When a layer of cloud rolls or clumps extends in long lines that stretch off to the horizon, the effect of perspective makes these lines converge, like railway tracks, towards a point. Such a formation is a variety known as radiatus, and it can be found in low-, mid- and high-level clouds.

When radiatus formations appear in low clouds, such as the Cumulus clouds shown here, the long lines are known as ‘cloud streets’. These tend to cause glider pilots to wet themselves with excitement, for they act as avenues of lifting air along which a glider can reliably gain altitude.