Science / Weather Glossary

Wind Direction: The direction from which the wind is blowing. For example, an easterly wind is blowing from the east, not toward the east. It is reported with reference to true north, or 360 degrees on the . . . View Full Definition

Wind Shear: The rate of wind speed or direction change with distance. Vertical wind shear is the rate of change of the wind with respect to altitude. Horizontal wind shear is the rate of change on a hor . . . View Full Definition

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 . . . View Full Definition

Wind Speed: The rate of the motion of the air on a unit of time. It can be measured in a number of ways. In observing, it is measured in knots, or nautical miles per hour. The unit most often used in th . . . View Full Definition

Wind Vane: An instrument that indicates the wind direction. The end of the vane which offers the greatest resistance to the motion of the air moves to the downwind position.

Wind Wave: An ocean or lake wave resulting from the action of wind on the water's surface. After it leaves its fetch area, it is considered a swell.

Windward: The direction from which the wind is blowing. Also the upwind side of an object. The opposite of the downwind or leeward side.

Winter: Astronomically, this is the period between the winter solstice and the vernal equinox. It is characterized as having the coldest temperatures of the year, when the sun is primarily over the . . . View Full Definition

Winter Storm: Any one of several storm systems that develop during the late fall to early spring and deposit wintry precipitation, such as snow, freezing rain, or ice.

World Meteorological Organization (WMO): From weather prediction to air pollution research, climate change related activities, ozone layer depletion studies and tropical storm forecasting, the World Meteorological Organization coor . . . View Full Definition

X-Rays: The portion of the electromagnetic spectrum that has a very short wave length. It has a wave length longer than gamma rays, yet shorter than visible light. X-rays can penetrate various thick . . . View Full Definition

Year: The interval required for the earth to complete one revolution around the sun. A sidereal year, which is the time it take for the earth to make one absolute revolution around the sun, is 365 . . . View Full Definition

Yellow Snow: Snow that is given golden, or yellow, appearance by the presence of pine or cypress pollen in it.

Zenith: The point which is elevated 90 degrees from all points on a given observer's astronomical horizon. The point on any given observer's celestial sphere that lies directly above him. The opposi . . . View Full Definition

Zodiac: The position of the sun during the course of the year as it appears to move though successive constellations. Also, the band where the ecliptic runs centrally through the celestial sphere an . . . View Full Definition

Zonal Flow: The flow of air along a latitudinal component of existing flow, normally from west to east.

Zonal Index: The measure of the strength of the westerly winds of the middle latitudes. It is expressed as the horizontal pressure difference between 35 degrees and 55 degrees latitude, or as the corresp . . . View Full Definition

Zulu Time: One of several names for the twenty-four hour time which is used throughout the scientific and military communities.

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