Solar wind and the magnetic field
the first line of warningIF solar wind speed climbs past about 500 km/s and the interplanetary magnetic field turns south, THEN a geomagnetic storm is likely within hours, and it's time to protect the grid.
- Precedent → NOAA and NASA satellites at the L1 point already watch this, continuously, in public dataKnownThis is the single most mature warning on the whole page, and it's free to plug into. Ties directly to the Carrington card and the space weather page.