Moderate M1.5 solar flare erupts at 10:51 UTC on October 18, 2025

A moderate M1.5 solar flare erupted at 10:51 UTC on October 18, 2025.

Today’s flares include several M-class events from region 4246: an M1.0 at 00:40 UTC, an M1.1 at 02:39 UTC, an M1.2 at 06:39 UTC, and an M1.3 at 06:58 UTC. C-class flares ranging up to C9.9 were also observed from the same region. Region 4248 produced activity including a flare at 07:14 UTC.

In 24 hours to 00:30 UTC on October 18, solar activity increased to high levels due to numerous M-class flares. Region 4246 showed some intermediate spot decay as it neared the western limb. Region 4248 was mostly quiet with slight spot number decay. Region 4256 displayed minor penumbra growth, while region 4257 was newly numbered during the period.

There is a likelihood of minor to moderate (R1–R2) radio blackouts through October 18, with a slight chance for an isolated strong (R3) radio blackout event. Flare probabilities are expected to decrease slightly on October 19–20 as region 4246 moves off the visible disk.

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

In the last 24 hours, solar wind parameters remained nominal until around 09:30 UTC on October 17, when an increase occurred in the interplanetary magnetic field, possibly related to a previous CME. The magnetic field strength increased to 14 nT later in the period, while wind speed remained near 380 km/s. Enhancements to the solar wind are anticipated through October 18 due to glancing CME influences, with a transition to a negative polarity coronal hole high speed stream expected on October 19.

During the past day, 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 possible carryover into early October 19. A negative polarity coronal hole high speed stream is expected to cause further unsettled to active geomagnetic conditions on October 19.