A coronal mass ejection (CME) from the June 30 solar flare reached Earth at around 12:00 UTC on July 3, followed by a later disturbance that may have marked the CME’s main driver or an additional CME from July 1. The result was a G3 – Strong geomagnetic storm early on July 4.
According to the SWPC forecasters, the disturbance is likely associated with the CME from the June 30 X1.1 solar flare that began at 20:34 UTC, peaked at 20:50 UTC, and ended at 21:00 UTC near N18W18 on the solar disk. The flare produced an R3 – Strong radio blackout and was accompanied by Type II and Type IV radio emissions.
A more substantial enhancement was observed just after 21:00 UTC on July 3. SWPC said this may have indicated the arrival of the main CME driver or an additional CME produced on July 1. Total interplanetary magnetic-field strength increased to 24 nT, while Bz, initially northward, later turned southward to -19 nT. Solar-wind speed increased from about 535 km/s to nearly 630 km/s.
Geomagnetic activity reached G2 – Moderate levels during the 00:00–03:00 UTC interval on July 4, with planetary Kp at 6.00. It then intensified to Kp 7.33, corresponding to G3 – Strong conditions, from 03:00 to 06:00 UTC. Conditions eased to Kp 5.67, or G2, from 06:00 to 09:00 UTC, while the preliminary planetary Kp estimate for 09:00–12:00 UTC was 4.67.
A G3 warning was issued at 05:01 UTC on July 4, valid through 12:00 UTC on July 5. The G3 peak exceeded SWPC’s routine forecast issued shortly after midnight, which had called for G1 conditions with a chance of G2 levels on July 4 from the June 30 CME.
At G3 – Strong geomagnetic storm levels, power operators may need to make voltage corrections, and some protection devices can generate false alarms. Satellite components may experience surface charging, while increased atmospheric drag can affect low-Earth-orbit spacecraft and require orientation adjustments. Intermittent problems with satellite navigation, low-frequency radio navigation, and HF radio communications are also possible. Aurora can extend well beyond the usual high-latitude regions during storms of this strength, although visibility still depends on local conditions.
Aurora sightings were reported in both hemispheres on July 4. Regional observer groups reported displays from more than 30 U.S. states, including California and New Mexico, and much of Canada. Additional reports came in from southern Tasmania, including Abels Bay, South Arm, and Port Sorell.
Further CME activity from July 1–2, combined with possible influence from coronal hole CH72, is expected to bring active to additional G1 conditions on July 5, with an isolated G2 period possible. Activity is expected to ease up on July 6 as these influences wane.
A separate slow CME was observed in LASCO C2 imagery at 18:24 UTC on July 3, after the interplanetary shock had already arrived at Earth. SWPC said analysis of a possible Earth-directed component from that later CME was still underway.
Solar activity intensified sharply in the days leading up to the storm. More than 30 M-class flares were recorded between June 29 and 11:12 UTC on July 4, in addition to the X1.1 flare produced by Active Region 4479 on June 30.
Activity began with an M1.4 flare from AR 4479 at 21:40 UTC on June 29, followed by M1.3 and M5.8 events from AR 4475 on June 30. Solar activity then accelerated on July 1, when 11 M-class flares were recorded. The strongest was an M8.5 flare from AR 4478 at 23:09 UTC, while AR 4479 produced several others, including M3.5 and M2.6 events.
Four M-class flares followed on July 2, led by an M4.2 flare from AR 4479 and an M2.8 event from AR 4480. July 3 produced four more M-class flares: an M1.4 from AR 4480, an M6.7 from AR 4479, and M6.3 and M1.5 flares from AR 4478.
By 11:12 UTC on July 4, AR 4479 had produced a further eight M-class flares, including M4.0, M3.7 and M3.2 events. An M2.0 flare from AR 4480 and an M1.2 flare from an unnumbered region beyond the east limb brought the total for the day to 10.
References:
1 Forecast Discussion – NOAA/SWPC – July 4, 2026