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International Bareboat Skipper > Meteorology, Short Passages & Heavy Weather > Flashcards

Meteorology, Short Passages & Heavy Weather Flashcards

1
Q

Meteorology

A
  • The study of weather, which is caused by the movement or transfer of energy occurring with the movementof air in the atmosphere.
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2
Q

What information is contained in a marine weather forecast?

A
  • Wind speed, direction and strength
  • Visibility
  • Temperature and sun strength
  • Wave height
  • Rain
  • Fog
  • Mist
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3
Q

What is an “Air Mass”?

A
  • An air mass is a large volume of air in the atmosphere that is mostly uniform in temperature and moisture.
  • An air mass can extend thousands of kilometers across the surface of the Earth and can reach from ground level to the stratosphere - 16 kilometers (10 miles)
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4
Q

What are the four categories of air masses?

A
  • Arctic air masses form in the arctic region and are very cold
  • Tropical air masses form in low-latitude areas and are moderately warm
  • Polar air masses take shape in high-latitude regions are are cold
  • Equatorial air masses develop near the Equator and are warm
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5
Q

Maritime air mass

A
  • Maritime air masses form over the water and are humid
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6
Q

Continental air mass

A
  • Continental air masses form over land and are dry
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7
Q

Coriolis Effect

A
  • This is created by the rotation of the Earth. It is what causes the circular movement of weather systems. As the Earth rotates on its axis, the surface will be moving at different rates.
  • Due to the earths rotation, low pressure systems in the Northern Hemisphere rotate in a counter clockwise direction and in a clockwise direction in the Southern Hemisphere.
  • High pressure systems in the Northern Hemisphere rotate in a clockwise direction and in a counter clokwise direction in the Southern Hemisphere.
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8
Q

Low Pressure System

A
  • A low pressure system has lower pressure at its center than the areas around it.
  • Winds blow towards the low pressure, and the air rises in the atmosphere where they meet.
  • As the air rises, the water vapor within it condenses forming clouds and often precipitation too.
  • Because of the coriolis effect winds of a low pressure system swirl counterclockwise north of the equator and clockwise south of the equator.
  • On a weather map a low pressure system is labeled with a red L
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9
Q

High Pressure System

A
  • A high pressure system has higher pressure at its center than the areas around it. Wind blows away from high pressure.
  • Winds swirl clockwise north of the equator and counterclockwise south of the equator.
  • On a weather map the location of a high pressure system is labeled with a blue H.
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10
Q

What are signs of weather change?

A
  • Cloud formation
  • Shift in wind direction and speed
  • Sudden change in atmospheric pressure
  • Changes in visibility
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11
Q

What is the normal barometric pressure?

A
  • 1013.25 mbar (101.325 kPa)
  • 29.921 inHg
  • 760 mmHg
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12
Q

Front

A
  • A front is a term used to describe the dividing line between two air masses. An approaching front will often signal its arrival with a variety of discenrable signs including:
    • Cloud formations
    • Changing wind direction and strength
    • Visibility and temperature changes
    • Air pressure changes (change in millibars)
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13
Q

Cold Front

A
  • A cold weather front has air that is colder and drier than the air in front.
  • Cold air is denser and will slide under warm air like a wedge causing the warm air to rise resulting in heavy rain or squally conditions as the swiftly rising air sheds its moisture.
  • Temperatures can drop more than 15 degrees within an hour
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14
Q

Warm Front

A
  • A warm front will tend to rise over the colder more dense air.
  • As warm air rises, the moisture it contains condenses into clouds, rain and drizzle
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15
Q

How do you use a barometer to predict weather?

A
  • Predicting weather is all about changes in air pressure
  • You want to check the reading every hour to determine if the pressure is changing or staying the same.
  • If the pressure is falling the weather is taking a turn towards storms and rain. The starting point is also important in the forecast. Higher readings indicate better weather even if the pressure is falling.
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16
Q

Sea Breeze

A
  • A sea breeze is a wind which blows locally from the sea towards the land during the daytime.
  • If the land becomes heated by the sun during the day, the air in contact with the land is heated and rises upwards.
  • Cool air flows in from the sea to replace the air rising off the land and so a circulation system is set up.
  • Sea breezes start around 1000 - 1100 hrs and end by 2000 hrs.
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17
Q

