ClipArt ETC
"The warmer current ascends, as indicated by the small arrows, and curls at the black wreath (u) of cloud, and then the commingling of the two currents forms an imposing dark dome (v) of cloud, from which heavy rain (r) or hail descends. The light grayish cloud which is seen behind the black wreath is the rain descending from the dark dome. The heavy raindrops bring down a large quantity of cold air, which flies straight out in advance of the storm, and produces the squall (q) indicated by the long arrow."—Finley, 1917

Line squall

"The warmer current ascends, as indicated by the small arrows, and curls at the black wreath (u) of…