Oroville itself is at 900 feet altitude, but the Oroville watershed extends into the Sierra Nevadas, including alpine valleys at 5000 feet. The Sierras have record snowpack this year (150 inches in places, so I hear).
Oroville is both north and west of where you are. Significant rain shadowing occurs east of the Sierra. and I think the "5000ft high" watershed number for Oroville may be low.
Yep all true. There's probably not any snow below even _6,000 or 7,000ft_ in the Sierras right now because the last storm, which was warm/rainy, melted it. This is another reason why the next storm won't put as much water into the reservoir.
Approximate watershed is seen in the map at: https://en.wikipedia.org/wiki/Feather_River