650
FXXX10 KWNP 201231
DAYTDF

:Product: 3-Day Forecast
:Issued: 2025 Sep 20 1230 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC contact on the Web
# http://www.swpc.noaa.gov/wwire.html
#
#             3-Day Forecast
#
A. NOAA Geomagnetic Activity Observation and Forecast

The greatest observed 3 hr Kp over the past 24 hours was 2 (below NOAA
Scale levels).
The greatest expected 3 hr Kp for Sep 20-Sep 22 2025 is 4.67 (NOAA Scale
G1).

NOAA Kp index breakdown Sep 20-Sep 22 2025

             Sep 20       Sep 21       Sep 22
00-03UT       1.67         1.67         4.00
03-06UT       2.00         1.33         4.67 (G1)
06-09UT       2.00         1.33         4.33
09-12UT       1.33         2.33         3.67
12-15UT       1.33         3.00         3.67
15-18UT       1.67         3.33         3.33
18-21UT       2.00         4.00         3.00
21-00UT       2.00         4.33         3.00

Rationale: G1 (Minor) geomagnetic storming is likely on 22 Sep due to
negative polarity CH HSS effects.

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 20-Sep 22 2025

              Sep 20  Sep 21  Sep 22
S1 or greater    5%      5%      5%

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

Radio blackouts reaching the R1 levels were observed over the past 24
hours. The largest was at Sep 19 2025 2141 UTC.

Radio Blackout Forecast for Sep 20-Sep 22 2025

              Sep 20        Sep 21        Sep 22
R1-R2           35%           40%           40%
R3 or greater    5%            5%            5%

Rationale: A chance for R1-2 (Minor-Moderate) radioblackouts will
persist through 22 Sep while increasing somewhat due to returning
regions.