Page:Handbook of Meteorology.djvu/117

 In the present state of human knowledge, forecasts of hail-storms cannot be made. The Weather Bureau is making efforts to gain all possible information concerning date, time, duration, extent of area and path of hailstorms. It is pretty well established, however, that hailstorms are more frequent in certain regions than in others; and that in certain limited areas in these regions of greatest frequency they are more destructive than in other areas.

Cloudbursts.—The cloudburst is an excessive downpour of rain, in which the water seems to fall in masses rather than in drops. Cloudbursts are rare; the area covered is small; the duration is a matter of a few moments only. Only in a few cases have trustworthy measurements of the amount of precipitation been made. The ordinary barrel gauge would probably give a result at least 80 per cent true. The majority of recording gauges are of but little use in such storms. Moreover, the cloudburst does not always select for its performance a locality where Weather Bureau stations are in evidence.

The origin of the cloudburst is not certainly known. To call it an exaggerated thunder-storm may express a truth in some cases; certainly not in every case. All the water in an overhead saturated air at a temperature of 70° F over the area covered by the downpour would not make a rainfall sufficient to account for the water dropped by a cloudburst.