will also add that I do have a friend that loves his Aussie lockers front/rear, and drives them in winter.
He has also spun out twice (once last year that totalled his Jeep on the highway).
But he put the same diffs in his next Jeep.
I believe he spun out because of his autolocker up front.
He still firmly denies the autolocker had anything to do with it...