Subj : 3 Day Space Weather Forecast
To   : All
From : Sean Dennis
Date : Mon Sep 21 2026 12:19 am

:Product: 3-Day Forecast
:Issued: 2026 Sep 21 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 3 (below NOAA
Scale levels).
The greatest expected 3 hr Kp for Sep 21-Sep 23 2026 is 2.00 (below NOAA
Scale levels).

NOAA Kp index breakdown Sep 21-Sep 23 2026

             Sep 21       Sep 22       Sep 23
00-03UT       1.67         1.67         1.67     
03-06UT       2.00         2.00         2.00     
06-09UT       1.67         1.67         1.67     
09-12UT       1.33         1.33         1.33     
12-15UT       0.67         0.67         0.67     
15-18UT       1.33         0.67         0.67     
18-21UT       1.33         1.67         1.67     
21-00UT       1.67         1.67         1.67     

Rationale: No G1 (Minor) or greater geomagnetic storms are expected.  No
significant transient or recurrent solar wind features are forecast.

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 21-Sep 23 2026

              Sep 21  Sep 22  Sep 23
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 21-Sep 23 2026

              Sep 21        Sep 22        Sep 23
R1-R2            1%            1%            1%
R3 or greater    1%            1%            1%

Rationale: No R1 (Minor) or greater radio blackouts are expected.  No
significant active region flare activity is forecast.


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