HF-band conditions (day/night)

These are the values I calculated from the raw NOAA data. There isn’t any golden rule for calculation propagation conditions. I’ve put together an algorithm based on data from different sources. As a rule of thumb, values below 40 are considered poor, between 41 and 89 fair and above 89 good.
Paul Herrman (N0NBH) has a fantastic site if you’re into solar and weather data. I’ve used his info a lot.