How to Caculate the Wind Direction

Calculating wind direction helps predict the weather.

Wind direction influences upcoming weather, and knowing the direction of the wind aids with weather forecasting. A wind direction atypical for the season and location signals changing weather. In the northern hemisphere, winds from the north generally bring in colder air, and warmer air flows with winds from the south. Abrupt changes in wind direction are caused by frontal passages or thunderstorm activity. Winds passing over large bodies of water can bring humidity, rain or "lake effect snow."

Things You'll Need

• Wind vane
• Compass

Instructions

1. 

   Align the magnetic needle of the compass to N (north).

   Align the compass with the end (usually red) of the magnetic needle pointing N (north). North is also called both 0º and 360º. Use the compass to align the directions on the wind vane.

2. 

   A quick study of the compass makes reading wind direction easier.

   Study the face of the compass. Note the cardinal points indicated by the letters N (north), E (east), S (south) and W (west). Halfway between each cardinal point are intercardinal points indicated by the letters NE (northeast), SE (southeast), SW (southwest) and NW (northwest). Halfway between each cardinal and intercardinal point are secondary intercardinal points. These are NNE (north-northeast), ENE (east-northeast), ESE (east-southeast), SSE (south-southeast), SSW (south-southwest), WSW (west-southwest), WNW (west-northwest) and NNW (north-northwest). More precise readings in degrees are on many compasses.

3. 

   Directions appear as letters on the face of the compass.

   Read the wind direction using the directions (letters) on the compass. The arrow of the wind vane points to the direction from which the wind is blowing. If the arrow of the wind vane points to SE (southeast), the wind is from the southeast, blowing toward the NW (northwest). If a reading falls between directional markings, use the direction that is closest.

4. 

   Degree markings on the compass are more precise than estimating the direction.

   Read the wind direction using degrees. Add 180º to readings of 180º or less. Subtract 180º from readings over 180º. Using the example in Step 3, SE is 135º on the compass. Since 135º is less than 180º, add 180º to 135º to determine that the wind is blowing toward 315º, which is NW. If the wind blows from 225º, subtract 180º to determine the wind is blowing to 45º, which is NE.

References

• TheWeatherPrediction.com: Wind Direction and Weather Forecasting
• Wisconsin Department of Natural Resources: Reading a Compass and Orienteering
• Center for Analysis and Prediction of Storms: Activity 8, How to Read the Wind Vane
• Rutgers Marine and Coastal Sciences: Understanding Wind Direction