What causes Gusty winds? ( Meteorlogy)
Since you mention 'frontal passage' it is assumed that the term &quot;air mass&quot; is understood and also the reasons for the movement of air masses. The movement of an air mass relative to the earth's surface is what we, standing on the surface, physically feel and experience as wind.
There are things that affect the smooth flow of the air mass, such as terrain, pressure gradients, other air masses, man made obstacles etc. and these can occur at different scales. By this we mean at the continental/oceanic scale, down to the scale of human made buildings or small but significant natural outcroppings.
Localised and somewhat unpredictable short term disturbances to the smooth flow of the air mass are what we perceive as 'gusts'. Visualize it in a similar manner to the way flowing water is churned by an obstacle in its flow path and the factors that cause the churning. Try listing these factors for yourself, both for water, and for the atmospheric air.