IonoFlux field guide
NOAA R, S and G scales
A beginner-friendly guide to NOAA space-weather scales and HF radio.
In simple terms
R describes radio blackouts from solar flares, S describes solar-radiation storms, and G describes geomagnetic storms. Zero means none; five is the most severe category.
How to read it
R is most directly related to sudden HF absorption. G describes magnetic disturbance. S is especially important for spacecraft and high-altitude systems, but can also signal an active Sun.
A practical example
An R2 event means a moderate radio blackout risk on the sunlit side. Treat it as a reason to check the path and observations, not as a universal outage.