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Seamansh Seamansh ip ip Weather Weather Canadian Power & Sail Canadian Power & Sail Squadrons Squadrons

Seamanship Weather Canadian Power & Sail Squadrons

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Page 1: Seamanship Weather Canadian Power & Sail Squadrons

SeamansSeamanshiphip

WeatherWeatherCanadian Power & Canadian Power & Sail SquadronsSail Squadrons

Page 2: Seamanship Weather Canadian Power & Sail Squadrons

GeneralGeneralWeather conditions are of great Weather conditions are of great concern to all boaters. The greater your concern to all boaters. The greater your understanding of weather the more understanding of weather the more easily you can adapt to changes, both easily you can adapt to changes, both expected and unexpected. expected and unexpected.

Fundamentals of Weather and Global Fundamentals of Weather and Global Weather courses are offered to provide Weather courses are offered to provide boaters with a more complete study of boaters with a more complete study of meteorology.meteorology.

Page 3: Seamanship Weather Canadian Power & Sail Squadrons

Weather ForecastsWeather ForecastsWeather results from four general Weather results from four general characteristics of the atmosphere.characteristics of the atmosphere.

- Pressure- Pressure

- Temperature- Temperature

- Humidity- Humidity

- Movement - Movement

Page 4: Seamanship Weather Canadian Power & Sail Squadrons

Forecasts are based on measurements of Forecasts are based on measurements of these characteristics, taken at many places these characteristics, taken at many places simultaneously and collated to create a simultaneously and collated to create a general forecast for the region.general forecast for the region.

The most important feature of any forecast is The most important feature of any forecast is its time and date of issue; if it is more than 15 its time and date of issue; if it is more than 15 hours old it is out of date!hours old it is out of date!

Accept that a general forecast for a large Accept that a general forecast for a large region, i.e. The Strait of Georgia, is rarely region, i.e. The Strait of Georgia, is rarely accurate for every place within it. Issues such accurate for every place within it. Issues such as time lags between data collection and as time lags between data collection and forecast distribution and local conditions will forecast distribution and local conditions will affect accuracy.affect accuracy.

Page 5: Seamanship Weather Canadian Power & Sail Squadrons

Make an effort to learn the local effects Make an effort to learn the local effects of your boating area. Publications are of your boating area. Publications are available that can help you in this regard:available that can help you in this regard:

- Marine Weather Hazards Manual- Marine Weather Hazards Manual

- The Wind Came all Ways- The Wind Came all Ways

Both are Environment Canada Both are Environment Canada publications written by marine weather publications written by marine weather forecaster Owen Lange and are available forecaster Owen Lange and are available locally at the chart shop on Church locally at the chart shop on Church Street.Street.

Page 6: Seamanship Weather Canadian Power & Sail Squadrons

Adjust the forecast to meet these local Adjust the forecast to meet these local effects if necessary but listen to the effects if necessary but listen to the marine weather forecast before casting marine weather forecast before casting off and get the updates as they are off and get the updates as they are made available. Supplement the made available. Supplement the predictions with your own observations predictions with your own observations of weather conditions. of weather conditions.

Be aware of the likelihood of changes in Be aware of the likelihood of changes in the wind, or of the development of the wind, or of the development of storms, rough seas or reduced visibility.storms, rough seas or reduced visibility.

Page 7: Seamanship Weather Canadian Power & Sail Squadrons

Atmospheric Conditions That Cause Atmospheric Conditions That Cause WeatherWeather

PressurePressure Air pressure is the result of the weight of all Air pressure is the result of the weight of all

the air above the earth’s surface.the air above the earth’s surface. It plays a major role in the generation of wind.It plays a major role in the generation of wind. Pressure decreases with altitude.Pressure decreases with altitude. Measured with a barometer, units vary, can Measured with a barometer, units vary, can

be inches of mercury, lbs/sq. in., millibars, or be inches of mercury, lbs/sq. in., millibars, or kilopascals (Canada).kilopascals (Canada).

Page 8: Seamanship Weather Canadian Power & Sail Squadrons

The actual pressure is of less The actual pressure is of less importance than the rate of change importance than the rate of change (pressure tendency).(pressure tendency).

Observing pressure tendency and Observing pressure tendency and changes in wind direction over a changes in wind direction over a period of a few hours can indicate period of a few hours can indicate much about approaching weather.much about approaching weather.

