Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced...
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![Page 1: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/1.jpg)
Weather Maps & Fronts
• Refers to the state of the atmosphere at a specific time and place.
• Influenced by pressure systems (high and low) and fronts.
• Describes conditions such as air pressure, wind, temperature,
and the amount of moisture in the air.
• Is caused by heat energy from the sun.
![Page 2: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/2.jpg)
Air mass
• Large body of air that has the properties similar to the part of Earth’s surface over which it develops.
• Changes in weather result from movement of air masses.
Weather Patterns
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![Page 4: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/4.jpg)
Low Pressure System
When air is heated, it becomes less dense– Therefore, it rises, leaving behind an area
where there is less air.– Called a low pressure area– Rising air carries moisture with it. As a result,
low pressure is usually associated with clouds and rain.
– Indicated by a L on a weather map.– Troughs of low pressure are important because
they sometimes lead to the development of a low pressure system. Troughs are indicated by lines (sometimes purple, black or green) with no triangles or semicircles.
![Page 5: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/5.jpg)
High Pressure System
As air cools, it becomes more dense– It falls, creating an area where there
is more air– Called a high pressure area– Very little moisture in this air, so
usually associated with clear, sunny days.
– Indicated by a H on a weather map.
![Page 6: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/6.jpg)
Isobars
Lines that connect points of equal atmospheric pressure.
Isobars close together mean high wind.
Isobars far apart mean light wind.
Isotherms (iso – same, therm – heat)
Lines that connect locations of equal
temperature.
![Page 7: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/7.jpg)
Front
• A boundary between two air masses of different
density, moisture or temperature
• Cloudiness, precipitation and storms may occur at
frontal boundaries
• Four types of fronts:
cold, warm, occluded and
stationary
![Page 8: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/8.jpg)
Cold fronts
• Cold front – shown on a map as a blue line with
triangles
• Occurs when colder air advances toward warm air.
• Cold air wedges under the warm air
• This lifts the warm air, cools it and clouds form.
• If the temperature difference is large, thunderstorms
and tornadoes may form
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Warm fronts
• Warm fronts form when lighter, warmer air
advances over heavier, colder air.
• Shown as a red line with red semicircles.
![Page 11: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/11.jpg)
Occluded fronts
• Involves three air masses of different
temperatures – cold, cool and warm
• Shown on maps as purple lines with triangles
and semicircles.
• Colder air forces the warm air upward, closing
off the warm air from the surface.
![Page 12: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/12.jpg)
Occluded Front
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Stationary Front• Occurs when a boundary between air masses stops
advancing.
• May remain in the same place for several days,
producing light wind and precipitation.
• Shown on map as alternating red and blue line. Red
semicircles point toward the cold air and blue
triangles point toward the warm air.
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Stationary Front
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Severe Weather
• Sinking rain - cooled air and strong updrafts of
warmer air cause the strong winds associated with
thunderstorms.
• Hail also may form as ice crystals alternately fall to
warmer layers and are lifted into colder layers
• May cause flooding, flash floods, strong winds
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• Thunderstorms – occur in warm moist air masses and
along fronts.
• Winds stronger than 89km/hour – severe thunderstorm.
![Page 17: Weather Maps & Fronts Refers to the state of the atmosphere at a specific time and place. Influenced by pressure systems (high and low) and fronts. Describes.](https://reader035.fdocuments.net/reader035/viewer/2022062303/5516986e550346f6208b4983/html5/thumbnails/17.jpg)
Severe Weather
• Lightning - Inside a cloud, liquid and ice particles
collide causing the buildup of an electrical charge.
When the charge becomes large enough, it creates a
“spark” that allows the electrons to move. The
current flows between regions of opposite electrical
charge. Lightning can occur within a cloud, between
clouds or between the cloud and the ground.
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Thunder
• Results from the rapid heating of air around a bolt of
lightning.
• The extreme heat of lightning causes the air around
the lightning to expand rapidly. Then it cools quickly
and contracts.
• The rapid movement of the molecules form sound
waves
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Tornado
• A violent, whirling wind that moves in a narrow path
over land.
• Wind moving in different directions (shearing)
creates a rotating column
• Ranked on the Fujita scale according to how much
damage occurs F0, F1, F2, F3, F4, F5
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Severe Weather
• Hurricane – the most powerful storm
• Large swirling low pressure system that forms over the warm
Atlantic ocean
• Must have winds of at least 119 km/hour
• Called typhoons in the Pacific and cyclones in the Indian Ocean.
• Lose power when they reach land.
• The Saffir-Simpson Hurricane Wind Scale is a category 1 to 5
rating based on wind speed.
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Severe Weather
• Blizzards – winter storm with winds over 56 km/h, low
temperature, visibility less than 400m, with falling or
blowing snow.
• These conditions must persist for more than 3 hours.
10 min
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Severe Weather Safety
• Weather Advisories - are sort of in between a WATCH and WARNING.
The expected weather condition has a pretty good chance of occurring,
even a likely chance of occurring, but typically an advisory is used for
“less” severe type of weather conditions.
• Severe weather watch – when conditions are favorable for severe
weather.
• Severe weather warning – severe weather already exists.