Land Breeze

A
  • At night, the land cools and the air in contact with it is cooled and flows down and out to sea.
  • Contact with the sea, which is relatively warm, heats the air which rises up and flows back towards the land where it is cooled and the circulation continues.
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18
Q

Katabatic Winds

A
  • Cold winds that flow form high elevations to the valleys and planes below.
  • Katabatic winds can cause anchor drag if anchored in a bay wiht high mountains surrounding it.
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19
Q

Anabatic Winds

A
  • Anabatic winds occur locally when air warmed by the sun rises and flows up mountain slopes and valleys.
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20
Q

Beaufort Wind Scale

How many forces on the scale?

A
  • The scale is a measurement of wind speed to observed conditions at sea or on land.
  • Marine forecasts will refer to the Beaufort Scale when issuing a forecast
  • There are 12 levels
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21
Q

Beaufort 1

A

Light Air

  • Small ripples without foam crests
  • 1 - 3 knots
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22
Q

Beaufort 3

A

Gentle Breeze

  • Large wavelets, crests start to break, scattered white
  • 7 - 10 knots
  • Wave Height 1/2 foot
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23
Q

Beaufort 4

A

Moderate Breeze

  • Small waves becoming longer, fairly frequent white horses
  • 11 - 16 knots
  • Wave height 3 1/2 feet
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24
Q

Beaufort 5

A

Fresh Breeze

  • Moderate waves, becoming longer. Many white horses some spray
  • 17 - 21 knots
  • Wave height 6 feet
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25
Q

Beaufort 8

A

Gale

  • Moderately high waves, creasts break off, visibility affected
  • 34 - 40 knots
  • Wave height 18 feet
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26
Q

Beaufort 10

A

Storm

  • Very high tumbling waves, sea looks white with large patches of foam
  • Visibility badly affected
  • 48 - 55 knots
  • Wave height 29 feet
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27
Q

What are the 3 basic cloud types?

A
  • Cirrus
  • Cumulus
  • Stratus
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28
Q

Cirrus clouds

A
  • The most common of the high cloud group of clouds (5000 - 13000m)
  • They are composed of ice and are long thin wispy clouds
  • They are usually white and predict good weather
29
Q

Cumulus cloud

A
  • Flat based, billowing clouds with vertical doming. The tops of the cumulus clouds will often have a “cauliflower-like” appearance.
  • Can be associated with good or bad weather and generally contain showers.
30
Q

Stratus Clouds

A
  • These are low clouds (up to 2,000m), grey in color and cover most of the Sky and can sometimes look like fog that does not reach the ground.
  • Mist or drizzle are associated with this formation.
31
Q

Tropical depression

A
  • A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained winds of less than 34 knots (63 km/h)
  • It has no eye and does not typically have the organization or the spiral shape of more powerful storms.
  • It is a low pressure system
32
Q

A Hurricane or Typhoon

A
  • A system with sustained winds of 34 metres per second (66 knots) or 74 miles per hour (119 km/h)
  • A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of circulation.
  • Surrounding the eye is the eyewall, an area about 16 kilometres (9.9 mi) to 80 kilometres (50 mi) wide in which the strongest thunderstorms and winds circulate around the storms center.
33
Q

Name 3 Fog types

A
  1. Advection fog, or Sea fog
  2. Radiation fog
  3. Frontal fog
34
Q

Advection Fog

A
  • Occurs when warm moist air flows over a cold sea surface.
  • This conditon is more likely to arise in the late spring, or early summer before the sea has warmed fully.
35
Q

Radiation Fog

A
  • Land based fog which occurs during cold clear nights when the land radiates the heat it absorbed during the day.
  • The cold land cools the iar in contact with it casuing dew to develop.
36
Q

Frontal Fog

A
  • May occur where two air masses of different temperatures meet. If both air masses have a high moisture content fog will form at the front between them.
37
Q

Weather forecasts are given on what VHF radio channels?

A
  • 21 B
  • 25 B
  • 28 B
  • 83 B
  • WX 1 - 9
38
Q

After A Storm

Precautions

A
  • Be aware of floating debris such as tree branches and other vegetation
  • Murky and muddy water in creeks and rivers obstructing visibility
  • Higher currents down creeks or rivers making navigation more difficult
39
Q

What are standard “Heavy Weather Preparations” on a sailboat?

