>After conducting an assessment of the 78-year-old structure earlier this month, the U.S. Army Corps of Engineers announced that it was raising the dam’s risk category from “moderate” to “high urgency.”
>https://www.latimes.com/local/lanow/la-me-ln-prado-dam-flood-risk-failure-20190516-story.html
I bet it was already in the "high-urgency" category for 10+ years, but they hold the info back until they're ready to create a FF. The story finally goes public shortly before the boom to give it plausible deniability.