Rare weather phenomenon: Cascading advection fog mimicking orographic fog over the cliffs of Broadstairs

As someone captivated by liminal moments, the interplay between nature and weather is something that always piques my curiosity, so witnessing a unique phenomenon unfold over the cliffs of the Isle of Thanet was nothing short of extraordinary. On Saturday 11th Jan ’25, we’d had a really a cold, subzero day and fog started to form in the afternoon, but it was patchy and as I drove around the coast, I could see it was over land and it was strangely clear over the sea. I decided to grab my drone and take to the air and I was utterly blown away by the thin layer of fog making it feel like night was arriving an hour early, was mainly over land and creating a breathtaking display of fog cascading off the cliffs of Broadstairs onto the sea, mimicking the effect of orographic fog typically seen in mountainous regions. Moments like this remind me of the beauty of liminal spaces, living on this peninsula of wild edges and island of old, where land meets sea, day meets night, hot meets cold and the alchemy of it all created something truly spectacular.

And of course I got super curious about what I’d witnessed and did a deep dive trying to identify it and in the process realised that it was actually something really quiet unique because of a line up of a lot of conditions!

But before we dive into that, let’s just drift away and soak in some of the scenes from the sky.

What is orographic fog?

Orographic fog usually forms when moist air is forced to rise over elevated terrain, such as mountains or steep hills. As the air ascends, it cools and condenses into fog, often draping itself over the peaks or flowing down valleys like a waterfall of clouds. I have seen it a few times in Iceland and Norway, but here in Broadstairs, there are no mountains, just gently sloping terrain and dramatic coastal cliffs. However, with the gentle wind coming from the north/north-east, I know there is a slight incline in the elevation, the north coast that the air hit first being almost at sea level, rising towards Broadstairs by maybe 20-30m where the cliffs then sharply fall to sea level. So although this wasn’t a traditional set up for orographic fog, it was looking a little like it……my quest for answers continued.

The phenomenon in Broadstairs

On this particular afternoon, the fog began gathering inland before rising over land towards the cliffs and spilling over onto the sea below. From the ground, the movement of the fog was mesmerising, but it was only after flying my drone that I could truly appreciate the scale and beauty of what was unfolding. The drone revealed fog pooling over the land and then cascading like a soft, ethereal waterfall off the cliffs into the sea. These moments, so fleeting and magical, awaken something deep within me. It’s in these wild edges, these liminal spaces, that I feel most alive and connected to nature.

Why did this happen?

Understanding Advection Fog

Advection fog occurs when moist air moves horizontally over a cooler surface, causing the air to cool and condense into fog. This process is common in coastal regions, where warm, moist air from the sea drifts over colder land or water. In Broadstairs, the interaction between the cold land and the gentle north/northeast wind carrying moist air from the North Sea likely created a perfect environment for advection fog to form. Unlike orographic fog, which relies on significant elevation changes, advection fog spreads across the landscape, creating a blanket-like effect. However, in this case, the slight elevation of the cliffs added a dynamic twist, causing the fog to cascade downward like a waterfall onto the sea.

While it wasn’t orographic fog in the strictest sense, the principles behind its formation were strikingly similar. Here’s what likely happened:

1. Marine and land air interaction: The gentle wind carried moist air from the sea, which cooled rapidly as it traveled over the cold, subzero land of Thanet.
2. Temperature inversion: Prolonged cold weather likely created a temperature inversion, where cold air was trapped below a layer of warmer air, enhancing fog formation.
3. Local geography & cliff dynamics: As the air travelled north-to-south over Thanet, the slight elevation from an almost sea level north side, to the cliffs of 20-30m on the south of Thanet, forced the air to rise, causing additional cooling and condensation. Gravity then drew the denser fog down the cliffs, creating the cascading waterfall effect.

A unique and localised event

Unlike traditional orographic fog, which requires significant elevation changes, this phenomenon was shaped by the unique geography and conditions of the Isle of Thanet. The change in elevation as the warm, moist air arriving on the north coast, travelled south and gained elevation after the cold, dry land. Then the cliffs provided a wild edge for the fog to the cascade like a waterfall onto the surface of the sea. Having googled around, I found it difficult to find any examples like this one – perhaps I’ve not picked up on a phenomenon that caused it, or perhaps my curiosity led me to capture and analyse a spectacle that’s rarely observed or documented in coastal regions like this.

Why you may not find similar examples

This type of event likely requires a precise combination of weather conditions: prolonged cold temperatures, gentle but steady wind from the sea, bringing warmer, moist air, an incline of land that has been frozen for days resulting in a cold, dry surface and the presence of coastal cliffs. These factors make it a rare occurrence, and the images captured during this event may serve as valuable documentation for other folk looking to research and understand something they’ve witnessed.

Witnessing nature’s magick

Standing on the beach, where the earth meets the sea, watching the glow of the winter sun disappear below this band of fog over the land and watching this phenomenon unfold was an unforgettable reminder of nature’s ability to surprise and enchant us. These moments feel like invitations from the earth to pause, to notice, and to connect. It’s in chasing light and wild edges like this that I feel most aligned with my purpose, immersed in nature, alive with curiosity, and in awe of the world around me. If you’ve witnessed similar fog formations or have insights into this rare event, I’d love to hear from you. Share your thoughts the comments below!