CHARACTERISTIC | TYPICAL | UNUSUAL |
|---|---|---|
Time of year | Apri | Winter |
Time of day | 4:00 to 6:00 p.m. | Early morning |
Diameter | 50 m (160 ft) | 1.5 km (1 mi) |
Forward movement speed | 48 km/h (30 mph) | 113 km/h (70 mph) |
Length of ground path | 3 km (2 mi) | 480 km (300 mi) |
Duration | 5 minutes | Up to 6 hours |