Attachment 5
A5.3.2.2.4. Forest Service
A5.3.2.2.5. Soil Conservation Service
A5.3.2.2.6. Federal Aviation Administration
A5.3.2.2.7. Army Corps of Engineers
A5.3.2.2.8. Navy Oceanographic Office
A5.3.2.2.9. Geological Survey
A5.4. Wind Velocity and Direction. The following are the most important meteorological factors
determining runway orientation:
A5.4.1. Composite Windrose. When weather recording stations are located near a proposed site and
intervening terrain is level or slightly rolling, prepare a composite windrose from data of surrounding
stations.
A5.4.2. Terrain. If intervening terrain is mountainous or contains lakes or large rivers, allow for their
effects on wind velocities and directions by judgment, after study of topographical information and
available meteorological data.
A5.4.3. Additional Weather Data. Consider wind directions and velocities in conjunction with
visibility, precipitation, and other pertinent weather information.
A5.4.4. Wind Distribution. Determine wind distribution to accompany Instrument Flight Rule (IFR)
conditions when considering orientation of an instrument runway.
A5.5. Use of Windrose Diagrams. Prepare a windrose diagram for each new runway in the planning
stage or to analyze the operational impact of wind on existing runways.
A5.5.1. Drawing the Windrose. The standard windrose (Figures A5.1 and A5.2) consists of a series of
concentric circles cut by radial lines. The perimeter of each concentric circle represents the division
between successive wind speed groupings. Radial lines are drawn so that the area between each
successive pair is centered on the direction of the reported wind.
A5.5.2. Special Conditions. Windrose diagrams for special meteorological conditions, such as wind
velocities and directions during IFR conditions, should be prepared when necessary for local airfield
needs.
A5.5.2.1. Wind Direction. Use radial lines to represent compass directions based on true north,
and concentric circles, drawn to scale, to represent wind velocities measured from the center of the
circle.
A5.5.2.2. Calm Wind. Use the innermost circle to encompass calm periods and wind velocities up
to the allowable crosswind component for the airfield under consideration.
A5.5.2.3. Computations. Compute percentages of time that winds of indicated velocities and
directions occur, and insert them in the segments bounded by the appropriate radial direction lines
and concentric wind velocity circles. Express percentages to the nearest tenth, which is adequate
and consistent with wind data accuracy. Figure A5.3 displays a completed windrose.
A5-2
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