Why is fog hard to forecast?

Fog can disrupt our morning commutes or school runs, especially when freezing fog arrives as seen in Scotland this week. But why is it so hard to forecast?

Firstly, there are five different types of fog which form in slightly unique ways to each other. The primary source of each type is linked to temperature change occurring overnight, although some can take place in the day.

The trouble with predicting the arrival of fog is the extremely sensitive ingredients that go into its formation: Cloud cover, wind speed, temperatures, moisture levels, and daylight hours all play a part.

Winds need to be light enough to maintain moisture in the air but there is a sweet spot. If winds are too slight a ground dew will appear but if heavier winds arrive moisture will be strewn throughout the air maintaining too high a temperature.

Another key ingredient is the temperature change from day to night, meaning forecasters need to know the day’s maximum temperature in advance to predict fog.

With so many aspects behind fog, if just one is slightly inconsistent with what has been forecast days in advance, fog could either not appear at all, or form much denser than expected.

Learn more about how fog develops by watching our Weather Explained video below: