S2 – Moderate Solar Radiation Storm Alert issued on November 11

An S2 – Moderate Solar Radiation Storm Alert was issued on November 11, 2025, after the 10 MeV proton integral flux surpassed the 100 pfu threshold at 12:32 UTC. This alert indicates a moderate solar radiation storm according to the NOAA Space Weather Scale.

Potential impacts from this event include increased radiation exposure for passengers and crew in high-latitude, high-altitude flights, though the increase is small. Spacecraft may experience infrequent single-event upsets, and there could be minor effects on polar high frequency (HF) radio communications, such as signal fades at lower frequencies.

The triggering event for this alert was an X5.1-class solar flare from active Region 4274, which peaked at 10:04 UTC on November 11, 2025. This flare caused elevated energetic particle fluxes that resulted in proton levels reaching S2 – Moderate thresholds.