The biggest risk is from an unseasonal warm rainstorm. Sunshine warmth has a beneficial evaporative effect to the high elevation snowpack. Somewhere upthread there was information on the percentage of moisture evaporated in sublimation (solid to a gas).
The risk to the spillway right now is if the worst combination developed - a warm pineapple express. That would generate the greatest inflow spike.
AS for the norm, perhaps others have the typical history data (although this may not be exactly comparable to the existing snowpack).
Some Sierra snow pack is still substantial, but there's just not much left in the Oroville Reservoir catchment area. I'm not sure warm rains would cause much snow melt contribution any much to the reservoir inflow. It would be far worse in other Sierra watersheds further south.
Below is yesterday's 24-hour snow melt. Brighter Blue = 1.4" to 2" water equivalent from melt, green line is the Oroville Dam watershed boundary.
1"+ would normally have been a rather heavy melt day a copule of months ago with 70%+ snow cover across the whole watershed, but snow cover is only something like 3% today.
[Source: NOHRSC]
For comparison, here's what it looked like in March. This was for 72 hours, but you can see the snow cover was far greater.