It doesn’t hurt to have a marine It doesn’t hurt to have a marine barometer on board.barometer on board.

Page 9: Seamanship Weather Canadian Power & Sail Squadrons

TemperatureTemperature

The earth absorbs energy from the The earth absorbs energy from the sun and radiates this heat back into sun and radiates this heat back into the atmosphere resulting in a the atmosphere resulting in a decrease in temperature with decrease in temperature with altitude. altitude.

The earth is heated unevenly due to The earth is heated unevenly due to land/water/ice cover, and shade land/water/ice cover, and shade caused by objects such as buildings, caused by objects such as buildings, trees, mountains or cloud.trees, mountains or cloud.

Page 10: Seamanship Weather Canadian Power & Sail Squadrons

This unequal heating causes This unequal heating causes differences in air temperature from differences in air temperature from place to place over the earth’s surface.place to place over the earth’s surface.

Heated air expands and rises. As it Heated air expands and rises. As it rises, it cools and becomes more rises, it cools and becomes more dense. Once the rising air reaches the dense. Once the rising air reaches the same density as its surroundings the same density as its surroundings the ascent will stop.ascent will stop.

Although changes in temperature are Although changes in temperature are easily detected without instruments, a easily detected without instruments, a thermometer is a useful device to thermometer is a useful device to carry on board.carry on board.

Page 11: Seamanship Weather Canadian Power & Sail Squadrons
Page 12: Seamanship Weather Canadian Power & Sail Squadrons

HumidityHumidity

Moisture content of the air.Moisture content of the air. Major factor in adverse weather.Major factor in adverse weather. The warmer the air, the more The warmer the air, the more

moisture it can hold.moisture it can hold. Saturation occurs when the water Saturation occurs when the water

vapour content reaches its maximum vapour content reaches its maximum for a given air mass.for a given air mass.

Page 13: Seamanship Weather Canadian Power & Sail Squadrons

Relative humidity is tRelative humidity is the actual he actual amount of water vapor in the air amount of water vapor in the air compared with the maximum it could compared with the maximum it could hold at that temperature, expressed hold at that temperature, expressed as a percentage.as a percentage.

Remember that the amount of Remember that the amount of moisture that the atmosphere can moisture that the atmosphere can hold is dependant on the temperature hold is dependant on the temperature and if cooled sufficiently, the air will and if cooled sufficiently, the air will become saturated.become saturated.

Page 14: Seamanship Weather Canadian Power & Sail Squadrons

The temperature to which the air must be The temperature to which the air must be cooled to reach saturation is called the dew cooled to reach saturation is called the dew point.point.

When the temperature and dew point are When the temperature and dew point are the same the relative humidity will be the same the relative humidity will be 100%.100%.

Further cooling will result in condensation Further cooling will result in condensation which will cause the formation of fog, which will cause the formation of fog, clouds or dew.clouds or dew.

One can normally detect the level of One can normally detect the level of humidity without the aid of instruments but humidity without the aid of instruments but such devices are relatively inexpensive and such devices are relatively inexpensive and readily available.readily available.

Page 15: Seamanship Weather Canadian Power & Sail Squadrons

Atmospheric MotionAtmospheric Motion

Cloud FormationCloud Formation In addition to the movement of air In addition to the movement of air

caused by changes in pressure, the caused by changes in pressure, the daily cycle of solar heating and daily cycle of solar heating and cooling results in almost continual cooling results in almost continual motion of the atmosphere. motion of the atmosphere.

Air warmed by the ground which has Air warmed by the ground which has been heated by the sun, will rise, been heated by the sun, will rise, carrying its moisture content aloft. carrying its moisture content aloft.

Page 16: Seamanship Weather Canadian Power & Sail Squadrons

As the air rises, it cools until the dew As the air rises, it cools until the dew point is reached. At this point the point is reached. At this point the moisture condenses into water moisture condenses into water droplets and clouds are formed.droplets and clouds are formed.

Page 17: Seamanship Weather Canadian Power & Sail Squadrons

Cloud FormationCloud Formation

Page 18: Seamanship Weather Canadian Power & Sail Squadrons

Surface Winds (Related to Cloud Formation)Surface Winds (Related to Cloud Formation)

Air rising from the surface will draw air from Air rising from the surface will draw air from surrounding areas.surrounding areas.

