I love fog. Fog is very important for my photography, as it creates the atmosphere and the mystery I look for with my images.

As you can imagine, being able to predict (or at least have some degree of confidence) where and when fog happens can make a big difference. That’s why I always keep an eye on some key numbers that are a good indicator of possible mist.

I use an app called Clear Outside. It’s not a good one, it’s old and hasn’t been updated in years, but I love how simple it is. I can see everything I need in one quick glimpse, with no distractions.

What I look for is:

Wind: as little wind as possible, ideally no wind at all.
Rain can create its own fog, but most of the time it will leave you with images that look like they were taken on a cloudy day. Only that you got wet to make them.
Humidity: has it rained lately? is the ground wet? are there lakes nearby? Here where I live, fog won’t happen if humidity is below 90%.
Temperature: a cold night followed by a warm day can fill the air with all that humidity present on the ground.
Dew point: the closer to the actual temperature, the better. It is when these two values are the same that fog appears to be the thicker, at least in my experience.
Topology: valleys are more prone to fog, as they “trap” that humidity.

This is not an exact science, quite the opposite: predicting fog is really hard. But with the right numbers, and some knowledge about the location, you can have a rough idea of what to expect. And maybe have your camera bag ready to go, just in case.