Page:Handbook of Meteorology.djvu/180

 During a period of low pressure, fine weather may be regarded with suspicion; a change may he expected at any time and most likely it will be sudden.

The barometer falls lower for high winds than for rain, but torrential rains may accompany a very low pressure. In winter, if high temperature accompanies very low pressure, heavy rain followed by a cold wave may be expected.

A rising barometer usually indicates winds having a westerly element—southwest, west, or northwest. A falling barometer usually indicates winds having an easterly element—southeast, east, or northeast. The rule is not infallible, however. Occasionally there occurs a dry east wind with a rising barometer.

A gradual but steady fall of the barometer indicates unsettled weather, increasing moisture and rain. A slow fall from a very high barometer indicates unsettled and rainy conditions rather more certainly. A sudden and rapid fall indicates a sudden downpour and high winds, or both. In summer a thunder-storm is preceded usually by a drop in pressure.

Wind Indications of Weather Conditions.—Throughout the eastern half of the United States winds with a westerly element—northwest, west, and southwest winds—indicate fair weather. Winds with an easterly element—northeast, east, and southeast winds—indicate unsettled weather, rain or snow.

A straight north wind is apt to be a clear- weather wind. “The north wind driveth away rain.”—; but this is not always true, especially if it veers into the northeast.

Straight south winds along the Atlantic and Gulf Coasts are apt to bring unsettled weather, inasmuch as the south wind blows from the sea, it usually brings warm air and excessively humid weather. Occasionally it brings storm conditions.

West winds are dry winds; in the eastern half of the United States they are apt to be dust-laden also. In midsummer they blow many miles over sun-heated ground and they are therefore apt to be hot winds.

East winds almost always precede rain and snow by twenty-four hours or more. Along the Atlantic Coast the east wind is pretty certain to be a storm-breeder.