Overview
- NOAA’s Space Weather Prediction Center and the U.K. Met Office have issued geomagnetic storm watches for December 9, citing a full‑halo CME tied to a December 6 M8.1 flare with a credible chance of G3 conditions.
- The CME is forecast to arrive early to midday December 9 (UTC), with models projecting Kp values near 6–7 and the auroral oval expanding toward mid‑latitudes across northern U.S. states, Canada and parts of northern Europe.
- Actual visibility and storm strength depend on the CME’s magnetic orientation, with a sustained southward Bz favoring stronger auroras; forecasters stress several hours of arrival uncertainty.
- Potential effects during strong intervals include temporary GPS inaccuracies, HF radio issues, increased satellite drag and surface charging, and voltage irregularities in high‑latitude grids, which operators typically mitigate.
- Real‑time monitoring via SWPC updates and 30‑minute aurora forecasts is recommended, and recent flaring from Region 4299, including an X1.1 on December 8, could extend activity into December 10–11 if subsequent CMEs arrive.