what is weather? weather patterns weather forecasts

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What is Weather? Weather Patterns

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Page 1: What is Weather? Weather Patterns Weather Forecasts

What is Weather?Weather PatternsWeather Forecasts

Page 2: What is Weather? Weather Patterns Weather Forecasts

Weather : state of the atmosphere at a specific time and place

Weather describes conditions such as air pressure, wind, temperature and amount of moisture in air

Sun provides almost all of earth’s energy It encourages evaporation, which condenses

and water returns to earth’s surface The land absorbs the heat and warms the

atmosphere and causes uneven heating of atmosphere

Air and water currents are caused by sun’s uneven heating

Page 3: What is Weather? Weather Patterns Weather Forecasts

Temperature is a measurement of the motion of molecules

The more movement, the greater the temperature

Less movement of molecules, the cooler the temperature

Page 4: What is Weather? Weather Patterns Weather Forecasts

Air moving in a specific direction is called wind

Air near the surface is warmed by conduction◦ Air expands, becomes less dense, rises◦ (warm rising air forms low pressure at surface)

Cool dense air tends to sink that yields to high pressure areas

Wind results because air moves from areas of high to low pressure

Page 5: What is Weather? Weather Patterns Weather Forecasts

Wind direction is measured by a wind vane

(points in the direction from which wind is blowing)

Wind is measured by an anemometers which has cups that spin with wind strength

Page 6: What is Weather? Weather Patterns Weather Forecasts

When water evaporates into the atmosphere it fits into spaces

The amount of water vapor present in an air mass is called humidity

Warmer air can hold more water vapor

Cooler air holds less water If temperature is cool enough water vapor condenses and the air mass is considered saturated

Page 7: What is Weather? Weather Patterns Weather Forecasts

Relative humidity is a measure of the amount of water vapor present in the air compared to amount needed for saturation at a specific temperature

Relative humidity is dependent on the specific temperature and changes as temperature changes (warmer air holds more water than cooler air)

If a cubic meter of air at 25˚C is saturated with 22 g of H2O it is said to have a RH of 100%

If it has 11 g of H20 it has RH of 50%

Page 8: What is Weather? Weather Patterns Weather Forecasts

When temperature drops, less water vapor can be held and it condenses to a liquid or forms ice (depending of the temperature)

The temperature at which condensation occurs is called Dew Point

Page 9: What is Weather? Weather Patterns Weather Forecasts

Warm air rises

As air rises it cools

Cooler air doesn’t hold as much water and if it cools to saturation point, its dew point is met

Water droplets form around nuclei of dust, smoke, smog to form clouds after saturation point is met

Page 10: What is Weather? Weather Patterns Weather Forecasts

Classified by shape and height

Shape and height of clouds vary with temperature, pressure, and amount of water vapor present

Page 11: What is Weather? Weather Patterns Weather Forecasts

3 Main types Stratus (form layers or smooth even sheets)

◦Found at lower altitudes and may be associated with fair weather or rain or snow

◦Fog is low stratus clouds formed by saturation near ground level

Page 12: What is Weather? Weather Patterns Weather Forecasts

Stratus Clouds : low and flat

Page 13: What is Weather? Weather Patterns Weather Forecasts

Cumulus clouds: masses of puffy white clouds often with flat bases

Sometimes they tower to great heights and can be associated with fair weather or thunderstorms

Page 14: What is Weather? Weather Patterns Weather Forecasts

http://images.search.yahoo.com/search/images;_ylt=A2KJkIbcDaRP5HIAdx2jzbkF?fr2=xpl&p=cumulus+clouds&fr=slv1-mdp&vm=r

Page 15: What is Weather? Weather Patterns Weather Forecasts

Cirrus clouds: appears fibrous curly, wispy

They are high, thin, white feathery made of ice crystals

Associated with fair weather, or can indicate approaching storms

Page 16: What is Weather? Weather Patterns Weather Forecasts

http://images.search.yahoo.com/search/images;_ylt=A2KJke4JFqRPyHUAIQWjzbkF?fr2=xpl&p=cirrus+clouds&fr=slv1-mdp&vm=r

Page 17: What is Weather? Weather Patterns Weather Forecasts

Prefixes help describes the height of clouds

Cirro (high clouds) Alto (middle clouds) Strato (low level clouds) Some combine the altitude with stratus or

cumulus Cirrostratus (high clouds-fair weather or

warning of approaching storm) Altostratus: not thick, middle layers,

sunlight filters through

Page 18: What is Weather? Weather Patterns Weather Forecasts

Nimbus (dark rain cloud) refers to clouds that produce rain or snow

Because they are thick, you can’t see through them

Cumulus clouds grows into thunderstorms called cumulonimbus (12 miles up)

Nimbostratus clouds are layered clouds that can bring long steady rain or snowfall

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Page 21: What is Weather? Weather Patterns Weather Forecasts

http://images.search.yahoo.com/search/images;_ylt=A2KJkPkgD6RPrFQAcAmjzbkF?p=nimbostratus%20clouds&ei=utf-8&n=30&x=wrt&tab=organic&fr2=sg-gac&sado=1&vm=r

Page 22: What is Weather? Weather Patterns Weather Forecasts

Water falling from clouds is known as precipitation

Water grows around nuclei (dust, smoke) and grow larger until they fall to ground

Raindrop size depends on strength of updrafts in cloud (strong updrafts let condensed water move up and down, growing in size)

If the temperature is warm as droplet falls it can evaporate before reaching surface

