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How to Figure the Daily Dominant Wind Direction

At any given moment, the wind is likely to be be blowing from any direction. There is, however, for most areas, a dominant daily wind direction. This direction is verified by averaging momentary wind readings at a given location throughout the day. The more readings taken, the more accurate the average daily dominant wind direction will be. Modern wind vanes are often connected to computers and take regular readings continuously throughout the day. You will determine the dominant daily wind direction by making a ribbon wind vane, taking periodic readings throughout the day and averaging your daily data.

Things You'll Need

3-foot broomstick or 3/4-inch wooden dowel
24-inch piece of 1/4- to 1/2-inch-wide ribbon
24-inch square or round 3/4 plywood base
Indelible marking pen
3-inch finishing nail
3-inch drywall screw
Compass
Notebook

Instructions

- 1
  
  Use a directional compass to mark your wind vane base in degrees and to orient your wind vane in the field.
  
  Make the base for your wind vane using a 2-foot square or round piece of 3/4-inch thick plywood. Find the exact center of the base by drawing two diagonals or two diameters at right angle to each other through the center of the base. Use these lines as cardinal compass directions, but instead of letters (NSEW) print compass bearings in degrees for each direction: 0=N, 90=E, 180=S, 270=W and 0 or 360 degrees takes you back to North. Use a directional compass or a protractor to find the next set of bearings for NE=45, SE=135, SW=225 and NW=315 degrees respectively.
- 2
  Attach a 3-foot broomstick or dowel directly to the exact center of the base using a 3-inch drywall screw. This connection needs to be good and tight, but be sure both pieces are centered and make certain the broomstick or dowel does not split by turning the screw slowly and straight.
- 3
  Carefully center the 3-inch finishing nail over the top end of the broomstick or dowel and hammer it in gently so it remains centered and sticks up about 1.5 inches. Make certain the shaft of the nail is not corroded, but is smooth and shiny to allow the knot of ribbon to spin freely around the nail in the wind.
- 4
  Tie the 24-inch piece of ribbon to the finishing nail using one good tight overhand knot followed by another knot and leaving as little excess as possible. Be sure that the knot spins freely on the nail but is not able to blow off. This completes your ribbon wind vane.
- 5
  Place your wind vane in an open outdoor area accessible to you for taking regular readings, but not protected or sheltered from the wind in any way. Use a compass to orient your wind vane so that 0 degrees North is pointing toward true North.
- 6
  Decide how many readings you will take each day. The more readings the better. Readings should be evenly spaced in time for greatest accuracy. If you take hourly or half hourly readings, record the date, the time, and the direction the ribbon is blowing in degrees. Then record the exact 180-degree opposite direction because that is the direction the wind is actually coming. If the ribbon points 45 degrees northeast, then the actual direction the wind is coming from is 225 degrees southwest.
- 7
  Continue taking regular readings throughout the day according to your schedule. At the end of each day add up all of the readings. Then divide the sum by the number of readings you took that day. The number you get is your daily dominant wind direction based on the average of the data you collected for that day.

Nature