This is a rule-of-thumb model: higher solar flux opens the higher bands in daylight; geomagnetic disturbance (Kp) degrades everything, polar paths first. It won't replace a full ionospheric prediction, but it will tell you where to start listening.
- SFI (solar flux index) tracks the ionization that HF skywave depends on. Below ~90 the bands above 20m struggle; above ~150, 10m comes alive.
- Kp measures geomagnetic disturbance: 0–2 quiet, 3 unsettled, 4 active, 5+ is a storm — expect weak, watery signals and dead polar paths.
- Gray line: the model adds a bump to 80/40/30m near your sunrise and sunset — long-haul DX along the terminator is real and worth chasing.
- 6m is sporadic-E, not solar flux: openings appear mostly in early summer regardless of these numbers. The planner shows the seasonal window only.
- The far end matters too — a band must be open at both ends of the path. For DX, think about the other station's local time.
- Live numbers from NOAA SWPC, refreshed every 15 minutes. You can type in your own SFI/Kp to play "what if".