Subj : 3 Day Space Weather Forecast
To   : All
From : Sean Dennis
Date : Sun May 17 2026 12:19 am

:Product: 3-Day Forecast
:Issued: 2026 May 17 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 6 (NOAA Scale
G2).
The greatest expected 3 hr Kp for May 17-May 19 2026 is 5.00 (NOAA Scale
G1).

NOAA Kp index breakdown May 17-May 19 2026

             May 17       May 18       May 19
00-03UT       3.33         3.67         4.33     
03-06UT       4.00         3.33         3.67     
06-09UT       4.67 (G1)    3.00         3.00     
09-12UT       2.33         2.67         2.00     
12-15UT       2.00         2.67         1.67     
15-18UT       2.33         5.00 (G1)    2.00     
18-21UT       3.00         3.33         3.00     
21-00UT       3.67         3.33         3.33     

Rationale: G1 (Minor) geomagnetic storms are expected on 17 May due to
the negative polarity CH HSS ongoing effects. G1 (Minor) storming levels
are likely on 18 May due to possible glancing blow of a CME from 16 May.

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 17-May 19 2026

              May 17  May 18  May 19
S1 or greater    5%      5%      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

Radio blackouts reaching the R1 levels were observed over the past 24
hours. The largest was at May 16 2026 1742 UTC.

Radio Blackout Forecast for May 17-May 19 2026

              May 17        May 18        May 19
R1-R2           40%           40%           40%
R3 or greater    5%            5%            5%

Rationale: R1-R2 (Minor-Moderate) radio blackouts are likely through 19
May due to the flare potential and evolution of the active regions on
the visible disk.


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