Minor C9.5 solar flare erupts at 02:24 UTC on October 18, 2025

A minor C9.5 solar flare erupted at 02:24 UTC on October 18, 2025.

Today’s flares include an M1.0 solar flare from region 4256, which began at 00:23 UTC, peaked at 00:40 UTC, and ended at 00:49 UTC.

In 24 hours to 00:30 UTC on October 18, solar activity increased to high levels, attributed to numerous M-class flares. Sunspot regions 4246, 4248, and 4256 showed varying degrees of spot decay and penumbra growth. An active filament was observed near region 4250, but no Earth-directed CMEs have been detected.

Minor to moderate (R1-R2) radio blackouts are likely through October 18, with a slight chance for an isolated R3 (strong) event due to the flare potential of regions 4246 and 4248. Probabilities decrease slightly on October 19–20 as AR 4246 rotates beyond the western limb.

Active sunspot regions presently observed on the Earth-facing solar disk include AR 4246 (N24W81 – Beta-Gamma-Delta), AR 4248 (N07W54 – Beta-Gamma), AR 4250 (N04W45 – Alpha), AR 4252 (S13E01 – Beta), AR 4254 (N11E33 – Alpha), AR 4255 (S08E26 – Beta), AR 4256 (S15E52 – Beta), and AR 4257 (S08E75 – Alpha).

Over the past 24 hours, the greater than 2 MeV electron flux reached high levels, with a maximum flux of 3 330 pfu observed at 17:00 UTC on October 17. The greater than 10 MeV proton flux remained at background levels. The greater than 2 MeV electron flux is expected to decrease to normal to moderate levels on October 18 due to glancing CME effects, returning to high levels on October 19–20. There is a slight chance for a greater than 10 MeV proton event above the S1 – Minor levels through October 18.

Solar wind parameters were at nominal levels until 09:30 UTC on October 17, when total field and southward Bz increased, likely from glancing CME effects from October 13–15. Further increases in total field were observed after 20:20 UTC on October 17, with speeds near 380 km/s. Possible enhancements are anticipated through October 18 due to glancing CME influences, followed by a transition to a negative polarity coronal hole high-speed stream on October 19.

Geomagnetic field activity was at quiet to unsettled levels. Unsettled to active geomagnetic activity, with a chance for G1 – Minor storming, is expected on October 18 as glancing CME effects may continue into early October 19. A transition to a negative polarity coronal hole high-speed stream is expected on October 19, bringing further unsettled to active conditions.