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Unit 4: Temperature-Moisture Relationship

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Temperature & Heat   ::   Temperature & Altitude   ::   Atmospheric Moisture   ::   Relative Humidity   ::   Clouds   ::   Exercises

Clouds and Fire Weather

The last part of this unit addresses clouds and their effect on fire weather. Clouds, consisting of many minute water and/or ice particles in the atmosphere, are the result of condensation of water vapor in air. Clouds are classified according to levels or heights of their bases in the atmosphere.

Clouds : consisting of many minute water and/or ice particles in the atmosphere, are the result of condensation of water vapor in air.

Classifying Clouds

Clouds are classified according to levels or heights of their bases in the atmosphere as follows:

  1. High or cirro : Clouds that develop bases above 20,000 feet including cirrus, cirrocumulus, and cirrostratus.
  2. Middle or alto : Clouds that develop bases between 6,500 and 20,000 feet including altocumulus, altostratus, and nimbostratus.
  3. Low or strato : Clouds that develop bases from near the ground to 6,500 and 20,000 feet including altocumulus, altostratus, and nimbostratus.
  4. Vertical development : Clouds with bases that range from 1,500 feet to 10,000 feet, and tops to 50,000 feet including cumulus and cumulonimbus.
  5. Fog : Cloud-like in nature but forming at and touching the surface or the ground.

Cloud Development Processes

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How do clouds develop? There are two principal ways in which air can reach its saturation point and cause clouds to form. One is through the addition of moisture to the air, and the other through lowering of air temperature to its dew point.

Kinds of Clouds In The Atmosphere

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Several clouds are especially important to the firefighter. Some of these can have detrimental effects on a fire. Other clouds, called indicator clouds, aid the firefighter. Recognizing them early may help firefighters to anticipate weather to follow. Some of the clouds described in this part can produce precipitation, which usually aids the fire manager.

Lifting Processes in the Atmosphere

The most important cooling method is by lifting of air. Lifting can be accomplished in these ways--thermal, orographic, or frontal action. These processes produce most clouds. Lifting processes will be discussed more in Unit 7 on atmospheric stability and instability.

  1. Thermal lifting.
  2. Orographic lifting.
  3. Frontal lifting.

Stages of Cumulus Cloud Development

Stage 1 Stage 2
Stage 3 Stage 4

The growing cumulus clouds sometimes develop into mature thunderstorms under the right environmental conditions.

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, October 27). Unit 4: Temperature-Moisture Relationship. Retrieved January 07, 2011, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/Forest__Range__and_Wildlife_Sciences/Wildland_Fire_Management_and_Planning/Unit_4__Temperature-Moisture_Relationship_6.html. This work is licensed under a Creative Commons License Creative Commons License