ARRL Solar Report June 4, 2026

Solar activity went from low to high this week. Activity was dominated by Region 4455, which produced frequent C-class flares alongside three significant flare events: an M9.3/Sf on June 1; as well as an M7.7/1b and an X1.0/1n on June 3.

There are eight numbered regions on the visible disk. Region 4455 remains complex, maintaining its anti-Hale configuration and displaying a newly developed delta structure. Continuous flux emergence and spot growth with penumbral development were observed just ahead of its mature, positive polarity lead spot. Regions 4458 and 4459 both showed growth and consolidation, with Region 4459 showing rapid spot development in its trailing area and gaining a mixed-polarity gamma configuration. Region 4461 also showed flux emergence driving a gamma configuration, though extreme foreshortening near the limb limits high-confidence analysis of its overall complexity. Region 4462 consolidated and showed increased separation between its poles. The remaining regions were stable or in decline.

Several eruptive events occurred during the reporting period. An M9.3/Sf flare June 1 was accompanied by wideband radio emissions, including a Type IV radio sweep with an estimated shock velocity of 253 km/s, and a 10.7-cm radio burst. An associated coronal mass ejection (CME) became visible in LASCO C2 imagery on June 2. While faint in coronagraph imagery, GOES/SUVI imagery implies a partial to full halo profile, and COR2 triangulation confirms an Earth-directed component. Modeling indicates this event is the most Earth-directed CME of the period’s events.

The M7.7/1B flare on June 3 was accompanied by wideband radio emissions, including a Type IV sweep, a Type II sweep with an estimated shock velocity of 313 km/s, and a prominent three-minute 10.7-cm radio burst. The associated CME was first seen in LASCO C2 on June 3. GOES/SUVI 304 imagery shows much of the ejecta was deflected significantly northward by an adjacent positive polarity coronal hole. STEREO COR2 imagery and modeling shows that, while it retains an Earth-directed glancing component, it is the least directly-targeted event of the period.

Solar activity is expected to be at moderate to high levels through June 6. M-class (R1-R2/minor-moderate) flaring remains likely, with a slight chance for X-class (R3/strong or greater) events, primarily due to the eruptive capabilities of Regions 4455, 4458, and 4459.

Solar wind parameters continued to be slightly elevated with conditions reflecting possible embedded transient influences. Wind speeds held steady near 400 km/s for most of the period before a distinct increase to near 450 km/s late in the period. The phi angle showed a distinct transition into the positive (away from the Sun) sector late in the period.

Mild enhancements are expected early on June 4 under the initial onset of positive polarity high-speed stream (+CH HSS) influences. Conditions will escalate dramatically mid-to-late on June 4 with the arrival of the multiple June 3 CMEs. These significant enhancements are expected to persist through June 5 with elevated conditions persisting through June 6.

The 10.7-centimeter flux: June 4, 139; June 5, 135; June 6, 144; June 7, 132, June 8, 147; June 9, 126; June 10, 150.

Predicted sunspot numbers: June 4, 102; June 5, 97; June 6, 109; June 7, 93; June 8, 113; June 9, 86; June 10, 117

For more information concerning radio propagation, visit the ARRL Technical Information Service, read A Quick Guide to HF Propagation Using Solar Indices, and check out the Propagation Page of Carl Luetzelschwab, K9LA.

For customizable propagation charts, visit the VOACAP Online for Ham Radio website.