That is likely natural fluctuations in demand. The grid operator has not announced any load shedding (they have not even announced any imminent need to shed load) and there's still another 5GW of available capacity according to the dashboard.
It doesn't seem very likely that the actual behavior of a large-scale stochastic system and the hour-ahead forecast of that system would part ways to the extent we're seeing, just by coincidence. If it wasn't an intentional curtailment of demand, perhaps there is simply an outage somewhere?
Maybe there was unintentional curtailment of some sort, idk. There's still no announcement of stage 3 emergency (intentional curtailment).
I am going to try to use "unintentional curtailment" in a future post-mortem report.
California declared a Stage 2 Emergency at 15:30 PDT today which begins curtailment of interruptible loads, a less drastic form of load shedding. A Stage 3 Emergency begins to affect firm load using rotating outages.
Yes, when I wrote that the Stage 2 Emergency had not yet been announced.
We're just in the last few minutes getting the stage 2 warning that capacity limits could be reached soon.