A coronal mass ejection (CME) produced by an M4.2 solar flare from Active Region 4317 at 22:39 UTC on December 28 is expected to cause a glancing impact on Earth’s magnetic field late on December 31 into early January 1, triggering a G1 – Minor geomagnetic storm at the beginning of the new year.
This is the highest level predicted through the three-day outlook.
Modeling of the CME propagation suggests that the plasma cloud associated with the M4.2 event will only partially intersect Earth’s orbit, producing an indirect or grazing encounter rather than a full impact.
Although the CME is not Earth-directed in its entirety, its flank is expected to merge with a negative-polarity coronal hole high-speed stream already moving through the inner heliosphere.
It is this interaction that may enhance geomagnetic activity to minor storm levels.
Potential impacts are expected primarily at geomagnetic latitudes poleward of 60°. Weak induced current fluctuations in power grids are possible, while minor effects on satellite operations may occur. Aurora may become visible across high-latitude regions, including parts of northern Michigan and Maine in the United States.
Solar activity remained at moderate levels on December 28–29. Region 4317 produced the aforementioned M4.2 flare and a secondary C8.9 flare, while Region 4325 generated M1.3 and M1.0 flares as it exhibited rapid growth and magnetic complexity.
Region 4321 showed signs of restructuring as it approached the west limb but remained relatively quiet. Other active regions were stable or in decay.
The solar wind during the past 24 hours reflected near-background conditions, with speeds between 450 and 500 km/s, total magnetic field strength of 3–8 nT, and Bz components fluctuating between +5 and −5 nT.
SWPC forecasts background conditions to continue through December 30, followed by enhanced parameters on December 31 as the coronal hole and CME influence reach Earth.
The greater than 2 MeV electron flux remains at high levels, while the greater than 10 MeV proton flux continues at background intensity.
No additional Earth-directed CMEs have been identified in coronagraph imagery from SOHO/LASCO and STEREO-A spacecraft.
References:
1 Forecast Discussion – SPWC – Issued at 12:30 UTC on December 29, 2025