499
FXXX10 KWNP 161231
DAYTDF

:Product: 3-Day Forecast
:Issued: 2026 Sep 16 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 4 (below NOAA
Scale levels).
The greatest expected 3 hr Kp for Sep 16-Sep 18 2026 is 4.67 (NOAA Scale
G1).

NOAA Kp index breakdown Sep 16-Sep 18 2026

             Sep 16       Sep 17       Sep 18
00-03UT       3.67         4.00         3.67
03-06UT       3.00         4.67 (G1)    2.00
06-09UT       2.33         3.67         2.00
09-12UT       1.67         3.33         2.67
12-15UT       3.00         3.33         2.67
15-18UT       3.33         3.33         2.67
18-21UT       3.67         3.33         2.67
21-00UT       4.67 (G1)    3.33         3.00

Rationale: Active to G1 (Minor) geomagnetic storm conditions are
expected on 16 and 17 Sep due to combined negative polarity CH HSS and
CME influences. Unsettled to active levels are likely on 18 Sep as
enhancements wane.

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 16-Sep 18 2026

              Sep 16  Sep 17  Sep 18
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 16-Sep 18 2026

              Sep 16        Sep 17        Sep 18
R1-R2            5%            5%            5%
R3 or greater    1%            1%            1%

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