A
  • Close all hatches, put washboards and hatch covers in place
  • Close seacocks
  • Hoist radar reflector
  • Secure all loose items on deck and below
  • Make sandwiches or easy to prepare food
  • Don heavy weather apparel, safety harness and lifejackets
  • Appoint lookouts as visibility can be significantly reduced
  • Plot position accurately, manoeuver away from a lee shore
  • Reduce sail and prepare trysail or heavy weather sails
  • Head for a safe haven (anchorage or marina)
40
Q

Leeshore

A
  • In rough weather there is always the danger of a leeshore on to which the wind is blowing, and the seas breaking.
  • A boat will be safer offshore in deeper water.
  • Often, what appears to be a safe harbour requires an approach to leeshore. This can result in large rolling waves at the entrance to the harbour which can cause the boat to “surf” down the waves out of control
41
Q

Line Squalls

A
  • A line squall during daylight hours is visible as a darkening line across the sky which somtimes contains short bursts of intensive rain and sudden dramatic increase in wind speed.
  • You should prepare for heavy weather which includes
    • Closing all hatches and washboards
    • Reducing sail and switch to trysail
    • Find safe haven (anchorage or marina)
42
Q

Sea Anchors

A
  • A canvas or web type bag which looks like a small parachute and is deployed off the bow of the boat using the anchor rode to keep the bow into the swell.
  • A sea anchor should be deployed with enough rode to reach the crest of the oncoming wave.
43
Q

Drogues

A
  • During strong following seas, the wave action on the stern of a vessel can cause the vessel to constantly “yaw” which will push the boat from side to side.
  • To prevent this a drogue is dragged behind a vessel (attached to the stern) which will act like a brake and assist in maintaining the boats course.
44
Q

Actions to take in Fog conditions

A
  • Immediate obtain accurate position
  • Check chart and steer a course to keep clear of hazards
  • Monitor VHF radio
  • Hoist radar reflector
  • Appoint a lookout
  • Sound the fog signal ( one long blast every two minutes)
45
Q

Weather Map

High and Low pressure map identifyers

A
  • A high-pressure system onshore is indicated by a blue “H”
  • A low-pressure system offshore is indicated by a red “L”
46
Q

Regular Marine Forecasts

A

Are issused two to four times daily, depending on the region and program and provide detailed weather informaion for the next 48 hours. It includes the following:

  • Wind speed and direction
  • Weather conditions and precipitation
  • Visibility
  • Freezing spray
  • Air temperature
47
Q

Extended Marine Forecasts

A

Provide a more general outlook of marine wind conditions, including speed and direction for the three days after the period covered by the regular marine forecast. They are issued twice daily.

48
Q

MAFOR

A

Marine FORecasts

Is a North American code used to compress meteorological and marine information for convenience during radio broadcasting. Environment Canada issues MAFOR coded forecasts for the Great Lakes and St. Lawrence and Saguenay Rivers that contain information on wind speed and direction, weather, visibility and sea state.

49
Q

NAVTEX

A

Navigational Telex

Is an international, automated direct printing service for the delivery of navigational and meteorological warnings and forecasts.

50
Q

Marine warnings and watches

A

Issued when forecast conditions warrant and are broadcast immediately and include the following:

  • Strong winds (20 - 33 kt)
  • Gale force winds (34-47 kt)
  • Storm-force winds (48-63 kt)
  • Hurricane-force (64 kt or higher)
  • Freezing spray (moderate or higher)
  • Any other relevant localized warnings (i.e. tornadoes)
51
Q

Common Marine Publications

A

Canadian Coast Guard

  • Notice to Mariners that include important information and amendments on marine charts

Canadian Hydrographic Service

  • Nautical charts
  • Tide and current tables
  • Sailing directions
  • Canadian aids to navigation system
  • Radio aids to marine navigation
  • List of Lights, and Buoys and Fog Signals
52
Q

Gust Factor

A

The ratio of the gust to the sustained wind is known as the “gust factor”

  • The gust factor during the summer is usually 1.25 or 25% of sustained winds
53
Q

Wind

A

Wind is the term for moving air. It is created when air in a higher pressure area flows into an area of lower pressure to take the place of the air that is rising away.

