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SailingAlamancwhite1a1 Weather Weather Menu

READING THE SKY
Clouds consist of droplets of water (ice or snow) in suspension. The warmer the air the greater capacity to carry moisture. If the temperature falls or too much moisture is fed into a cloud, it sheds in the form of rain, hail or snow (i.e. precipitation).

Cirrus is feathery, either white or transparent, but can just obscure the sun.
The stratus family is like a fog and can be associated with drizzle. It often occurs in a warm front.
The nimbus family defines thick rain bearing cloud.
The cumulus family is puffy, sometimes harmless, but can develop into huge masses, bearing showers, rain or thunderstorms. Cumulus is typical for the back side of a low which has passed overhead.
In exceptional storm conditions nimbus and cumulus can rise bubbling up to 10-15,000 metres and more. These are definitely conditions to avoid if possible.

To supplement the forecast we can make our own observations:

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At Sunrise

If dawn breaks close to the horizon, fair weather is likely, but if the dawn breaks above a cloud bank it could be windy.

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A purple sky

Means bad weather, as does a red sunrise, with large clouds bringing rain.

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A rosey sky

At sunset means fair weather, but a very dark red or purple sky means rain.

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A yellow rising moon

Brings rain; a red moon brings winds. A new moon in the arms of the old moon means a storm.

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Halos

Around the sun or moon means rain. If the halo is open to one side that's the quarter the rain will come from. But a Corona (a small circle) around the suit or moon and growing smaller means fair weather.

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Rainbows

In the evening mean fair weather.

HIGH CLOUD (above 6000m)

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Cirrus (Ci)

Very high white feathery clouds (mares' tails) consisting of ice-particles, usually indicate wind aloft. If it thickens it indicates weather deterioration with the approach of a low. Watch the barometer. Depending on the intensity of the front, the weather will deteriorate within 12 to 24 hours.

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Cirrocumulus (Cc)

Mackerel sky. Rows of small white puffs in ripples, very high up sometimes forming banks. Thicker than Cirrus, it is harmless. Nevertheless, these clouds can foretell changeable weather.

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Cirrostratus (Cs)

A thin high milky veil, through which the sun can be seen, sometimes with a halo. Harmless until the cloud thickens, when it again can indicate an approaching depression arriving within 12 to 24 hours.

MEDIUM CLOUD (2000 to 6000m)

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Altocumulus (Ac)

A larger and thicker version of Cirrocumulus occurring in areas of high pressure or on the edges of warm zones. If the clouds develop vertically in the early hours of, or up to mid-morning, they foretell thunderstorms which will normally occur during the afternoon. Before the thunderstorms, the cloud will have disappeared.

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Altostratus (As)

Sheet-like grey cloud covering the entire horizon like a layer of medium level fog, through which the sun may sometimes still be seen, without halo. Following Cirrostratus, rain and an approaching front can be expected within one to three hours.

LOW CLOUD (below 2000m)

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Nimbostratus (Ns)

A mass of low, grey, rain-bearing cloud. Normally following Altostratus with the passing of a front. Steady rain will set in.

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Stratus (St)

Soft, grey, fog-like layer of cloud as low as 300 or even 150m. High contours of coast are often obscured by low Stratus. If dense, Stratus can produce drizzle and poor visibility, and will be found between warm and cold fronts.

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Stratocumulus (Sc)

Dense, lumpy grey cloud at 700-1500m. As it intensifies to form a solid grey layer across the sky, it will rain within one or two hours.

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Cumulus (Cu)

Typical fair weather cloud which forms as separate white puffs. It develops during the morning but leaves large areas of blue sky. It forms due to rising warm air over land and will disappear towards evening.
If it intensifies to massive clouds with dark undersides and does not disappear at night, the barometer will begin to fall and a change in weather will occur shortly.

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Cumulonimbus (Cb)

A much larger, towering, and more dramatic cloud than cumulus. It can rise to great heights with huge tops developing into irregular mountain like feathering peaks. It is associated with heavy rain and thundery squalls. The higher the cloud and its feathery peaks (up to 10000m), the stronger the squalls (can be up to force eight). After the depression this cloud will accompany the passage of the cold front. It may also be found with active troughs.