How you determine what is "Northern" and what is "Southern" ?
On a county map of California, there's a nice line through the state.
The one Between San Bernardino-Kern-San Luis and Inyo-Tulare-Kings-Monterey ?
Yes, although Kern is a little debatable. You could put it in NorCal if you wanted to keep the Central Valley together, although there definitely are crazy people who commute from Bakersfield to LA.
There are two possible definitions, one which divides the state exactly along that line and another that puts Kern, San Luis Obispo and Santa Barbara Counties in NorCal. The latter is slightly more geographically reasonable, keeping the coast and Central Valley communities together, and also making the two states more even in population, but the former looks better on a map.