Overview
- The cut‑off low dropped out of the Gulf of Alaska and moved into the region Wednesday night, producing steady rain through Thursday morning and concentrating the heaviest totals over San Francisco.
- Downtown San Francisco recorded about 0.58–0.60 inch of rain, parts of the North Bay saw up to roughly 0.75 inch, and the Sierra recorded fresh snow with Mammoth Mountain reporting about 3–5 inches.
- Forecasters say the system was unusually hard to predict because it was a cut‑off low that separated from the main jet stream, which led to precipitation totals that exceeded National Weather Service forecasts.
- The main practical effects were wet commutes and a small chance of isolated thunderstorms and lightning in parts of the East and South Bay, with the storm center pivoting south and most of the rain moving beyond Monterey by Thursday afternoon.
- The late‑season rain pushed San Francisco’s May totals above the long‑term average, marking a second wetter‑than‑normal month recently, and officials say the event is brief with a drying and warming trend expected Friday into the weekend.