roduct: 3-Day Forecast
:Issued: 2026 Sep 15 0030 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 4 (below NOAA
Scale levels).
The greatest expected 3 hr Kp for Sep 15-Sep 17 2026 is 4.67 (NOAA Scale
G1).

NOAA Kp index breakdown Sep 15-Sep 17 2026

             Sep 15       Sep 16       Sep 17
00-03UT       3.33         3.67         3.67     
03-06UT       4.67 (G1)    3.33         3.00     
06-09UT       3.33         3.00         2.00     
09-12UT       3.67         2.67         2.67     
12-15UT       3.00         3.00         2.67     
15-18UT       3.00         3.33         2.67     
18-21UT       3.00         3.67         2.00     
21-00UT       3.00         4.67 (G1)    2.67     

Rationale: G1 (Minor) geomagnetic storms are likely on 15-16 Sep due to
the CH HSS effects combined with CMEs glancing blow.

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 2026

              Sep 15  Sep 16  Sep 17
S1 or greater   20%     20%     20%

Rationale: There is a slight chance for S1 (Minor) solar radiation
storms on 15-17 Sep period.

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 2026

              Sep 15        Sep 16        Sep 17
R1-R2           10%           10%           10%
R3 or greater    1%            1%            1%

Rationale: There is a slight chance for R1-R2 (Minor-Moderate) radio
blackouts on 15-17 Sep period.


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