CLOUDBURST. A term first applied in the United States about 1810, and in India about 1860, to a sudden extraordinarily heavy local rain. No definite rate or amount of rainfall, or area covered by it, has been assigned as a limit proper for distinguishing cloudbursts from ordinary heavy rains. Many special eases of cloudbursts have been described in English and American meteorological journals, especially in the United Monthly Review, from which it may be seen that the term is rarely used unless six or more inches of rain fall, and at the rate of 10 or more inches per hour. Thus, in one case, 10 inches fell in an hour; in another, the extreme ease, 21 inches. Nothing definite is known as to the areas cov ered by these heavy rains; but it is not likely that the heaviest cover more than an acre, or that the lighter ones cover more than a square mile. Several cloudbursts have occurred on the eastern slope of the Rocky Mountains; hut the great rains that cause the heavy floods along the eastern slope of the Appalachians from Georgia to Pennsylvania sometimes attain the intense local character that is ordinarily at tached to the term cloudburst. Professor Ferrel
has explained how a mass of water can he held within the cloud by means of rapidly ascending currents; hut there is scant evidence of the actual existence of the strong ascending wind required by this explanation, and it seems equally possible that cloudbursts may result from the sudden formation of a large mass of rain in a very tall cloud, rather than from the gradnal accuinulation of rain in the clouds. Consult: Ferrel, Recent Advances (Washington, 1885), and his Popular Treatise on the Winds (New York, 1893).