:Product: 3-Day Forecast
:Issued: 2025 Sep 15 1230 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
#
A. NOAA Geomagnetic Activity Observation and Forecast

The greatest observed 3 hr Kp over the past 24 hours was 7 (NOAA Scale
G3).
The greatest expected 3 hr Kp for Sep 15-Sep 17 2025 is 6.67 (NOAA Scale
G3).

NOAA Kp index breakdown Sep 15-Sep 17 2025

             Sep 15       Sep 16       Sep 17
00-03UT       6.67 (G3)    3.67         2.67     
03-06UT       5.33 (G1)    3.67         3.00     
06-09UT       5.00 (G1)    2.67         2.67     
09-12UT       4.67 (G1)    2.00         2.00     
12-15UT       5.67 (G2)    1.67         2.00     
15-18UT       5.00 (G1)    1.00         1.67     
18-21UT       4.00         2.00         2.33     
21-00UT       3.67         3.00         2.67     

Rationale: Periods of G1/G2 (Minor-Moderate) geomagnetic storming are
expected through midday on 15 Sep due to negative polarity CH HSS
influences, in addition to possible influence from the 11 Sep CME if it
passes in close proximity to Earth.

B. NOAA 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.

Solar Radiation Storm Forecast for Sep 15-Sep 17 2025

              Sep 15  Sep 16  Sep 17
S1 or greater    1%      1%      1%

Rationale: No S1 (Minor) or greater solar radiation storms are expected.
No significant active region activity favorable for radiation storm
production is forecast.

C. NOAA Radio Blackout Activity and Forecast

No radio blackouts were observed over the past 24 hours.

Radio Blackout Forecast for Sep 15-Sep 17 2025

              Sep 15        Sep 16        Sep 17
R1-R2           30%           30%           30%
R3 or greater    5%            5%            5%

Rationale: There is a chance for isolated R1-R2 (Minor-Moderate) radio
blackouts through 17 Sep.