Product: 3-Day Forecast - Issued: 2025 May 31 1535 UTC
Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center.

Geomagnetic Activity Observation and Forecast

The greatest observed 3 hr Kp over the past 24 hours was 4 (below NOAA Scale levels). The greatest expected 3 hr Kp for May 31-Jun 02 2025 is 4.67 (NOAA Scale G1).

Rationale: G1 (Minor) storm conditions are likely early on 01 Jun as CH HSS conditions persist. By as early as late on 01 Jun to early on 02 Jun, conditions are expected to increase rapidly with the arrival of the expected CME from 31 May. G3-G4 (Strong-Severe) conditions are likely, with a chance for G5 (Extreme) levels on 01-02 Jun.

Solar Radiation Activity Observation and Forecast

Solar radiation, as observed by NOAA GOES-18 over the past 24 hours, was below S-scale storm level thresholds.

Rationale: There exists a slight chance for S1 (Minor) or greater solar radiation storms over 31 May - 02 Jun, due primarily to recent activity from and future potential of Region 4100.

Radio Blackout Activity and Forecast

Radio blackouts reaching the R2 levels were observed over the past 24 hours. The largest was at May 31 2025 0005 UTC.

Rationale: R1-R2 (Minor-Moderate) radio blackouts are likely, with a slight chance for R3 (Strong), over 31 May - 02 Jun due to the flare potential from multiple complex regions on the Suns visible disk. ****AMD for increased geomagnetic activity forecast****