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a short note on variable winds
A condition when (1) the wind direction fluctuates by 60 degrees or more during the 2-minute evaluation period and the wind speed is greater than 6 knots; or (2) the direction is variable and the wind speed is 6 knots or less
or

When the wind is strong, it is an indication there is a strong pressure gradient in the troposphere. The wind, due to its strong momentum, tends to resist changing directions (unless friction produces turbulence). Wind direction is best detected in an open area away from surface obstructions such as buildings and trees. When the pressure gradient becomes weak, the small mesoscale and microscale environment overpowers the synoptic scale influence on wind direction. Influences such as thermal eddies, subtle density boundaries, cool air drainage into lower elevations, mixing down of slightly stronger winds aloft, and thermal boundaries (urban islands, vegetation islands) influence wind direction more than the synoptic scale pressure gradient.


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