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You don't need a weatherman to know which way the wind blows.

- Bob Dylan

 

Wind & Weather

Weather affects us all, but none more than the sailor.  Every time he ventures onto the sea, he knows it is out there waiting for him.  The best he can do is try to understand his foe and prepare himself for the worst.

 

Basic Cloud Formations

Cirrus

Cumulonimbus

Cumulus

Stratus

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:

  

 Cloud Type

Appearance

Altitude

Cumulonimbus

Thunderheads

Near ground to above 50,000 feet

Cirrostratus

Thin, wispy, above thunderheads

Above 18,000 feet

Cirrus

Thin, often with "mare's tail"

Above 18,000 feet

Cirrocumulus

Small puffy clouds

Above 18,000 feet

Altostratus

Thin, uniform, sometimes with "wide wale corduroy" appearance

6,000 - 20,000 feet

Altocumulus

Medium-sized puffy clouds

6,000 - 20,000 feet

Stratocumulus

Broad and flat on the bottom, puffy on top

Below 6,000 feet

Cumulus

Puffy clouds

Below 6,000 feet

Stratus

Uniform, thick to thin layered clouds

Below 6,000 feet

 

 

Highs & Lows

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.

Standing with you back to the wind, extend your arms to 10 o'clock and 4 o'clock.  Your left arm will point to the low pressure area and you right arm will point to the high pressure area in the northern hemisphere.  (In the southern hemisphere, the high is to your left and the low is to your right.)

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.

Cold Fronts & Warm Fronts

 

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.

A backing wind means storms are nigh;

Veering wind will clear the skies.

Mackerel skies and mares' tails,

Mean high winds and full sails.

 

Squalls

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.

Clouds & Wind

Worsening weather - Wind backs counterclockwise in the northern hemisphere (clockwise in the southern hemisphere), and pressure drops. 

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.

Sound traveling far and wide

A stormy day will betide.

 

Barometric Pressure Changes

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.

Rate of Barometric Fall

A fall of .01 inch per hour is considered a low rate.

A fall of .03 inch per hour is considered a high rate.

A fall of .10 inch is possible; .20 inch has been recorded.

Barometer changes forecast 8-12 hours in the future.

Barometric Reading in the Middle Latitudes

29.60 inches is very low.

30.00 inches is average.

30.50 inches is high.

 

Hurricane Season in the Caribbean, Gulf of Mexico, and U.S. East Coast

June:  too soon

July:  stand by

August:  come it must

September:  remember

October:  all over

--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.

Rainbow to windward, foul fall the day;

Rainbow to leeward, damp runs away.

-- Old weather saying

 

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.

 

When halo rings the moon or sun,

Rain's approaching on the run.

-- Old weather saying

 

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

Force Number

Speed in knots

Description

0 0-0.9 Calm
1 1-3 Light air
2 4-6 Light breeze
3 7-10 Gentle breeze
4 11-16 Moderate breeze
5 17-21 Fresh breeze
6 22-27 Strong breeze
7 28-33 Near gale
8 34-40 Gale
9 41-47 Strong gale
10 48-55 Storm
11 56-63 Violent storm
12 64+ Hurricane

 

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.

 

 

 

Fog

Usually results in visibility less than 1100 yards (i.e. approximately 1/2 mile or 1000 meters)

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,

'Twill rain tomorrow, so 'tis said.

 

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