3-Day Forecast

Issued: 2025 Dec 18 1230 UTC
Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center and processed by SpaceWeatherLive.com

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 Dec 18-Dec 20 2025 is 4 (.67NOAA scale G1).

NOAA Kp index breakdown

             Dec 18       Dec 19       Dec 20
00-03UT       4.33         3.00         2.67     
03-06UT       2.67         3.00         2.67     
06-09UT       3.67         2.67         2.33     
09-12UT       3.33         2.00         1.67     
12-15UT       4.67 (G1)    1.67         1.67     
15-18UT       2.00         1.33         1.33     
18-21UT       2.33         1.33         2.00     
21-00UT       3.00         2.67         2.00     

Rationale

G1 (Minor) geomagnetic storms are expected on 18 Dec due to persistent CH HSS influences.

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 Dec 18-Dec 20 2025

              Dec 18  Dec 19  Dec 20
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 Dec 18-Dec 20 2025

              Dec 18        Dec 19        Dec 20
R1-R2           15%           15%           15%
R3 or greater    1%            1%            1%

Rationale

There is a slight chance for R1-R2 (Minor-Moderate) radio blackouts through 20 Dec.