The solar wind (particles that constantly stream outward from the sun) has a typical speed of 400 km/s. A coronal mass ejection (CME—the emission from the sun that causes Aurora) typically has a speed of 1000-2000 km/s.

The ACE satellite sits 1.4M km sunward from Earth, measuring the solar wind speed. You can see the data here: ACE SWEPAM DATA. The yellow trace shows the current solar wind speed and when this rapidly increases well above 400 km/s then the CME is 15 minutes away!