Space Weather for Radio
What the sun and the earth's magnetic field are doing now, from NOAA's Space Weather Prediction Center: it decides how well the HF bands carry. Updated every few minutes.
Right Now
Solar Flux (10.7 cm)
121
Above 100 helps the higher bands
Planetary K Index
3.33
Quiet
X-Ray Flux (flare class)
B9.6
M and X flares cause radio blackouts
NOAA Space Weather Scales
| Kind | Level | Now |
|---|---|---|
| Radio Blackouts | R0 | none |
| Solar Radiation Storms | S0 | none |
| Geomagnetic Storms | G0 | none |
The scales run from 0 (none) to 5 (extreme). R is the one that blacks out HF on the sunlit side, G is the one that sets the K index, S matters for polar paths and satellites.
K Index, Last Three Days
1.67
18-21
10-18
10-18
0.33
21-00
10-18
10-18
0.33
00-03
10-19
10-19
0.33
03-06
10-19
10-19
0.33
06-09
10-19
10-19
1
09-12
10-19
10-19
0.33
12-15
10-19
10-19
0.33
15-18
10-19
10-19
0.67
18-21
10-19
10-19
0.67
21-00
10-19
10-19
1
00-03
10-20
10-20
1
03-06
10-20
10-20
1
06-09
10-20
10-20
2
09-12
10-20
10-20
2
12-15
10-20
10-20
2.67
15-18
10-20
10-20
2.67
18-21
10-20
10-20
3
21-00
10-20
10-20
3.67
00-03
10-21
10-21
4
03-06
10-21
10-21
2
06-09
10-21
10-21
2.33
09-12
10-21
10-21
1.67
12-15
10-21
10-21
3.33
15-18
10-21
10-21
Each bar is three hours; the number is the K index for that period. Under each bar: the time range and date in UTC, then your own time. Oldest on the left. Green is quiet (below 3), yellow active (3), orange unsettled (4), red a storm (5 or more).
HF Band Guide (Rough)
| Bands | Daytime | Nighttime |
|---|---|---|
| 80 m and 40 m | Fair | Good |
| 30 m and 20 m | Good | Fair |
| 17 m and 15 m | Good | Poor |
| 12 m and 10 m | Fair | Poor |
A rule of thumb worked out from the solar flux and the K index above, lowered when the K index is high. It is not a forecast: the season, the time of day, the path and your own antenna matter as much. Check the bands themselves.
Source: NOAA Space Weather Prediction Center (services.swpc.noaa.gov), public domain. As of 2026-10-21 19:14 UTC.