In short, the temperature of
the ocean water must be lower than the temperature
of the air moving over it for a fog bank to occur.
In other words, the water and the air can be any
temperature, as long as the water is
significantly cooler than the air.
To transport warmer air over cooler ocean water we
need wind. When winds are blowing in the right
direction to bring warmer air over cooler ocean
water, fog will start to form. They will
disappear when the difference in temperature
between the water and the air decreases. This
requires either the ocean surface to get warmer,
or the air to get colder.
We often see fog banks form along California’s
coast; it is because the ocean water along our coast
is very cold compared to the rest of the ocean.
This is why the fog banks that form at our coasts
are quite narrow – if you traveled in a boat out
to sea you would soon move past the fog bank into
clear skies. This is because during the summer
months, cold water up wells to the surface from
the bottom of the ocean along a narrow strip of
coastline. At this time of the year the wind
usually blows towards the California coast from
west to east, bringing with it a lot of
that has evaporated from other parts of the
Pacific Ocean. When this air approaches the cold
water at the California coast, the moisture in it
condenses into visible droplets, creating fog.
Since this wind is blowing from the ocean towards
the land, the fog is sometimes blown onto the
beach or even further inland, until the sun burns
This type of fog formation is sometimes called
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