Dry Line
The boundary between the dry desert air mass of the Southwest U.S. and the moist air mass from the Gulf of Mexico. It usually lies north-south across the central and southern High Plains states during spring and summer. The passage of a dry line results in a sharp decrease in humidity, clearing skies, and a wind shift from southeasterly or south to southwesterly or west. Its presence influences severe weather development in the Great Plains.
Air Mass
An extensive body of air throughout which the horizontal temperature and moisture characteristics are similar.
Moisture
Refers to the water vapor content in the atmosphere, or the total water, liquid, solid or vapor, in a given volume of air.
Spring
The season of the year which occurs as the sun approaches the summer solstice, and characterized by increasing temperatures in the mid-latitudes. Customarily, this refers to the months of March, April, and May in the North Hemisphere, and the months of September, October, and November in the Southern Hemisphere. Astronomically, this is the period between the vernal equinox and the summer solstice.
Summer
Astronomically, this is the period between the summer solstice and the autumnal equinox. It is characterized as having the warmest temperatures of the year, except in some tropical regions. Customarily, this refers to the months of June, July, and August in the North Hemisphere, and the months of December, January, and February in the Southern Hemisphere.
Humidity
The amount of water vapor in the air. It is often confused with relative humidity or dew point.
Related terms: absolute humidity, relative humidity, and specific humidity
Sky
The vault-like apparent surface against which all aerial objects are seen from the earth.
Wind Shift
The term applied to a change in wind direction of 45 degrees or more, which takes place in less than 15 minutes. It may the result of a frontal passage, from katabatic winds, sea breezes, or thunderstorms, and in some instances, the change may be gradual or abrupt.
Severe Weather
Generally, any destructive weather event, but usually applies to localized storms, such as blizzards, intense thunderstorms, or tornadoes.