HF Propagation Forecast & Solar Data

Monitor real-time solar conditions and HF propagation forecasts. Check solar flux, K-index, sunspot numbers and band conditions to plan your next QSO.

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What the solar numbers actually mean

Solar flux, measured at 10.7 centimetres and quoted in solar flux units, is the best single indicator of how well the higher HF bands will work. A flux below about 70 leaves 10 and 12 metres largely closed, values between 90 and 130 open them for regular daytime DX, and anything above 150 can keep 10 metres alive into the evening. The sunspot number tracks the same underlying activity and moves roughly in step with it.

The K index measures disturbance in the earth magnetic field on a scale from 0 to 9, updated every three hours. Values of 0 to 2 mean quiet conditions and stable paths. From K4 upward the ionosphere becomes disturbed, paths that cross high latitudes degrade first, and at K6 and above polar routes can close entirely while the lower bands become noisy. The A index is a daily average of the same disturbance, so it tells you whether the whole day has been settled or unsettled.

Which band to use and when

As a rule of thumb the higher bands follow the sun. Ten, twelve and fifteen metres are daytime bands that need decent solar flux and normally close after dark. Twenty metres is the workhorse, usually open somewhere in the world around the clock. Forty metres becomes useful in the late afternoon and is reliable all night, while eighty and one hundred and sixty metres are night bands that suffer heavily from summer static. When the K index rises, drop down a band rather than giving up.

Frequently asked questions

What is a good propagation score for DX?

Anything above 75 means the bands should be in good shape and even SSB will get out. Between 55 and 75 is workable with CW or FT8. Below 35, weak-signal digital modes are the only reliable option. The score combines solar flux, geomagnetic activity, flare level, solar wind and your local grey line into a single figure.

What is a good solar flux index for 10m?

10m generally needs a solar flux index above about 150 for reliable worldwide F2 openings, and above 200 the band can stay open for most of the daylight hours. Below 100 the band is usually limited to sporadic E in season and short skip.

Does a high K-index kill HF propagation?

A K-index above 5 indicates a geomagnetic storm and will badly degrade HF, especially on paths crossing the auroral zone and the poles. The high bands lose their maximum usable frequency first, while the low bands suffer raised noise. A K-index below 3 is quiet and best for DX.

What is the grey line and why does it matter?

The grey line is the twilight band between day and night that sweeps around the Earth. For roughly an hour either side of your sunrise and sunset the D layer, which absorbs low band signals during the day, decays faster than the F layer. That short window often gives exceptional 160m, 80m and 40m DX.

How often is the propagation data updated?

Solar and geomagnetic figures come directly from the NOAA Space Weather Prediction Center and refresh every ten minutes on this page. The planetary K-index itself is published every three hours, while solar wind and X-ray readings update every few minutes.