200
FXXX10 KWNP 181231
DAYTDF

:Product: 3-Day Forecast
:Issued: 2026 Sep 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 3 (below NOAA
Scale levels).
The greatest expected 3 hr Kp for Sep 18-Sep 20 2026 is 3.00 (below NOAA
Scale levels).

NOAA Kp index breakdown Sep 18-Sep 20 2026

             Sep 18       Sep 19       Sep 20
00-03UT       1.67         2.00         1.67
03-06UT       2.00         2.33         1.33
06-09UT       2.00         2.00         1.33
09-12UT       1.67         2.33         1.33
12-15UT       1.67         2.00         1.33
15-18UT       2.00         2.00         1.33
18-21UT       2.67         2.00         1.67
21-00UT       3.00         1.67         1.67

Rationale: Isolated unsettled periods are expected on 18 Sep due to
lingering negative polarity CH HSS influences, with a transition to
mostly quiet conditions on 19 Sep and quiet levels on 20 Sep as nominal
background solar wind returns.

B. NOAA Solar Radiation Activity Observation and Forecast

Solar radiation, as observed by NOAA GOES-18 over the past 24 hours, was
below S-scale storm level thresholds.

Solar Radiation Storm Forecast for Sep 18-Sep 20 2026

              Sep 18  Sep 19  Sep 20
S1 or greater    1%      1%      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 Sep 18-Sep 20 2026

              Sep 18        Sep 19        Sep 20
R1-R2            1%            1%            1%
R3 or greater    1%            1%            1%

Rationale: No R1 (Minor) or greater radio blackouts are expected.  No
significant active region flare activity is forecast.