Land and Sea Breezes (Local Winds)Land and Sea Breezes (Local Winds) As land masses are heated by the late As land masses are heated by the late

morning sun the air above is warmed and morning sun the air above is warmed and rises, (thermal low) drawing in the cooler air rises, (thermal low) drawing in the cooler air from the sea. from the sea.

A gentle on-shore breeze results which may A gentle on-shore breeze results which may extend a mile or two out to sea and will be extend a mile or two out to sea and will be easily perceptible providing no overriding easily perceptible providing no overriding gradient wind is present.gradient wind is present.

Page 19: Seamanship Weather Canadian Power & Sail Squadrons

Sea BreezeSea Breeze

Page 20: Seamanship Weather Canadian Power & Sail Squadrons

In the evening, the land cools rapidly In the evening, the land cools rapidly to a temperature below that of the to a temperature below that of the water, the cool air sinks and flows water, the cool air sinks and flows away from the land to replace the away from the land to replace the warmer air rising off the water. warmer air rising off the water.

In calm weather, these off-shore In calm weather, these off-shore breezes may be all that is available breezes may be all that is available to serve the sailor, and many races to serve the sailor, and many races have been won by taking advantage have been won by taking advantage of them.of them.

Page 21: Seamanship Weather Canadian Power & Sail Squadrons

Land BreezeLand Breeze

Page 22: Seamanship Weather Canadian Power & Sail Squadrons

Gradient WindsGradient Winds

Weather systems around the world are Weather systems around the world are characterised by well-defined centres of characterised by well-defined centres of low pressure (LOWS), where pressure is low pressure (LOWS), where pressure is lower than in the surrounding region, lower than in the surrounding region, and areas of high pressure (HIGHS). and areas of high pressure (HIGHS).

Air tends to blow from regions of higher Air tends to blow from regions of higher pressure to those of lower pressurepressure to those of lower pressure, and , and the deeper the low, the stronger the the deeper the low, the stronger the winds. These are gradient winds.winds. These are gradient winds.

Page 23: Seamanship Weather Canadian Power & Sail Squadrons

Surface Weather MapSurface Weather Map

Page 24: Seamanship Weather Canadian Power & Sail Squadrons

Centres of Low PressureCentres of Low Pressure

Weather systems tend to move across North Weather systems tend to move across North America in a west to east direction. This America in a west to east direction. This results in constantly changing pressure at any results in constantly changing pressure at any given spot. given spot.

In the northern hemisphere, In the northern hemisphere, air moves around air moves around a LOW in a counter clockwise direction a LOW in a counter clockwise direction and and slightly toward the centre. slightly toward the centre.

The circles around the lows and highs on a The circles around the lows and highs on a weather map are called isobars, or lines of weather map are called isobars, or lines of equal pressure. The closer together isobars equal pressure. The closer together isobars are, the stronger the winds. are, the stronger the winds.

Air moves clockwise around a HIGH Air moves clockwise around a HIGH and and slightly away from the centre (Northern slightly away from the centre (Northern Hemisphere).Hemisphere).

Page 25: Seamanship Weather Canadian Power & Sail Squadrons

Buys-Ballots LawBuys-Ballots Law Typically a centre of low pressure will Typically a centre of low pressure will

form at the interface between two form at the interface between two masses of air differing in temperature masses of air differing in temperature and/or moisture content. On the and/or moisture content. On the following weather map, the low is at following weather map, the low is at the juncture of a warm and a cold front.the juncture of a warm and a cold front.

You can use Buys-Ballots law to locate You can use Buys-Ballots law to locate the centre of low pressure:the centre of low pressure:

““Stand with your back to the wind, Stand with your back to the wind, and the low pressure centre will lie and the low pressure centre will lie to your left and slightly ahead of to your left and slightly ahead of youyou.”.”

Page 26: Seamanship Weather Canadian Power & Sail Squadrons

Thanks to the Practical Encyclopaedia of Boating

Page 27: Seamanship Weather Canadian Power & Sail Squadrons

Buys-Ballots law only works in the Buys-Ballots law only works in the northern hemisphere.northern hemisphere.

