It’s related to real time rainfall, but it’s also related to water releases upstream. I’m with TVA - we have a river system and there is a timing factor to releasing water upstream and when it arrives at the next dam down the river. For example (and this is purely hypothetical, since I don’t have raw numbers in front of me), if TVA releases 100,000 cubic feet from, say, Guntersville Dam, it will be maybe 3 or 4 hours before that increased flow reaches the next dam downstream.
So in this case, they may have released water hours ago and that water got to Oroville and has since backed off because that particular volume of release has terminated. The number will go up and down, but on average, will be higher through and after the rain period.
The maps I'm seeing aren't showing any .. are there any dams upstream of Oroville that would be affecting its reservoir level ?
(disclaimer: i'm in PA and unfamiliar with CA other than being glad i'm not out there ;-)