Microfronts are common at our sites particularly at sites with at least some topography.  Microfronts lead to unpredictable sharp changes of temperature and wind direction shifts.  Microfronts become problematic with short term forecasts of frost potential, ice formation and local transport of atmospheric contaminants.

The following video visualizes propagation of several contrasting micro fronts.

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Moments later a reverse eddy forms at the top of the microfront with counter-clockwise rotation, as has been observed in laboratory flows for decades.
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Moments later a reverse eddy forms at the top of the microfront with counter-clockwise rotation, as has been observed in laboratory flows for decades.

 

The use of a drone provides valuable addition information.  Videos from drones reveal the horizontal extent and coherence of the microfronts.  An example of two microfronts are shown in the video below.  The microfronts advance from the upper right to the lower left.  This propagation direction is between the downvalley direction and the downslope direction on the side of the valley with a steeper more extensive slope.

The passage of the microfront past a fixed point must be detected in terms of the abrupt change of wind direction indicated by the fog motion not the fog distribution.  The boundary between the foggy air and the less foggy air in the first example is not the microfront because some significant fog is found behind the microfront.  That is, the clearer air arrives some time after the microfront passage.  In addition, the circulation varies significantly along the micro front. Closer inspection of the first microfront indicates significant wind vertical directional shear that evidently stems from the greater wind direction shift at the surface compared to that at higher levels.  In the second image below, the edge of the fog is approximately aligned with the micro front.  This case is simpler than the first example.  These two cases are animated in the video.

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