CANADIAN COAST GUARD AUXILIARY - PACIFIC NAVIGATION TRAINING Section 11 Weather

CANADIAN COAST GUARD AUXILIARY - PACIFIC Table of Contents Section 1Types of Navigation Section 2Terrestial Coordinates Section 3Charts Section 4 Compass Section 5Nautical Publications Section 6Navigational Aids

CANADIAN COAST GUARD AUXILIARY - PACIFIC Table of Contents Section 7 Buoyage Section 8Position Lines and Fixes Section 9Tides Section 10Currents Section 11Weather

CANADIAN COAST GUARD AUXILIARY - PACIFIC Weather

CANADIAN COAST GUARD AUXILIARY - PACIFIC Atmospheric Pressure

CANADIAN COAST GUARD AUXILIARY - PACIFIC Atmospheric Pressure The standard atmosphere (symbol: atm) is a unit of pressure and is defined as being precisely equal to kilopascals, millibars, or inches of mercury. The pressure gradient between a high pressure area and a low pressure area governs the strength of the wind, the wind blowing from high pressure to low pressure. The greater the gradient the stronger the wind.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Atmospheric Pressure An extreme example is the centre of a hurricane which can go as low as 94.8 kilopascals. The pressure gradient is huge, causing the winds to blow at 100 to 150 knots (nautical miles per hour).

CANADIAN COAST GUARD AUXILIARY - PACIFIC Mean Sea Level Pressure Where air masses meet, there are well- marked boundary zones called fronts. This is where most cloud and precipitation occurs. In the northern hemisphere the circulation is anticlockwise around low pressure and clockwise around high pressure. The air flows almost parallel to the isobars but actually degrees inwards towards the low pressure.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Mean Sea Level Pressure 15 year average Mean Sea Level Pressure for June July August 15 year average Mean Sea Level Pressure for December January February

CANADIAN COAST GUARD AUXILIARY - PACIFIC Global Circulation The Earth rotates at a constant rate, and the winds blow, the transfer of momentum between Earth/atmosphere /Earth must be in balance; and the angular velocity of the system maintained. The atmosphere is rotating in the same direction as the Earth but westerly winds move faster and easterly winds move slower than the Earth's surface.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Global Circulation Remember winds are identified by the direction they are coming from, not heading to!

CANADIAN COAST GUARD AUXILIARY - PACIFIC Weather Fronts Where air masses meet, there are well- marked boundary zones called fronts. This is where most cloud and precipitation occurs. In the northern hemisphere the circulation is anticlockwise around low pressure and clockwise around high pressure. The air flows almost parallel to the isobars but actually degrees inwards towards the low pressure.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Weather Fronts There are three types of front: 1. Warm front 2. Cold front 3. Occlusions and Occluded Fronts

CANADIAN COAST GUARD AUXILIARY - PACIFIC Warm Fronts When a warm moist air mass rises above a cold air mass, a warm front forms. The gradient of the front is very shallow. Warm fronts occur at the forward edge of a depression (a low- pressure system).

CANADIAN COAST GUARD AUXILIARY - PACIFIC Warm Fronts

CANADIAN COAST GUARD AUXILIARY - PACIFIC Warm Fronts

CANADIAN COAST GUARD AUXILIARY - PACIFIC Cold Fronts

CANADIAN COAST GUARD AUXILIARY - PACIFIC Cold Fronts

CANADIAN COAST GUARD AUXILIARY - PACIFIC Cold Fronts A cold front marks the advance of colder air undercutting warm air. The gradient of the cold front is steeper than that of a warm front, and the rainfall is usually heavier. Thunderstorms sometimes form along a cold front.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Occluded Fronts Depressions and other frontal systems have a three-dimensional structure. Most depressions weaken when the cold front catches up with the warm front and cuts it off from the ground. If the cold front rises over the warm front, this is a warm occlusion. If the cold front undercuts the warm front this is a cold occlusion.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Occluded Fronts Weather systems grow mature and decay and as they do, new ones are created. This creates families of weather systems.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Wind is primarily the result of uneven heating of the earth’s surface, which causes large hotter areas and large cooler areas.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Calm Sea like a mirror

