FLOOD02838

• County: Douglas
• County: Arapahoe
• Community: Greenwood Village, Aurora
• Stream Name: Cherry Creek
• Basin: South Platte
• Title: Probable Maximum Precipitation Study for Cherry Creek Reservoir - Final Report
• Date: 8/1/2003
• Prepared For: CWCB
• Prepared By: CWCB
• Floodplain - Doc Type: Project

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GLOSSARY

Advection: The process of transfer (of an air mass property) by virtue of motion. In particular
cases, advection may be confined to either the horizontal or vertical components of the motion.
However, the term is often used to signifY horizontal transfer only.

Air mass: Extensive body of air approximating horizontal homogeneity, identified as to source
region and subsequent modifications.

Barrier: A mountain range that partially blocks the flow of warm humid air from a source of
moisture to the basin under study.

Basin shape: The physical outline of the basin as determined from topographic charts or field
survey.

Cold front: Front where relatively colder air displaces warmer air.

Convective rain: Rainfall caused by the vertical motion of an ascending mass of air that is
warmer than the environment and typically forms a cumulonimbus cloud. The horizontal
dimension of such a mass of air is generally of the order of 12 miles or less. Convective rain is
typically of greater intensity than either of the other two main classes of rainfall (cyclonic and
orographic) and is often accompanied by thunder. The term is more particularly used for those
cases in which the precipitation covers a large area as a result of the agglomeration of
cumulonimbus masses,

Convergence: Horizontal shrinking and vertical stretching ofa volume of air, accompanied by
net inflow horizontally and internal upward motion.

Cooperative station: The location of a weather observation site where an unpaid observer
maintains a climatological station for the National Weather Service.

Cyclone: A distribution of atmospheric pressure in which there is a low central pressure relative
to the surroundings. On large-scale weather charts, cyclones are characterized by a system of
closed constant pressure lines (isobars), generally approximately circular or oval in form,
enclosing a central low-pressure area. Cyclonic circulation is counterclockwise in the northern
hemisphere and clockwise in the southern. (That is, the sense of rotation about the local vertical
is the same as that of the earth's rotation,)

Dewpoint: The temperature to which a given parcel of air must be cooled at constant pressure
and constant water vapor content in order for saturation to occur.

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