
A G1 (Minor) geomagnetic storm warning was issued on 14 December at 1724 UTC (1224 ET) and remains valid until 15 December at 0400 UTC (14 Dec, 2300 ET). In relation to this warning, a G1 Watch was issued for 15 December. A co-rotating interaction region ahead of an expected negative polarity coronal hole high speed stream (CH HSS), arrived early and led to a disturbance in the Interplanetary Magnetic Field (IMF) strength and increasing solar wind speeds due to the CH HSS. Isolated periods of southward orientated Bz component has led to increased geomagnetic responses; including the G1 levels reached at 1759 UTC (1229 ET) and again at 2201 UTC (1701 ET). Any subsequent occasions of prolonged southward Bz component is expected to result in periods of G1 storming through the warning period. Since the CH HSS is expected to impact Earth's geomagnetic field for approximately 24 hours (through 15 Dec), the G1 Watch for 16 December has been dropped.