"but snow cover is only something like 3% today."
So where did all of the snow cover go? Just 11 days ago the State was saying that they had a contingency plan to use the spillway one more time "If water from snowmelt in the Sierra Nevada fills the reservoir harder and faster than currently expected,"...(link below)
Use Spillway one more time If water from snowmelt fills reservoir harder and faster than currently expected - May 20 2017
If you look at the snow water density map it shows the Oroville Catchment Basin near empty (white circled area).
Have you been following this? Why has the snow essentially disappeared in the Oroville Catchment Basin yet is dense (30 inches of water equivalent) exactly south on the southern edge of the Basin for a great distance?
Seems odd, in comparison with the news story. What's up?
Noaa map of water equivalent in snowpack. Oroville catchment basin (white circle) is almost nil while 30+ inch levels up and to the southern edge of the basin.???
As far as DWR statement, I imagine that was just cautious wording from a PR (not a engineering) standpoint
just in case. They have access to all the best models and forecasts. By 20 May, they would have known the releases/snowmelt/remaining snow cover put them in pretty good shape, but why stick their neck out and actually say
"...No more releases..."? A sufficiently powerful Pineapple Express two weeks later (now) would leave them with egg on their face - again.
DWR made that statement on the 20th, but started ripping things up in a serious way last week. A release after that point would have been problematic - erosion, debris in river, etc. Not catastrophic, but bad. Still, their actions last week tell me they were sufficiently confident of the low risk that they proceeded despite their earlier statement. If they ended up being wrong today, they would have reminded us that they did anticipate one more release. Expectations management, I guess.
Regional differences and weather patterns are enough to explain why the Oroville Reservoir basin melted off before the rest of the Sierra this year. They might get blasted next winter while the south remains dry. I've only been watching the weather there closely this year, but there is nothing like a consistent pattern across the entire Sierra. It's patchy and precipitation is often in narrow swaths. Tahoe and the eastern ranges generally get a lot more snow than the northern or southern ranges.
The 30+ inches of snow-water equivalent mostly applied to the Sierra mountain tops in the Oroville Watershed. Most of the catchment area had far less than that and it melted off weeks ago. They had a lot of snow this year, but nothing like the Tahoe snowpack below.
Those little blue areas on the snowmelt forecast (mountain tops/north faces) still do have several feet of snow and probably over 30" of snow water equivalent, but just in a few square km area. I'm sure there's still a risk of localized flooding from heavy melt runoff under those peaks, but nothing that translates to much of an effect overall on the Feather River forks.
I'm not familiar with the summer weather patterns there to speak to the possibility of torrential rains or another Pineapple Express in the Oroville watershed, but I don't think summer rain has been much of a problem there - at least not to the extent that it would force another release from the dam.
Hydro plant releases should be enough for this summer. I expect them to work well into December as well - the Nov. 1 'deadline' is another managing expectations thing. It would be extraordinary if they ever had to spill in November.