Overview
- Model ensembles in late October and early November signaled an unusually early weakening of the stratospheric polar vortex, with NASA forecasts showing sharp drops in high-altitude wind speeds.
- NOAA and other agencies say a record‑strong “super” El Niño is ongoing and expected to peak this winter, which tends to bring warmer-than-average conditions across much of the northern U.S. and wetter weather in the southern U.S.
- Operational forecasters currently view El Niño as the dominant influence for November, but they caution that a downward‑propagating sudden stratospheric warming (SSW) could still trigger short, sharp cold snaps and snow in parts of North America and Europe later in November or December.
- An SSW changes the stratospheric wind pattern and can make the jet stream ‘snake’ so Arctic air moves south, but forecasters can only reliably predict individual SSW events about a week ahead and it typically takes two to four weeks or more for stratospheric changes to affect surface weather.
- People should expect generally milder weather this month with a watch for late‑season cold pockets; agencies including NOAA and the Met Office will update guidance in the coming weeks as model signals evolve and surface impacts become clearer.