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Fact File: Sea Mist

During spring and early summer we sometimes experience sea mist along the coast of Cornwall. Just half a mile inland there can be beautiful blue skies and sunshine first thing in the morning, whilst at sea level on the beach there is thick fog.

What Causes Sea Mist?

sea swimmer and sea mist at port isaac, cornwall

Sea swimming as the mist clears.

Sea mist is caused by the temperature difference between the land and the sea. This is most pronounced in spring and early summer if we get a sudden spell of very warm weather and easterly winds after a cold winter, as the land warms up much faster than the sea. It is an example of advection fog.  In the morning the sun heats the land and the warm, moist air above it is blown over the cool sea by the offshore easterly wind. Because the surface of the sea is still relatively cold, it cools the air just above it forcing it to condense and creating fog. As the morning progresses the sun usually burns the sea mist off quite quickly, sometimes leaving lingering fingers of fog in sheltered coves and inlets.

How Common is Sea Mist in Cornwall?

Sea mist is not as common here in Cornwall as it is on the East Coast of the UK, and is usually the result of exceptionally warm weather. It also tends not to last very long – in fact quite often it has dispersed by the time that most people enjoying a holiday here have finished their breakfast. For early risers though, watching the mist clear to reveal a beautiful blue sky and sunshine can be a lovely way to start the day, especially if you’re watching it from the water during an early morning sea swim.

 

So far this spring and summer we’ve had some glorious weather and some beautifully misty mornings, but sadly we’ve not been open and there have been no visitors in Cornwall to see it. Sea mist does still occur later into the summer though, so hopefully some of you will still get to start your days watching the mist burn off the sea to reveal a stunning day.