:Product: 3-Day Forecast
:Issued: 2026 May 15 1230 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 15-May 17 2026 is 5.67 (NOAA Scale
G2).

NOAA Kp index breakdown May 15-May 17 2026

             May 15       May 16       May 17
00-03UT       2.33         4.33         3.00     
03-06UT       1.67         5.00 (G1)    4.67 (G1)
06-09UT       3.00         3.67         3.33     
09-12UT       3.33         3.33         3.00     
12-15UT       3.67         3.33         3.00     
15-18UT       4.33         3.33         3.67     
18-21UT       5.00 (G1)    3.33         3.33     
21-00UT       5.67 (G2)    3.33         2.67     

Rationale: G1-G2 (Minor-Moderate) geomagnetic storms are likely on 15
May due to the CIR associated with a positive polarity CH HSS. G1
(Minor) storming levels are likely on 16-17 May due to the CH HSS
persistence.

B. NOAA Solar Radiation Activity Observation and Forecast

Solar radiation, as observed by NOAA GOES-19 over the past 24 hours, was
below S-scale storm level thresholds.

Solar Radiation Storm Forecast for May 15-May 17 2026

              May 15  May 16  May 17
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

No radio blackouts were observed over the past 24 hours.

Radio Blackout Forecast for May 15-May 17 2026

              May 15        May 16        May 17
R1-R2           40%           30%           25%
R3 or greater    5%            5%            5%

Rationale: There is a chance for R1-R2 (Minor-Moderate) radio blackouts
through 17 May due to the flare potential of the regions on disk.