[pps43]

Ok I'll bite. Let's back of the envelope the probability.

In the past 17 years I experienced 5 blackouts, so return period is about 1,241 days. Among the cities that were mentioned, San Francisco is the smallest, with population about 865,000. Let's look at all US cities with population above 500,000. There are 34 of those.

The probability of having simultaneous blackout in 3 of 34 cities during 1,241 days is 1-exp(-C(34,3)/1241^2)=0.4%, or about 2% for the same 17 year period.

The above calculation assumes independence, but in reality probability is much higher because independence assumption rarely holds in real life. For example, we already observed multiple large cities in the Northeast having simultaneous blackouts in 2003.