Solar wind parameters are currently trending toward nominal levels following the waning influence of a positive-polarity coronal hole high-speed stream (HSS). However, conditions are expected to become disturbed again from December 3 as multiple solar wind structures interact with Earth’s magnetosphere.
According to the U.S. National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC), three distinct drivers will influence the solar wind during this period: a sector boundary crossing from positive to negative polarity, a co-rotating interaction region (CIR) ahead of a negative-polarity coronal hole high-speed stream, and a glancing impact from the coronal mass ejection (CME) associated with the X1.9 flare at 02:49 UTC on December 1.
The CME, first visible in SOHO/LASCO C2 coronagraph imagery at 02:48 UTC, has an estimated speed of approximately 1 000 km/s.
Modeling indicates the bulk of the ejecta will pass north and east of the Earth–Sun line, but its flank may compress the magnetosphere enough to produce G2 – Moderate geomagnetic storming.
SWPC forecasts unsettled to active geomagnetic field levels on December 2, increasing to G2 – Moderate conditions on December 3-4. If the CME and CIR arrive simultaneously, short periods of G3 – Strong activity are possible, though confidence in this timing remains low. G2 Watches have been issued for both December 3 and 4.
Under clear-sky conditions, auroral activity may be visible at geomagnetic latitudes down to approximately 55°, potentially reaching regions such as the northern United States from Washington to Michigan, southern Canada, and northern and central Europe (Scotland, Denmark, southern Sweden, northern Germany, Poland). It may also reach the South Island of New Zealand. Visibility will depend on local darkness and geomagnetic response at the time of impact.
The most intense phase of the disturbance is expected to occur during the night of December 3 into early December 4, depending on the CME’s arrival and the orientation of the interplanetary magnetic field (IMF). If Bz turns strongly southward, auroral visibility may extend further toward mid-latitudes.
A G2 – Moderate geomagnetic storm can cause temporary voltage fluctuations in high-latitude power systems, minor impacts on satellite operations, and occasional HF radio signal degradation at polar routes.
At present, solar wind speeds have decreased to around 415 km/s (258 miles/s), with the interplanetary magnetic field magnitude near 5 nT and a Bz component fluctuating between +/−4 nT. The values are expected to rise as the incoming structures reach Earth.