G1 (Minor) Geomagnetic Storm Warning Issued
published: Monday, December 21, 2015 08:45 UTC UTC
A shock was observed at the ACE satellite at 15:28 UTC on the 19th (10:28 AM EST). The shock is likely the first of the two halo CMEs observed lifting off the Sun on 16 Dec. A subsequent geomagnetic sudden impulse was observed at 16:17 UTC (14 nT at the Boulder magnetometer). A G1 (Minor) geomagnetic storm warning has been issued for the rest of the UTC day.