The Sacramento Century route is pretty flat. Less than 1000 feet of elevation over 100 miles.
https://ridewithgps.com/routes/31149377
None of the elevation is an actual hill. The route sort of meanders between sea level at 40 feet ASL and you've got a nice midway point via Walnut Grove. South River Road is not the most bike friendly road in the area but it's got a decent shoulder and lots of visibility. So you won't have vehicles jumping up on you (or you them). Weather up here is mid 50s for the lows and mid 80s for the high. Winds in Sacramento are interesting, I've ridden a rectangle loop in the area and I've had a headwind the entire time. I would say prevails winds are out of the north and west.