Routine Space Environment Product (Daily)
Issued by NWS
Issued by NWS
411
FXXX10 KWNP 180031
DAYTDF
:Product: 3-Day Forecast
:Issued: 2026 May 18 0030 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 3.67 4.33 2.33
03-06UT 3.33 5.33 (G1) 2.33
06-09UT 3.00 3.67 2.00
09-12UT 2.33 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: Isolated periods of G1 (Minor) geomagnetic storms are
possible on 18-19 May due to a potential glancing blow from a 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
Radio blackouts reaching the R1 levels were observed over the past 24
hours. The largest was at May 17 2026 0339 UTC.
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 is a chance for R1-R2 (Minor-Moderate) radio blackouts
through 20 May, with no little to no R3 (Strong) blackouts expected.