METEOROLOGIST JEFF HABY
The phrase, "the wind will be light and variable" is a familiar one. Why does wind tend to be variable when
wind speeds are low? 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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