fra spaceweather:
CME IMPACT, SEVERE GEOMAGNETIC STORM: Arriving
earlier than expected, a CME hit Earth’s magnetic field on March 17th
at approximately 04:30 UT. At first, the impact sparked a relatively
mild G1-class (Kp=5) geomagnetic storm confined to the poles. Since
then, however, the storm has intensified to G4-class (Kp=8), ranking it
as the strongest geomagnetic storm of the current solar cycle.