Ray (NM2O) has provided a link to the “Near-Real-Time F2-Layer Critical Frequency Map” website. The website shows the Critical Frequency. This information supplements the band conditions, flux, K, etc. graph to the left.
The definition of Critical Frequency is: The highest frequency that is returned when a signal is sent straight up. To work in close on HF, you need to be below the critical frequency.
The Space Weather site generates a new plot every 10 minutes or so. The plot takes into account the solar flux, the K index, the time of day and the date.
