:Product: 3-Day Forecast
:Issued: 2026 Apr 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 5 (NOAA Scale
G1).
The greatest expected 3 hr Kp for Apr 21-Apr 23 2026 is 4.00 (below NOAA
Scale levels).

NOAA Kp index breakdown Apr 21-Apr 23 2026

             Apr 21       Apr 22       Apr 23
00-03UT       3.33         2.67         1.67     
03-06UT       4.00         2.00         1.33     
06-09UT       3.00         2.33         1.33     
09-12UT       2.67         2.00         1.33     
12-15UT       2.33         2.00         1.33     
15-18UT       3.00         2.33         1.33     
18-21UT       2.67         2.00         1.67     
21-00UT       2.33         2.00         1.67     

Rationale: Active periods (below NOAA G-scale levels) of geomagnetic
activity are expected on 21 Apr, with a slight chance for a G1 (Minor)
geomagnetic storm as the CH HSS effects wane.  No geomagnetic storms are
expected on 22-23 Apr.

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 Apr 21-Apr 23 2026

              Apr 21  Apr 22  Apr 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 Apr 21-Apr 23 2026

              Apr 21        Apr 22        Apr 23
R1-R2            5%            5%            5%
R3 or greater    1%            1%            1%

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