Even though UA considers this to be a weather related delay, I would think better wording would make this clearer for 90% of travelers. Something to the effect of "Residual effects of prior weather."

Back in 2012, I was flying a UX flight BNA-ORD. The flight was 2+ hours late due to weather. The GA told us it was weather in Denver after he was asked several times how there could be a weather delay when it was sunny 72º. I got talking to the FA who said it wasn't in Denver, but due to arriving into SFO 5+ hours late the previous evening because of weather in BZE where they departed from.