Basic Cloud Formations

Clouds are defined by their general appearance and level in the atmosphere.

A prefix is frequently given to the cloud name to indicate the level of the atmosphere in which it resides.

Cirro is the prefix given to high clouds, those with bases above 20,000 feet.
Alto is the prefix given to mid-level clouds, those between 6,000 and 20,000 feet.
Nimbo added to the beginning or nimbus added to the end of a cloud name means the cloud is producing precipitation.

The system is by no means uniform. There is no term for low clouds, and there are some odd joinings, such as stratocumulus, which is a cloud with two different shapes.

So here's how some cloud types stack up:

Winds blow clockwise around a high pressure area in the northern hemisphere and veer outward.  (Winds rotate counterclockwise In the southern hemisphere.)

Winds blow counterclockwise around a low pressure area in the northern hemisphere and veer inward.  (Winds rotate clockwise in the southern hemisphere.)

The closer a high is to a low, the closer the isobars and more wind is generated.

In days past, sailors would use this simple technique to help guide them away from lows and toward highs where they had a better chance of encountering more pleasant weather conditions.  It also aided them in running away from hurricanes.

Both cold front and warm fronts bring with them rain, but the events leading up to the rain differ slightly.  The onset of each front is announced by different cloud formations.

Northern Hemisphere:  Wind shifts toward right (clockwise or veering) when either a warm or cold front passes.

Southern Hemisphere:  Wind shifts left (counterclockwise or backing) when either a warm or cold front passes.

 

Cold Front Cold air replaces warm air Moves rapidly, often signaled by towering cumulus clouds. Rain, strong winds, and thunderstorms. Wind veers clockwise as the front passes.

Warm Front Warm air replaces cold air. Moves slowly (1/2 speed of cold front). Lots of showery precipitation. If air is unstable, thunderstorms and strong winds are possible.

Stationary Front Air masses of equal pressure opposing each other. Doesn't move. Weather similar to warm front but less intense. Winds parallel the front.

Squalls have their own inherent characteristics, two of which are heavy rain and strong winds.

They are fast moving and usually short in duration.

When encountering a squall, it is often best to shorten sail in advance of its approach and to batten down the hatches.

Improving weather - Wind veers clockwise in the northern hemisphere (counterclockwise in the southern hemisphere), and pressure rises and stabilizes.

High and low clouds move in different directions:

Stand with your back to the movement of the lower clouds.

A change for the worse if the high clouds move left to right in the northern hemisphere.

A change for the better if the high clouds move right to left in the northern hemisphere.

A stormy day will betide.

A stationary barometer indicates that current weather conditions are likely to continue.

A high and steady or rising barometer indicates settled weather.

Lower than normal and steady or a falling barometer indicates unsettled weather.

A rapid rise or fall indicates that a strong wind is likely to blow and the weather is likely to change.

The speed of a storm's approach and its intensity will be indicated by the rate of barometric fall and its amount.

If the barometer falls without a change in weather, it's likely there is a violent storm a long way off.

First rise after a low,

Foretells a stronger blow.

--Old weather saying

Rainbows

A rainbow is created by the refraction of sunlight in drops of rain in the air.

The center of the bow is opposite the sun.

A rainbow in the morning is to the west of the observer, and it is likely the rain that created it will pass overhead.

A rainbow in the afternoon is to the east, and the rain is likely to be moving away.

Dew on the Deck

Dew in the morning indicates fine weather ahead.

Heavy dew and hot weather indicate continuing fine weather.

If there is no dew in the morning and the previous day was hot, rain is likely.

Wind Speed

Less than 1 knot – smoke rises vertically

1-3 knots – smoke drifts

4-6 knots – wind felt on face

7-10 knots – light flag extends from pole

11-16 knots – wind raises dust, cinders, loose paper, etc.

17-21 knots – flag waves and snaps briskly

22-27 knots – wind whistles in the rigging

28-33 knots – walking against wind is difficult

34-40 knots – wind impedes progress

When water is very cold and air is warm (e.g. spring mornings), wind speed at the mast head won't match wind speed at the water.

White caps will form with the wind speed reached 12 knots.

Beaufort Wind Scale

True Wind vs. Apparent Wind

The wind as it naturally blows is called the "true wind."

The wind you feel while sailing is referred to as the "apparent wind."

The apparent wind is not from the exact same direction as the true wind because of the wind generated by the forward motion of the boat.

The apparent wind is always slightly forward of the true wind when underway.

Land Breeze

A land breeze is a movement of air off the land onto the water that occurs after sunset as the air cools over the land, sinks, and flows off the land onto the warmer sea.

Sea Breeze

A sea breeze is a movement of air off the sea onto the land after sunrise as the air heats and rises over the land, pulling the air onto the land off of the cooler sea.

Radiation Fog

Over land at night.

Caused by the ground cooling the air below the dew point.

Usually not present when there are high winds.

Usually burns off with the morning sun.

Advection Fog

Caused when warm, moist air moves over cool land.

Can occur with heavy winds and in any season.

Usually persistent and prolonged.

Sunsets

Bright yellow - wind

Pale yellow - rain

Pink - Fair weather

If the sun goes pale to bed,