Christophorus Henricus Diedericus Christophorus Henricus Diedericus Buys BallotBuys Ballot (also Christoph Heinrich (also Christoph Heinrich Diedrich Buys Ballot) (October 10 1817 – Diedrich Buys Ballot) (October 10 1817 – February 3, 1890) was a Dutch chemist February 3, 1890) was a Dutch chemist and meteorologist after whom Buys Ballots and meteorologist after whom Buys Ballots Law was named. William Ferrel, an Law was named. William Ferrel, an American, actually discovered the American, actually discovered the phenomena slightly earlier. phenomena slightly earlier.

Page 28: Seamanship Weather Canadian Power & Sail Squadrons

FrontsFronts A front is the boundary between two A front is the boundary between two

adjacent air masses differing mainly in adjacent air masses differing mainly in temperature. temperature.

Because the whole system is in constant Because the whole system is in constant motion, one air mass will move against the motion, one air mass will move against the other. other.

If a mass of warmer air is over taking a If a mass of warmer air is over taking a stationary mass of cooler air, the front is stationary mass of cooler air, the front is called a called a warm frontwarm front. .

A mass of cooler air is pushing under a mass A mass of cooler air is pushing under a mass of warmer air is called a of warmer air is called a cold frontcold front..

Page 29: Seamanship Weather Canadian Power & Sail Squadrons

On a weather map cold fronts are On a weather map cold fronts are distinguished by spikes, warm fronts distinguished by spikes, warm fronts by half circles. On a coloured map by half circles. On a coloured map cold fronts are blue, warm fronts are cold fronts are blue, warm fronts are red.red.

Both front types are characterised Both front types are characterised by cloud cover, precipitation, and by cloud cover, precipitation, and wind shifts but their movements wind shifts but their movements affect the weather differently.affect the weather differently.

Page 30: Seamanship Weather Canadian Power & Sail Squadrons
Page 31: Seamanship Weather Canadian Power & Sail Squadrons

Cold fronts move faster than warm Cold fronts move faster than warm fronts and can catch up, this is an fronts and can catch up, this is an occlusion. occlusion. The warm air will be The warm air will be lifted clear of the ground creating a lifted clear of the ground creating a trough of warm air aloft or a trough of warm air aloft or a TROWAL.TROWAL.

Trowals produce weather much like Trowals produce weather much like a warm front and are shown on a a warm front and are shown on a weather map by symbols that look weather map by symbols that look like backwards sevens.like backwards sevens.

Page 32: Seamanship Weather Canadian Power & Sail Squadrons
Page 33: Seamanship Weather Canadian Power & Sail Squadrons

Warm FrontWarm Front

Warm fronts occur as cold air retreats, the Warm fronts occur as cold air retreats, the advancing warm air rises above the cold air advancing warm air rises above the cold air which is more dense. which is more dense.

Stratus or other layer type clouds form as the Stratus or other layer type clouds form as the warm air rises and eventually cools to the dew warm air rises and eventually cools to the dew point. point.

Cirrus clouds called mare’s tails may be seen Cirrus clouds called mare’s tails may be seen up to 540nm ahead of the surface position of up to 540nm ahead of the surface position of the front. the front.

Warm fronts are much slower than cold Warm fronts are much slower than cold fronts. Precipitation may occur and can fronts. Precipitation may occur and can extend out to 200 to 300nm ahead of the extend out to 200 to 300nm ahead of the surface frontal position.surface frontal position.

Page 34: Seamanship Weather Canadian Power & Sail Squadrons

Warm FrontWarm Front

Page 35: Seamanship Weather Canadian Power & Sail Squadrons

Cold FrontCold Front A mass of colder air moving against a A mass of colder air moving against a

mass of warmer air will force the mass of warmer air will force the warmer air to rise abruptly. warmer air to rise abruptly.

Cumulus or even cumulonimbus clouds Cumulus or even cumulonimbus clouds will form, producing showers or will form, producing showers or thunderstorms. thunderstorms.

The precipitation and storms are The precipitation and storms are usually more severe with air of greater usually more severe with air of greater moisture content.moisture content.

Conditions following the passage of a Conditions following the passage of a cold front are frequently turbulent with cold front are frequently turbulent with gusty winds followed by clearing skies.gusty winds followed by clearing skies.

