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About This Service

Where the numbers come from, how the HF band estimates are calculated, how often everything updates and what the limits are.

Data sources

Data	Source
Solar flux (10.7 cm), sunspot number, daily indices	NOAA SWPC, observations from Penticton and the SWPC daily solar indices
Kp index, predicted Kp	NOAA SWPC planetary K-index products
X-ray flux	NOAA GOES primary satellite, 0.1-0.8 nm channel
Solar wind speed, density, magnetic field (Bz, Bt)	NOAA real-time solar wind (DSCOVR / ACE and successors)
3-day forecast and alerts	NOAA SWPC forecast and alert products
Solar and aurora images	NASA SDO, ESA/NASA SOHO, NOAA SWPC

NOAA SWPC data is provided by a US government agency for public use. Images belong to their respective sources and are loaded directly from their servers.

How the HF band estimates work

The estimates use a deliberately simple model, so you can understand and check them:

The daytime maximum usable frequency is approximated from the solar flux: MUF_day = 8 + 0.12 × SFI (MHz). At night it is taken as 0.65 × MUF_day.
For each band, the ratio between the MUF and the band frequency sets the base level: ratio 1.2 or more is Good, 0.7 to 1.2 is Fair, below 0.7 is Poor.
In daylight, D-layer absorption limits the bands below 8 MHz to Fair, and the bands below 4 MHz to Poor.
Geomagnetic disturbance lowers every band by one level at Kp 5 or more (two levels at Kp 7 or more). At Kp 4, only the night-time low bands are lowered.
A flare of class M5 or stronger (R2) lowers all daytime bands by one level; X1 or stronger (R3) lowers them by two.

The four band groups (80-40, 30-20, 17-15, 12-10 m) use a representative frequency for each group; the band-by-band table uses the centre of each amateur band. You can experiment with the model in the what-if simulator.

Limits

The model ignores the season, the latitude, the exact path, antennas and power, and the local noise level. Real propagation can be better or worse.
It cannot see sporadic-E, which is why the VHF outlook only shows a seasonal likelihood.
The solar flux is measured daily; values shown between measurements are the latest published.
This is an educational and planning aid, not a professional ionospheric forecast. Real-time spots from reporting networks remain the best proof of a band opening.

Updates

Data is fetched from NOAA on demand at most once every 5 minutes and shared by every page. If a source is temporarily unavailable, the last valid values are shown and a notice appears on the live pages.

About the author

This section is part of Map For HAM, created and maintained by Diego Rispoli, IU1FIG.

Data: NOAA Space Weather Prediction Center, NASA SDO. Band conditions are estimates computed by Map For HAM and are indicative only. Methodology and credits · Data feeds · Widgets