Space weather
Reading the scales
A source-linked guide to NOAA scales, Kp, and the difference between observations and forecasts.
READING THE SCALES
Different disturbances.
Different effects.
NOAA’s G, R, and S scales describe different phenomena. Level 0 here means below the first scale threshold, rather than a promise about every radio path.
G / geomagnetic storms
Disturbances in Earth’s magnetic field can affect HF propagation, satellite navigation, and aurora. The numbered storm scale starts at G1.
R / radio blackouts
These events are associated with solar X-ray flares and can disturb HF communication on Earth’s sunlit side. They are distinct from geomagnetic storms.
S / solar radiation storms
Elevated energetic-particle levels can affect spacecraft and radio communication in polar regions. NOAA tracks them on a separate scale.
Delayed or missing data
The page labels delayed readings and shows source times. A failed feed displays Unavailable. The current scale cards use observed readings, while the aurora map is explicitly a forecast.