HF Propagation Conditions
Live shortwave and ham radio propagation report: day and night conditions for the HF bands, solar flux, geomagnetic activity and maximum usable frequency — each value explained in plain language.
HF Band Conditions
Day
Night
Global mid-latitude estimate based on worldwide solar and geomagnetic indices, not specific to your location, path or antenna. “Day” and “Night” refer to local conditions: the upper bands (17–10 m) normally close at night everywhere, while the low bands (80–40 m) open up.
Geomagnetic Field
Reported geomagnetic field condition. Quiet is best for stable HF; active or storm conditions degrade propagation.
Expected band noise level in S-units. Lower noise means weaker signals are easier to copy.
Solar Indices
Solar radio flux at 10.7 cm. Higher values raise the MUF and open the upper HF bands (10–15 m). ~70 poor, 120–150 good, 200+ excellent.
Tracks solar activity. More sunspots generally mean a higher SFI and better high-band propagation.
3-hour geomagnetic activity (0–9). 0–2 quiet (ideal), 3–4 unsettled/active, 5+ geomagnetic storm (G1–G5) that absorbs and degrades HF.
Daily geomagnetic activity, averaged from K. 0–7 quiet, 8–15 unsettled, 16–29 active, 30+ storm. High values degrade HF, especially polar paths.
Maximum Usable Frequency: the highest frequency refracted back to Earth right now. A higher MUF means the upper bands are open.
Solar X-ray class (A→X). A/B quiet, C minor; M/X flares cause daytime D-layer absorption and HF radio blackouts on the sunlit side.
Below ~400 km/s is nominal; a sustained 500–700+ can disturb the geomagnetic field and degrade HF.
Auroral activity level. Higher values mean more absorption on high-latitude and polar HF paths, while VHF aurora propagation becomes possible.
High-energy protons. Above ~10 pfu (S1) they cause polar cap absorption, blacking out HF over the poles.
High-energy electrons. Elevated values (>1000) mainly affect satellites, with limited direct impact on HF.
He I 1083 nm line: a proxy for solar activity and coronal holes rather than a direct band verdict.
How to read HF propagation data
Shortwave signals travel long distances by bouncing off the ionosphere, a layer of the upper atmosphere ionised by the Sun. How well that works depends on two things: how much energy the Sun is pouring into the ionosphere (solar flux, sunspots, X-rays) and how disturbed Earth’s magnetic field is (K and A index, solar wind). Strong solar flux with a quiet magnetic field is the best combination.
The quick check
- SFI above 120 and K-index 0–2: excellent conditions, the higher bands are likely open during daylight.
- SFI 90–120, K-index 3: average conditions; 20 m and below work reliably, 15–10 m are hit and miss.
- K-index 5 or more: geomagnetic storm. Expect weak, fluttery signals and closed polar paths regardless of the solar flux.
- M or X class X-ray flare: sudden daytime fade-out on the sunlit side of the Earth, usually lasting minutes to an hour.
Why the bands change between day and night
During the day the Sun ionises the upper F layer strongly, so higher frequencies are reflected and the upper bands open. At the same time the lower D layer absorbs the low frequencies, so 80 and 40 m are limited to short distances. After sunset the D layer disappears — the low bands open up for long-distance reception — while the F layer weakens and the upper bands close.
The grayline, the twilight band between day and night, is often the best moment for long-distance paths: the D layer has already faded while the F layer is still strongly ionised.
From ham bands to shortwave broadcast bands
The band report uses amateur radio band names, but the same physics applies to international broadcasters. Use this table to translate the report for shortwave listening:
| Report row | Broadcast bands | Frequencies |
|---|---|---|
| 80 m – 40 m | 90, 75, 60, 49, 41 m | 3.2 – 7.6 MHz |
| 30 m – 20 m | 31, 25, 22 m | 9.4 – 13.9 MHz |
| 17 m – 15 m | 19, 16, 15 m | 15.1 – 19.0 MHz |
| 12 m – 10 m | 13, 11 m | 21.4 – 26.1 MHz |
How often is this page updated?
The data is refreshed every 20 minutes. Keep in mind that most indices change slowly: the K-index is published every 3 hours, while the solar flux and sunspot number are daily values. The page refreshes itself while it stays open.
Take it with you
The same propagation panel is built into SWList and SWLStation, the shortwave listening apps for iPhone, iPad and Mac, together with live station schedules (EiBi, AOKI), a grayline world map and receiver control.
Data sources
Solar and geomagnetic data courtesy of hamqsl.com (N0NBH) and NOAA Space Weather Prediction Center. Interpretation thresholds follow those commonly used by the amateur radio community and are meant as a general guide, not a forecast for a specific path.