I suggest using SDC to take the 6 am SMF-SFO on the day of departure, regardless of the weather. Myself, I always book the 6 am from LAX on transpac trips via SFO, because I have no faith that any flight after 6:01 am (exaggeration) wouldn't be delayed.
If the weather forecast for SFO will be bad for your date of travel, you should consider SDC the SMF-SFO segment to leave a day earlier. You can have up to a 24-hour connection in SFO, so ostensibly you have the entire day before to leave SMF.