Personal tools
  •  
You are here: Home Wildland Resources Wildland Fire Management and Planning Unit 6: Local and General Winds

Unit 6: Local and General Winds

Document Actions
  • Content View
  • Bookmarks
  • CourseFeed

::   Back

Examples of Surface Winds

In this example, the general wind at 1000 feet is west at 10 miles per hour. As this wind drops closer to the surface, its speed is reduced to 7 miles per hour by frictional drag. We will refer to this windspeed as the general wind component. The upslope wind or the local wind component is 5 miles per hour. We can add the two components together to arrive at the surface wind speed of 12 miles per hour.1

In this example, the general wind is blowing in the opposite direction and opposing the east slope wind. At the anemometer, the general wind component is stronger than the local slope wind component. The surface wind at that point would probably be the difference between the two opposing windspeeds, or a west wind at 8 miles per hour.

This example shows a nighttime situation where an inversion layer has developed in the valley. Here the general wind is confined to levels above the inversion by the stable air and therefore affects surface winds only at higher elevations. The surface wind at the anemometer will be the same as the downslope wind component.

From these examples, you can see how surface winds are dependent on time of day, position on slope, and the strength and direction of the various wind components.

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, November 08). Unit 6: Local and General Winds. 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_6__Local_and_General_Winds_7.html. This work is licensed under a Creative Commons License Creative Commons License