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A rule of thumb from the flux and Kp above, not a forecast. Your latitude, antenna and local noise all beat it.
| Band | Day | Night |
|---|---|---|
| 80m | Fair | Good |
| 40m | Fair | Good |
| 30m | Fair | Fair |
| 20m | Fair | Fair |
| 17m | Fair | Poor |
| 15m | Poor | Poor |
| 12m | Poor | Poor |
| 10m | Poor | Poor |
| 6m | Poor | Poor |
The WWV bulletin, verbatim from NOAA SWPC.
:Product: Geophysical Alert Message wwv.txt :Issued: 2026 Aug 10 0605 UTC # Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center # # Geophysical Alert Message # Solar-terrestrial indices for 09 August follow. Solar flux 94 and estimated planetary A-index 7. The estimated planetary K-index at 0600 UTC on 10 August was 1.00. No space weather storms were observed for the past 24 hours. No space weather storms are predicted for the next 24 hours.
Source: NOAA Space Weather Prediction Center, services.swpc.noaa.gov — public domain.
That happens, and it is worth posting about. Compare notes on the Propagation board at the Ham Radio Forum, or read the propagation guide.
Solar flux (SFI) measures radio noise from the sun at 10.7 cm and stands in for how strongly the F2 layer is ionised. Higher flux means the F2 layer supports refraction at higher frequencies, so the upper HF bands open and stay open longer. Below about 70 the high bands are mostly shut; above about 150 the 15, 12 and 10 metre bands come alive.
Kp is a planetary index of geomagnetic disturbance on a 0–9 scale. Low Kp means a quiet field and stable paths. High Kp means a geomagnetic storm: absorption rises, polar and high-latitude paths degrade first and worst, and the auroral oval pushes south — which is bad for HF and, at the same time, the thing that opens 6 metre and 2 metre auroral scatter.
The band table is a rule of thumb, not a forecast. It combines flux and Kp the way most propagation widgets do, and it is wrong regularly — the ionosphere is not uniform, your latitude and antenna matter enormously, and a band that the table calls poor can still be open on one path. Treat it as a starting point and trust your receiver over it.
The page is rebuilt from NOAA SWPC data on a schedule and the timestamp above shows when. It is not live to the second, and it does not need to be — solar flux is reported daily and the planetary K-index in three-hour intervals, so a page that refreshed every minute would show the same numbers.
Because the table is a global rule of thumb and propagation is a path. Flux and Kp describe the average state of the ionosphere, not the specific path between you and the other station. Short skip, sporadic-E, a good antenna and a quiet local noise floor all beat the index. If you are making contacts, the band is open, whatever the table says.
They track each other closely but measure different things. Sunspot number counts visible spots and groups; solar flux measures actual radio emission at 10.7 cm, which is a more direct proxy for the ionising radiation that matters to us. Flux is the more useful of the two for propagation, which is why it leads here.
Not for everything. It degrades HF, particularly on high-latitude and polar paths, and it can black out the higher bands entirely during a severe storm. But the same disturbance drives the auroral oval south and opens auroral scatter on 6 and 2 metres, and it is the reason anyone ever hears aurora-mode signals at all. Which effect matters depends on the band you are on.