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Little Falmouth Yacht Yard

Flushing, Falmouth

Cornwall, TR11 5TJ

Knowing your clouds

Boat repair Falmouth

Clouds are a really important part of boating, whether you are just planning a gentle morning sail or a world cruise. Here is our quick guide on how to spot them and what to expect. There are over 100 types of clouds but they can be grouped into 10 basic types.

Cumulus - Low-level, lie below 6,500 feet (1,981 m). Round and puffy on top and nicknamed the "fair weather clouds". They appear in the late morning, grow, and then disappear toward evening.

Stratus - Low-level, lie below 6,500 feet (1,981 m). Stratus clouds hang low in the sky as a flat, dull, layer of greyish cloud a bit like fog but on the horizon. Seen on dreary, overcast days and are associated with light mist or drizzle.

Stratocumulus - Low-level, lie below 6,500 feet (1,981 m). Low, puffy, greyish or whitish clouds that occur in patches with blue sky visible in between.

Altocumulus - Middle clouds, form between 6,500 and 20,000 feet (1981–6,096 m). Nicknames include "sheep backs" and "mackerel skies." Spotted on warm and humid mornings, especially during summer, thunderstorms to come later in the day. They also signal the beginning of cooler temperatures.

Nimbostratus - Middle clouds, form between 6,500 and 20,000 feet (1981–6,096 m). Cover the sky in a dark grey layer and thick enough to blot out the sun. It is a typical rain cloud. You'll see them whenever steady rain or snow is falling or is forecast over a widespread area.

Altostratus - Middle clouds, form between 6,500 and 20,000 feet (1981–6,096 m). Appear as grey or bluish-grey sheets of cloud in some or all of the sky. You can usually still see the sun faintly behind them, but not enough light shines through to cast shadows on the ground. Form ahead of a warm or occluded front and at a cold front they mix with cumulus.

Cirrus - High-level, form above 20,000 feet (6,096 m) Thin, white, wispy strands of clouds that streak across the sky, made up of tiny ice crystals. Normally occurs in fair weather but also can indicate storms may be coming. Nickname "Mares' tails".

Cirrocumulus - High-level, form above 20,000 feet (6,096 m). Small, white patches of clouds often in rows and are made of ice crystals. Rare and fairly short-lived, you'll see them in winter or when it's cold but fair.

Cirrostratus - High-level, form above 20,000 feet (6,096 m). Transparent, whitish clouds that nearly cover all of the sky. Show that there is a large amount of moisture in the upper atmosphere. They're also generally associated with future warm fronts.

Cumulonimbus - Tower across the low, middle, and upper atmosphere. The upper portion resembles a cauliflower and their bottoms are often hazy and dark. Thunderstorm clouds, so if you see one you can be sure there's a nearby risk of severe weather, short but heavy periods of rainfall and hail.

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