Download Three Types of Precipitation

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Three Types of Precipitation
Relief or Orographic Precipitation
• There are three reasons why air is forced upward also forming three types of
precipitation.
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• Relief Precipitation- caused by winds carrying air up over a mountain barrier.
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Convectional Precipitation
• Convectional precipitation results from the heating of the earth's surface. The warm
ground heats the air over it. As the air warms, the air molecules begin to move
further apart.
• With increased distance between molecules, the molecules are less densely packed.
Thus, the air becomes “lighter” and rises rapidly into the atmosphere.
• As the air rises, it cools. Water vapor in the air condenses into clouds and
precipitation. This type of precipitation is common in the Prairies and Ontario
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Frontal Precipitation
• When masses of air with different density (moisture and temperature characteristics)
meet, warmer air overrides colder air. The warmer air is forced to rise and if
conditions are right becomes saturated, causing precipitation. In turn, precipitation
can enhance the temperature and moisture contrast along a frontal boundary.
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• Fronts cause sudden changes in general temperature, and in the humidity and
pressure in the air. Warm fronts occur where the warm air scours out a previously
lodged cold air mass. The warm air 'overrides' the cooler air and moves upward.
Warm fronts are followed by extended periods of light rain and drizzle, because, after
the warm air rises above the cooler air (which sinks to the ground), it gradually cools
due to the air's expansion while being lifted, which forms clouds and leads to
precipitation.
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Hail
 Hail is formed when updrafts carry raindrops upwards into extremely cold areas of
the atmosphere
Hail
 There the raindrops merge and freeze. When the frozen clumps get to heavy they
fall to earth
Hail
 Hail can vary in size, from the size of a small stone to that of a baseball! So be
careful
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• Symbols on a Weather Map
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Weather Disturbances
Tropical Storms and Hurricanes
Introduction
Hurricanes are responsible for astonishing amounts of property damage and loss of
life in many regions of the world
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Hurricanes around the globe
• Atlantic - hurricanes
• Western Pacific – typhoons – highest frequency region
• Indian Ocean and Australia – cyclones
• South Atlantic - almost none
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The tropical setting where tropical storms usually form
• Subsidence (trade wind) inversion on the east side of the subtropical highs traps
cooler, moist air (marine layer) at the ocean surface
• On the western sides of the ocean basins, the marine layer tends to be warmer
and thicker due to higher ocean temperatures -- more hurricanes tend to
develop here
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Hurricane characteristics
• Sustained winds greater than 120 km/hr (74 mph)
• Average diameter = 600 km (350 mi)
• Central pressure = ~ 950 mb to 870 mb
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Hurricane Formation
Steps in the formation of hurricanes
• Tropical disturbance associated with an easterly wave in the upper air winds
• Tropical depression -- at least one closed isobar
• Tropical storm -- winds greater than 37 mph
• Hurricane (typhoon, cyclone) -- winds greater than 74 mph
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Conditions Necessary for Hurricane Formation
• Warm ocean water (> 27oC (81oF))
• Latent heat release
• Most frequent in late summer and early autumn
• Formation equator ward of 5o
• Unstable atmosphere without vertical shear
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• Unstable atmosphere without vertical shear
• Once formed – self-propagating system until it runs out of warm water
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Hurricane Destruction and Fatalities are caused by several factors:
Wind
Heavy rain
Tornadoes
• Right front quadrant
Storm surge
• Rise in water level associated with pressure drop
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Thunder and Lighting Storms
Lighting
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Tornados
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