Science for beginners . e side ofyou; d and df show the narrow strips of country covered by somethunderstorms. These are top views. storm behind it, may advance broadside toward us, as in (a)(Fig. 138). They may pass by to one side, as in (6) or (c).They may travel endwise over a narrow strip of sky, as in(d). They may come obliquely (on a slant), as in (e). Thehigh advance cloud may be thin at first, so the sun can be seenthrough it. Before long it becomes thicker and , back toward the horizon that it is coming from, youcan see the dense black, or greenish-black, base of the stor
Science for beginners . e side ofyou; d and df show the narrow strips of country covered by somethunderstorms. These are top views. storm behind it, may advance broadside toward us, as in (a)(Fig. 138). They may pass by to one side, as in (6) or (c).They may travel endwise over a narrow strip of sky, as in(d). They may come obliquely (on a slant), as in (e). Thehigh advance cloud may be thin at first, so the sun can be seenthrough it. Before long it becomes thicker and , back toward the horizon that it is coming from, youcan see the dense black, or greenish-black, base of the storm 182 THE WEATHER cloud; then the gray, or dark blue, curtain of rain fallingfrom it. Often just in front of the rain is a roll or bankof ragged grayish cloud that is tumbled and tossed by thewind. This is called the squall cloud, and immediatelyafter it usually comes the first dash of heavy rain. The rainmay last from a few minutes to an hour or two, and may besteady or broken. Toward the last it usually slackens grad-. y mmm Fig. 139.—Diagram of a thunderstorm. A, B. Warm air flowing into and up through the cloud, largely fromin front but often also from sides. D. Downward movement of air within a portion of the storm. Z. Cirro-stratus advance extending often far in front. M, N, R. Lower clouds in front of storm; almost any size and amountmay be present. G. Outflowing wind of storm front. X. Squall cloud, a ragged roll mixing and tumbling; not alwayspresent. T. Front of main cloud. H, K. Points mentioned in discussing hail. V. Backward flow of air in rear of storm; not always present. ually until it stops. Not long after the rain ends, and some-times before it ends, the clouds begin to break. About oneto three hours later, especially if it is toward evening, youcan sometimes see in the east the brilliantly lighted tops ofthe departing storm cloud. The tops of cumulo-nimbus re-flect the light of the setting i Sometimes the sun may set clear while a sheet of storm cloud
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectscience, bookyear1921
