Moderate M1.1 solar flare erupts at 02:39 UTC on October 18, 2025

A moderate M1.1 solar flare erupted at 02:39 UTC on October 18, 2025.

This flare began at 02:26 UTC, peaked at 02:39 UTC, and ended at 02:47 UTC, sourced from region 4246. Today’s flares include an M1.0 flare from region 4256 peaking at 00:40 UTC, a C2.9 flare from region 4246 peaking at 02:09 UTC, a C9.5 flare from region 4246 peaking at 02:24 UTC, and the M1.1 flare from region 4246 peaking at 02:39 UTC.

In 24 hours to 00:30 UTC on October 18, solar activity increased to high levels due to numerous M-class flares. Decay and growth were noted in several sunspot regions, and an active filament produced no observed ejecta. No Earth-directed coronal mass ejections have been reported.

Minor to moderate (R1–R2) radio blackouts are likely through October 18, with a slight chance for an isolated R3 (strong) event. Flare probabilities decrease slightly on October 19 and October 20 as region 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. 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 before returning to high levels on October 19 and October 20. There is a slight chance for a greater than 10 MeV proton event above the S1 – Minor level through October 18.

Over the past 24 hours, solar wind parameters were at nominal levels until 09:30 UTC on October 17, when an interplanetary magnetic field enhancement occurred, likely due to a glancing CME from October 13–15. The total field increased to 14 nT after 20:20 UTC. Solar wind speeds remained near 380 km/s. Possible enhancements are anticipated through October 18 due to glancing CME influences, followed by a transition into 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 with the possibility of continued activity into early October 19. Further unsettled to active conditions are likely as a negative polarity coronal hole high speed stream arrives on October 19.