The more difference there is in pressure between two areas, ther more forcefully the air will flow between them - and the stronger the wind will blow.

54
Q

Geostrophic Wind

A

When the effects of the pressure gradient force and the Coriolis force combine, the result is called the “geostophic” wind.

  • In the northern hemisphere the wind around a high turns clockwise and the wind around a low turns counter-clockwise.
55
Q

Unstable Atmosphere

A

When a parcel of air cools more slowly than the surrounding atmophere, it will continue to rise because it is lighter than the air around it. The atmosphere is “unstable” because it is experiencing vertical movement.

Wind effect

  • When the atmosphere is unstable, warmer air at the surface rises and draws down some of the cold, wind air from higher in the atmosphere. This causes gusty winds, showers or thunderstorms.
56
Q

Solar Heating

Land Versus Water

A

Land warms more quickly than water, but water holds its heat longer. The differential in heating can create a small-scale system of highs and lows that alters the direction of the prevailing wind.

57
Q

How is a sea breeze formed?

A

They typically start in the morning as the heat from the sun causes the land to warm up at a faster rate than the water. This creates a “low” over the land and a “high” over the water, which causes the cool air from the sea to flow inland to repalce the warm air that is rising and flowing out to sea.

  • Sea breezes form when the prevailing winds are light around 15 knots and cloud cover is less than 50 percent
  • As the day progresses wind speed increases and wind direction shifts clockwise 50 to 60 degrees
58
Q

What are the hazards associated with sea breeze?

A
  • Sea breezes can create winds of 10 - 15 knots
  • Sea breeze can blow a fog bank toward the shore decreasing visibility
59
Q

How is a land breeze formed?

A

Land breezes form at night or during the day in colder seasons when the temperature of the air at the surface of the land drops lower than the temperature of the air at the surface of the water.

  • These temperature differences occur because land not only warms up faster than water but also cools down faster. Water on the other hand holds its heat longer.
  • The cooler air over the land creates a high pressure area, while the warmer air over the water creates an area of low pressure.
60
Q

What are the hazards associated with land breezes?

A
  • Can cause wind gusts
  • If there is enough moisture in the air, land breezes can also cause showers or thunderstorms over the water
61
Q

How is a katabatic wind formed?

A

On a clear evening heat from the surface of the earth radiates out into space, causing air temperatures near the surface to cool down. In areas sheltered by steep terrain, the air near the base of the slope stays warm longer than the air above it. This causes the cooler, heavier air near the toop of the slope to flow downward creating a strong wind.

62
Q

Waves

A

The height of waves is contingent on several factors, including the wind’s strength, its duration, and the fetch which denotes the distance it has taversed over open water.

63
Q

Where can you get weather information

A

National Weather Service Website
WX channels tuned to NOAA Weather Radio’s continuous marine weather broadcasts.

64
Q

Small Craft Advisory

A

The National Weather Service issues Small Craft Advisories when adverse wind or sea conditions are expected. Broadcasting them on NOAA Weather Radio and posting them on their website.

65
Q

Gale Warning

A

Winds between 34 and 47 knots are classifed as gale force and ppose severe dangers. When a gale is forecasted, the NWS issues a Gale Warning that every mariner should heed for their safety.

66
Q

Warm Fronts

A

Warm air is capable of holding more moisture and is less dense than cold air. When warm air advances and overtakes cooler air, it rises above it. As it ascends, it cools at higher altitudes and releases its moisture in the form of rain.

Therefore, if you observe rain and notice a shift in wind direction from southwest to northwest, its often indicateive of a warm front’s passage.

67
Q

Cold Fronts

A

Cold air tends to move faster and wedges itself under the warmer air mass, forcing the warmer air to rise rapidly. This rapid ascent leads to the release of moisture and can result in turbulent weather conditions.

This can cause thunderstorms, lightning, cold rain and possibly hail.

68
Q

ISOBARS and WIND PATTERNS

A

Isobars on weather maps help meteorologists visualize and analyze pressure patterns.
Tracing an isobar with your finger on a weather map can give you an idea of wind direction.
Air tends to flow parallel to isobars from areas of high pressure to low pressure.
The proximity of isobars to each other indicates the steepness of the pressure gradient which in turn affects wind strenght.
Closer isobars represent stronger winds.

International Bareboat Skipper (7 decks)

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