Page:Handbook of Meteorology.djvu/185

 Cirro-stratus clouds covering the western horizon to a height of 30 degrees or more indicate rain within twelve hours as a rule. This is a still more certain indication if the lower edge of the cloud is wavy. A cirrus patch with streamer edges, which increases in size, indicates snow.

Clouds moving apparently against a surface wind in reality are moving with an upper current of the air. That is, crosswinds are blowing, and cross-winds very commonly precede rain or snow; a departing storm may also clear with crosswinds.

When ye see a cloud rise out of the west, straightway ye say: There cometh a shower; and so it is.—

The greasy, gray clouds which are characteristic of tropical skies during the rainy season are sometimes seen during summer in northern latitudes. They are pretty certain to indicate a heavy downpour.

If detached clouds increase in size the moisture of the air also is increasing; if they decrease in size and disappear the moisture is decreasing. While the former condition in itself does not indicate an approaching storm, it is instructive in connection with other local indications.

Animal and Plant Indications.—To assert that four-footed animals, birds, and insects sometimes foretell approaching weather conditions is to make a very radical claim which cannot