Subj : 3 Day Space Weather Forecast
To   : All
From : Sean Dennis
Date : Wed May 21 2025 00:19:02

:Product: 3-Day Forecast
:Issued: 2025 May 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 May 21-May 23 2025 is 4.00 (below NOAA
Scale levels).

NOAA Kp index breakdown May 21-May 23 2025

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

Rationale: No G1 (Minor) or greater geomagnetic storms are expected.
Unsettled to active levels are expected through 23 May due to persistent
CH HSS activity.

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 May 21-May 23 2025

              May 21  May 22  May 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 May 21-May 23 2025

              May 21        May 22        May 23
R1-R2           35%           35%           35%
R3 or greater    5%            5%            5%

Rationale: Solar flare activity is expected to remain low as most
regions on the disk are fairly simple in their magnetic complexities.
There remains a 35% chance for R1-R2 (Minor-Moderate) and a 5% chance
for R3 (Strong) activity through 23 May.



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