Routine Space Environment Product (Daily)
Issued by NWS
Issued by NWS
735
FXXX10 KWNP 171231
DAYTDF
:Product: 3-Day Forecast
:Issued: 2026 May 17 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 5 (NOAA Scale
G1).
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 2.00 3.67 4.33
03-06UT 2.33 3.33 3.67
06-09UT 2.00 3.00 3.00
09-12UT 2.33 2.67 2.00
12-15UT 4.67 (G1) 2.67 1.67
15-18UT 2.33 5.00 (G1) 2.00
18-21UT 3.67 3.33 3.00
21-00UT 2.00 3.33 3.33
Rationale: G1 (Minor) conditions are likely on 17 May due to coronal
hole influence and on 18 May due to anticipated effects of a passing
CME.
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: A chance for R1-R2 (Minor-Moderate) radio blackouts remains
over 17-19 May due to the flare potential of multiple active regions on
the Suns visible disk.