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Light air Ripples with the appearance of scales are formed, but without foam crests.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Light Breeze Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Gentle Breeze Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Moderate Breeze Small waves, becoming larger; fairly frequent white horses.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Fresh Breeze Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Strong Breeze Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Near Gale Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Gale Moderately high waves of greater length; edges of crests begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Severe Gale High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Storm Very high waves with long over- hanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Violent Storm Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force FORCE EQUIVALENT SPEED DESCRIPTION SPECIFICATIONS FOR USE AT SEA 10 m above ground miles/hour knots Hurricane The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Sea Breeze A sea-breeze (or onshore breeze) is a wind from the sea that develops over land near coasts. It is formed by increasing temperature differences between the land (which heats up faster) and water (which warms slower) which create a pressure minimum over the land due to its relative warmth and forces higher pressure, cooler air from the sea to move inland.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Sea Breeze It generally occurs in the afternoon.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Land Breeze A land-breeze (or offshore breeze) is a wind to the sea that develops over land near coasts. It is formed by increasing temperature differences between the land (which cools faster) and water (which cools slower) which create a pressure minimum over the sea due to its relative warmth and forces higher pressure, cooler air from the land to move offshore.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Land Breeze It generally occurs in the very early morning.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Katabatic Winds A katabatic wind, from the Greek word katabatikos meaning "going downhill", is a wind that blows down a topographic incline such as a hill, mountain, or glacier. The cold form of katabatic wind originates in a cooling, either radiatively or through vertical motion, of air at the top of the mountain, glacier, or hill.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Katabatic Winds Since the density of air increases with lower temperature, the air will flow downwards, warming adiabatically as it descends, but still remaining relatively cold.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Wind Force & Sea State The visible effects of the wind on the sea will be modified by the relative directions of wind and tide. If the wind and tide are in opposite directions, then a larger chop will be created, giving the impression of the wind being stronger. If wind and tide are in the same direction, the amount of sea will be reduced, giving the impression of the wind being less.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Sea and Swell Sea is the effect of wind passing over the water locally. Swell is only found in the open ocean and will be effects of weather systems, hundreds of miles away.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog Fog is a cloud in contact with the ground. Fog differs from other clouds only in that fog touches the surface of the Earth. The same cloud that is not fog on lower ground may be fog where it contacts higher ground such as hilltops or mountain ridges. Fog is distinct from mist only in its density.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog Fog is defined as cloud which reduces visibility to less than 1 nautical mile, where as mist is that which reduces visibility to more than 1 nautical mile.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog Fog forms when water vapor in the air at the surface begins to condense into liquid water. Fog normally occurs at a relative humidity of 100%. This can be achieved by either adding moisture to the air or dropping the ambient air temperature. Fog can form at lower humidities, and fog can sometimes not form with relative humidity at 100%.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area significantly cooler. It's most common at sea when tropical air encounters cooler waters, or in areas of upwelling.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Upslope Fog

CANADIAN COAST GUARD AUXILIARY - PACIFIC Other Types of Fog

CANADIAN COAST GUARD AUXILIARY - PACIFIC Fog “Slight Sea, Low Swell, Cloudy, Fine and Clear”

CANADIAN COAST GUARD AUXILIARY - PACIFIC Precipitation

CANADIAN COAST GUARD AUXILIARY - PACIFIC Orographic Rain Orographic rain (or relief rain) is caused when the warm moisture-laden wind blowing in to the land from the sea encounters a natural barrier such as mountains. This forces the wind to rise. With gain in altitude, the air expands dynamically due to a decrease in air pressure. Due to this the wind experiences a decrease in temperature, which results in the increase of the relative humidity.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Orographic Rain This causes condensation of the water vapour into water droplets to form clouds. The relative humidity continues to increase until the dewpoint reaches the level of condensation, causing air to be saturated. This height where the condensation occurs is called the level of condensation. When the cloud droplets become too heavy to be suspended, rain falls.

CANADIAN COAST GUARD AUXILIARY - PACIFIC Orographic Rain in Howe Sound