Page 36: Seamanship Weather Canadian Power & Sail Squadrons

Cold FrontCold Front

Page 37: Seamanship Weather Canadian Power & Sail Squadrons

ForecastingForecasting

Clues to Watch For:Clues to Watch For: Clouds alone do not necessarily Clouds alone do not necessarily

reveal future weather. Changing reveal future weather. Changing cloud patterns along with other cloud patterns along with other indicators such as barometric, indicators such as barometric, temperature and humidity trends, temperature and humidity trends, and changes in wind direction and and changes in wind direction and speed can serve as a basis for speed can serve as a basis for reliable forecasts.reliable forecasts.

Page 38: Seamanship Weather Canadian Power & Sail Squadrons

The three most reliable clues regarding The three most reliable clues regarding the kind of weather in store are:the kind of weather in store are:

1.1. The direction of the windThe direction of the wind2.2. The rate and direction of pressure The rate and direction of pressure

changeschanges3.3. The nature of the cloudsThe nature of the clouds

Weather Patterns should be learned Weather Patterns should be learned thoroughly as a practical guide to the thoroughly as a practical guide to the more serious hazards one probably will more serious hazards one probably will face. The hazards of weather are greatly face. The hazards of weather are greatly reduced by adequate preparation.reduced by adequate preparation.

Page 39: Seamanship Weather Canadian Power & Sail Squadrons

Warm Front PatternWarm Front Pattern Barometric pressure falling. The more Barometric pressure falling. The more

rapid the fall, the more severe or more rapid the fall, the more severe or more rapid is the approach of bad weather.rapid is the approach of bad weather.

Winds southerly, southeasterly, or Winds southerly, southeasterly, or easterly.easterly.

General and increasing cloud cover, General and increasing cloud cover, usually in the sequence: cirrus (mare’s usually in the sequence: cirrus (mare’s tails), altostratus (milky sun), and tails), altostratus (milky sun), and stratus (low layered, featureless cloud stratus (low layered, featureless cloud cover).cover).

The presence of all three of the above The presence of all three of the above signs indicate deteriorating weather. signs indicate deteriorating weather.

Page 40: Seamanship Weather Canadian Power & Sail Squadrons

Cirrus

Page 41: Seamanship Weather Canadian Power & Sail Squadrons

Altostratus

Page 42: Seamanship Weather Canadian Power & Sail Squadrons

Stratus

Page 43: Seamanship Weather Canadian Power & Sail Squadrons

Cold Front PatternCold Front Pattern

Gives little indication of its approach.Gives little indication of its approach. Watch for large puffy clouds, cumulus Watch for large puffy clouds, cumulus

or cumulonimbus, on the western or cumulonimbus, on the western horizon indicating a moist and rapidly horizon indicating a moist and rapidly moving front.moving front.

Winds that shift from southeasterly Winds that shift from southeasterly through south and southwest may through south and southwest may change further to westerly or change further to westerly or northwesterly with possible squalls.northwesterly with possible squalls.

Page 44: Seamanship Weather Canadian Power & Sail Squadrons

A shift to strong and gusty winds from A shift to strong and gusty winds from west to northwest indicate a cold frontal west to northwest indicate a cold frontal passage.passage.

The most dramatic wind shifts take place The most dramatic wind shifts take place with the cold frontal passage, winds may with the cold frontal passage, winds may veer 90veer 90oo..

Winds following a cold front frequently Winds following a cold front frequently remain gusty. If strong winds precede the remain gusty. If strong winds precede the wind shifts, then strong, usually wind shifts, then strong, usually northwesterly, winds will follow as the northwesterly, winds will follow as the weather clears. weather clears.

The pressure will rise with the cold The pressure will rise with the cold frontal passage.frontal passage.

Page 45: Seamanship Weather Canadian Power & Sail Squadrons
Page 46: Seamanship Weather Canadian Power & Sail Squadrons

Cumulus Cloud (Towering Cumulus)Thanks to atmospheric-violence.com

Page 47: Seamanship Weather Canadian Power & Sail Squadrons

Signs of Improving Weather Signs of Improving Weather ConditionsConditions

Barometer steady or risingBarometer steady or rising Wind shifting from easterly through north Wind shifting from easterly through north

to northwesterly (backing), or from to northwesterly (backing), or from southeasterly through south to southeasterly through south to southwesterly (veering); i.e., a shift southwesterly (veering); i.e., a shift towards westerly winds in either case.towards westerly winds in either case.

