FXXX10 KWNP 181231
DAYTDF

:Product: 3-Day Forecast
:Issued: 2026 May 18 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 May 18-May 20 2026 is 5.33 (NOAA Scale
G1).

NOAA Kp index breakdown May 18-May 20 2026

             May 18       May 19       May 20
00-03UT       2.33         4.33         2.33     
03-06UT       2.33         5.33 (G1)    2.33     
06-09UT       2.33         3.67         2.00     
09-12UT       2.00         2.67         2.00     
12-15UT       2.00         2.00         2.00     
15-18UT       5.00 (G1)    2.00         2.00     
18-21UT       4.00         3.00         2.00     
21-00UT       3.33         3.33         2.00     

Rationale: G1 (Minor) or greater geomagnetic storms are are possible on
18-19 due to potential interaction with the periphery of a passing CME
that left the Sun on 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 18-May 20 2026

              May 18  May 19  May 20
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

No radio blackouts were observed over the past 24 hours.

Radio Blackout Forecast for May 18-May 20 2026

              May 18        May 19        May 20
R1-R2           40%           45%           45%
R3 or greater    5%            5%            5%

Rationale: There exists a chance for R1-R2 (Minor-Moderate) radio
blackouts over 18-20 May.