G4 – Severe geomagnetic storm watch issued for June 2 following strong Earth-directed CME

A strong, long-duration M8.1 solar flare erupted from Active Region 4100 at 00:05 UTC on May 31, 2025. The flare produced a fast and significant coronal mass ejection (CME), confirmed to be Earth-directed by space weather models.

Forecasts indicate the CME will reach Earth late on June 1, with initial geomagnetic storm conditions expected to reach G3 – Strong levels and a high probability of G4 – Severe storming on June 2.

“Confidence in an Earth-arrival component to this CME is good,” SWPC forecasters said. “However, timing and intensity are more uncertain. These watches represent potential based on our best analyses. We will not know the true nature of this CME’s geomagnetic storm potential until the CME arrives at our solar wind observatories located 1 million miles from Earth.”

“Upon arrival at those spacecraft, we will know the magnetic strength and orientation, which are very important to determine the levels and duration of geomagnetic storm conditions that are expected to occur.”

Under G4 – Severe geomagnetic storm conditions, the area of impact is primarily poleward of 45 degrees Geomagnetic Latitude.

Potential impacts include widespread voltage control problems and the possibility of protective systems mistakenly tripping out key assets on power grids, intensified induced pipeline currents, and increased drag on low Earth orbit satellites.

Spacecraft may experience surface charging and tracking problems, while HF (high frequency) radio propagation could become sporadic or blacked out. GPS and satellite navigation systems may be degraded or inoperable for hours.

Aurora displays may be visible at latitudes as low as Alabama and northern California.

“A slower storm ahead might cause a slight traffic delay, but G4 – Severe levels are possible by June 2,” space weather physicist Dr. Tamitha Skov said.

“This means aurora may be visible deep into mid-latitudes. Considering we expect big flares to continue on Earth’s dayside over the next few days, this means both the dayside and nightside radio bands will remain noisy, with periodic disruptions. Amateur radio operators, GPS/GNSS users like precision farmers, and aircraft/UAV pilots should plan accordingly.”

Updates

20:29 UTC, May 31

SWPC forecasters now predict that geomagnetic storm conditions are likely to reach G4 – Severe levels on both June 1 and June 2, with a decrease to G2 – Moderate levels expected on June 3.

09:32 UTC, June 1

The CME impacted Earth earlier than expected — at 05:42 UTC. The geomagnetic field rapidly responded with G1 – Minor storm at 06:17 UTC, G2 – Moderate at 06:33 UTC, G3 – Strong at 07:21, and reached G4 – Severe at 08:04 UTC before temporarily subsiding to G1 at 09:29 UTC.