Backing means a wind shift in a counter Backing means a wind shift in a counter clockwise direction. Veering means a wind clockwise direction. Veering means a wind shift in a clockwise direction.shift in a clockwise direction.

Page 48: Seamanship Weather Canadian Power & Sail Squadrons

FogFog A reduction in visibility caused by A reduction in visibility caused by

suspended water droplets in the suspended water droplets in the atmosphere. Fog is cloud at ground atmosphere. Fog is cloud at ground level and formed by the same level and formed by the same principles.principles.

Water vapour must be present and Water vapour must be present and cooled to its dew point in order for cooled to its dew point in order for fog to form. The various types of fog to form. The various types of fogs are named according to the fogs are named according to the processes involved in causing the processes involved in causing the water vapour to condense.water vapour to condense.

Page 49: Seamanship Weather Canadian Power & Sail Squadrons

Radiation FogRadiation Fog Forms at night under clear skies as the Forms at night under clear skies as the

earths surface cools rapidly after sunset. earths surface cools rapidly after sunset. Common under a ridge of high pressure Common under a ridge of high pressure in the fall.in the fall.

Requires light winds, sufficient moisture Requires light winds, sufficient moisture and enough cooling for the air to reach and enough cooling for the air to reach saturation. If the winds are calm, dew saturation. If the winds are calm, dew will form but not fog.will form but not fog.

Radiation fog will dissipate as the sun Radiation fog will dissipate as the sun warms the ground in the morning.warms the ground in the morning.

As a general rule, the earlier fog forms As a general rule, the earlier fog forms the later it will dissipate. the later it will dissipate.

Page 50: Seamanship Weather Canadian Power & Sail Squadrons

Radiation Fog

Page 51: Seamanship Weather Canadian Power & Sail Squadrons

Advection Fog or Sea FogAdvection Fog or Sea Fog Advection implies the horizontal Advection implies the horizontal

movement of air over the earth’s movement of air over the earth’s surface.surface.

Sea fog occurs most frequently over the Sea fog occurs most frequently over the northeast and west coasts of North northeast and west coasts of North America.America.

Caused when moist air moves over a Caused when moist air moves over a colder surface colder surface causing condensation, causing condensation, this is the most common type of this is the most common type of advection fog.advection fog.

A change in wind direction is required to A change in wind direction is required to dissipate this type of fog. dissipate this type of fog.

Page 52: Seamanship Weather Canadian Power & Sail Squadrons

Sea Fog at Robin Hood’s Bay (Yorkshire)Photo by Magda Indigo

Page 53: Seamanship Weather Canadian Power & Sail Squadrons

A second type of advection fog occurs A second type of advection fog occurs when very cold air flows over a warm when very cold air flows over a warm surface, usually water.surface, usually water.

Water vapour that rises from the Water vapour that rises from the water’s surface immediately water’s surface immediately condenses in the cold air and gives condenses in the cold air and gives the impression of smoke or steam, the impression of smoke or steam, hence the name Arctic Sea Smoke.hence the name Arctic Sea Smoke.

Usually occurs over waters close to a Usually occurs over waters close to a land surface, in our area we see Sea land surface, in our area we see Sea Smoke during Arctic outflow Smoke during Arctic outflow conditions over the Strait of Georgia.conditions over the Strait of Georgia.

Page 54: Seamanship Weather Canadian Power & Sail Squadrons
Page 55: Seamanship Weather Canadian Power & Sail Squadrons

Frontal Fog or Warm Front FogFrontal Fog or Warm Front Fog

Continuous rain falling ahead of a Continuous rain falling ahead of a warm front will evaporate into the warm front will evaporate into the cooler air below.cooler air below.

The cooler air may already be near The cooler air may already be near saturation and the additional water saturation and the additional water vapour will cause fog to form.vapour will cause fog to form.

This type of fog will not dissipate This type of fog will not dissipate until the front passes through.until the front passes through.

Page 56: Seamanship Weather Canadian Power & Sail Squadrons

Frontal Fog

Page 57: Seamanship Weather Canadian Power & Sail Squadrons

EndEnd