This graph shows the strength of solar wind power, a real-time indicator of how strong aurora will be in about one hour. The solar wind power corresponds to the energy released by the sun over time. The more energy released, the higher the power and the stronger the aurora will be.

The solar wind power is measured by the ACE satellite just upstream of Earth and reported in units called gigawatts (1 GW = 1 billion watts). Use the following guidelines to see if an aurora might be visible in your area.

• Less than 50 GW: Minor aurora at high latitudes only
• 50 GW: Small substorm visible at high latitudes (perhaps in Alaska, Canada, or northern Scandinavia)
• 200 GW: Small storm visible at mid and high latitudes (possibly the US/Canadian border, southern Scandinavia, or northern UK)
• 1000+ GW: Medium storm visible at mid-latitudes (into the northern US/UK)
• 3000+ GW: Large storm visible in the central to southern US and UK
• Sustained increases in solar wind power for at least half an hour are more likely to yield the corresponding storm level. Storms of increased (but still highly variable) auroral activity can last from less than a day to a day or more.