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.[1] 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.
- ↑ A mining engineer in Arizona relates the following: “The day, up to 3 o’clock, had been moist—to the extent that distant objects possessed atmosphere—that is, there was not the illusion of nearness which a very dry air gives. In mid-afternoon there came a sudden darkening of the sky, a light patter of rain, and then a downpour so torrential that further progress along the trail was out of question. The loose rockwaste seemed to be washed out from under the horse’s hoofs, and a boss of rock near by seemed to be the only safe place. It was impossible to see anything more than a few rods ahead. The downpour lasted for not more than fifteen minutes. To say that the amount was 6 inches is merely a guess. Much of the trail was washed away and badly gullied. Pinal Creek was a roaring torrent; to have attempted crossing it would have been instant death. Across the summit, on the other side of the range, not a drop of rain fell.”
Another traveler wrote: “A heavy cloud had been hovering over Pilot Range for several hours, and we were not surprised to hear a low moan which soon became a roar. So we climbed out of the arroya in quick time. In a very few moments, there came a torrent that would have carried a ton boulder down the course. The cloud over Pilot Knob had dropped its shower and the sink below was full of water—the first time, perhaps, in fifty years.”
