The waves are heard as a single thunder crash when the lightning bolt is straight and short. When the bolt is long and forked, there is a succession of crashes and rumbles. To judge how close lightning is, count the seconds between the flash and the thunder clap. Each second represents about 300 m. Hail Hail is formed when updrafts in thunderclouds carry raindrops upward into extremely cold areas of the atmosphere, where they freeze and merge into lumps of ice. When the lumps become too heavy to be supported by the updraft, they fall to the ground at high speeds.
Hail can be extremely dangerous, particularly when accompanied by strong winds.
Cathy Anker Hail stones gathered up after the storm that hit Thornhill, Ontario in 1981. Thunderstorm detection at Environment Canada Weather Radar Weather radar is a prime tool of Environment Canada in detecting heavy precipitation, rapidly developing cloud systems, and other signatures of severe thunderstorms. Weather radars cover the areas inhabited by 95 per cent of Canada's population. Each radar scans a radius of about 325 km, although the best range for detecting thunder clouds is 120 to 150 km. Just as a searchlight beam picks out and reflects off an object, weather radar sends out microwave pulses that bounce off rain, hail and snow.