SAN FRANCISCO — The rapid growth of Omicron is prompting officials to warn that hospitals could easily become overwhelmed, potentially within weeks, as they deal with a combination of the newest variant of the coronavirus along with patients hit by a holiday wave of the Delta strain. California and the rest of the nation now face a formidable winter. According to the state’s COVID forecasting models, there are plausible scenarios in which a winter surge could hit hospitals worse than the summer Delta wave, which strained facilities across swaths of the state. The combination is “a perfect storm for overwhelming...