Page 23: What is Weather? Weather Patterns Weather Forecasts

Air temperature determines whether water forms rain, snow, sleet, or hail

Above freezing falls as rain Snow forms when temperatures is so cold that water vapor changes directly to a solid

Sleet forms when raindrops pass through layers of freezing air near surface forming ice pellets

Page 24: What is Weather? Weather Patterns Weather Forecasts

Hail is precipitation in the form of lumps of ice

Forms in cumulonimbus clouds when thunderstorms develop

Hailstones grow as they are tossed up and down in cloud

Can grow from 2.5 cm (1inch) to softball size

Page 25: What is Weather? Weather Patterns Weather Forecasts

Relative humidity helps determine whether you will have a dry or wet day

The temperature of atmosphere determines the form of precipitation

Winds are dependent on rising air

Page 26: What is Weather? Weather Patterns Weather Forecasts

Air Mass: large bodies of air that have properties similar to the part of the earth’s surface over which they develop◦ Continental polar: develops over continent

(dry) and cold◦ Continental tropics: develops over continent

(dry) and warm◦ Maritime polar: develop over body of water

(moisture) and is cold◦ Maritime tropics: develop over water and

warm

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Page 28: What is Weather? Weather Patterns Weather Forecasts

Winds blow from high pressure to low pressure

Pressure is measured by amount of air above the surface

As winds blow into low pressure systems, the rotation of earth causes low pressure systems to move counter-clockwise called cyclone

Low pressure are areas of rising air (temperature decreases, clouds form, precipitation probable)

Page 29: What is Weather? Weather Patterns Weather Forecasts

Winds that blow from High pressure spiral clockwise in northern hemisphere (anticyclone)

High pressure is associated with fair weather

Barometers measure the pressure above the surface

Variations of pressure in atmosphere affects weather

Sinking air in high pressure systems indicates warming air mass, less clouds (or no) usually is fair weather

Page 30: What is Weather? Weather Patterns Weather Forecasts
Page 31: What is Weather? Weather Patterns Weather Forecasts

Boundary between two air masses of different density, moisture, or temperature is called a front

Cloudiness, precipitation and storms sometimes occur

Page 32: What is Weather? Weather Patterns Weather Forecasts

Cold front is shown on map with a blue line with triangles pointing in direction of air mass movement ( when colder air advances toward warm air)

Cold air wedges and lifts warm air upward Warm air cools, clouds form (if enough

moisture) Thunderstorms form when temperature

differences are large

Page 33: What is Weather? Weather Patterns Weather Forecasts

Warm front forms when warm air advances over heavier colder air

It is written with red lines and semi-circles pointing in the direction of the warm air advances

Page 34: What is Weather? Weather Patterns Weather Forecasts

This involves 3 air masses of different temperature

Cold air moves toward cool air with warm air between the two

Colder air is forced up, closing off the warm air from the surface

Shown on maps with purple lines with triangles and semicircles

Page 35: What is Weather? Weather Patterns Weather Forecasts

When boundary between air mass stop advancing

Remain in same place for several days, producing light wind and precipitation

Shown as alternating warm and cold front symbols

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Page 38: What is Weather? Weather Patterns Weather Forecasts

Thunderstorms : occurs when warm moist air rises along fronts

Cumulonimbus clouds form that can reach heights of 12 miles up

In cloud smaller droplets of water collide to form bigger ones

As droplets fall, the air is cooler, and brings about updrafts of warmer air causing strong winds

Hail forms in clouds if temperature is below freezing in the clouds and droplets freeze in up and down drafts

Page 39: What is Weather? Weather Patterns Weather Forecasts
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Flash flooding occurs when streams can’t contain all the water

Strong winds originating from the thunderstorm causes damage

Hail damages property Destroy crops

Page 42: What is Weather? Weather Patterns Weather Forecasts

Lightning: warm air is lifted faster in clouds when clouds form as cooler air sinks

Movement of air can cause different parts of the cloud to be oppositely charged

Currents then flow in opposite direction causing lightning

Lightning can occur cloud to cloud, cloud to ground and within a cloud

Page 43: What is Weather? Weather Patterns Weather Forecasts

Lightning can reach temperatures of 30,000 °C (sun’s photosphere is 6000°C)

This extreme heat causes air around the lightning to expand rapidly

Then it cools quickly and contracts That rapid movement of the molecules

forms sound waves heard as thunder

Page 44: What is Weather? Weather Patterns Weather Forecasts

Tornado’s are violent rotating columns of air in contact with the ground

In thunderstorms, wind at different heights blow at different speeds

These differences are called wind shear and rotates the column parallel to ground

It can create a funnel cloud as it rotates upward

If it touches the ground it is called a tornado

Page 45: What is Weather? Weather Patterns Weather Forecasts

Hurricanes are large swirling low pressure system that originates over warm oceans

It moves warm air away from the ocean to the atmosphere as wind

Typhoons and cyclones are another name In the Atlantic Ocean hurricanes develop

near Africa and winds direct them to U.S. Gain strength as move over warm oceans When hurricanes reach land they cause

destruction and damage, tornados spin off but land cuts off their energy source, so they are de-energized and loose power

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Blizzards in the northwest are common Temperatures must be low as well as

visibility (400m) caused by blowing winds (56 mph)

Page 49: What is Weather? Weather Patterns Weather Forecasts

Meteorologist: person who studies weather

Take data measurements like temperature, air pressure, winds, humidity, and precipitation

Balloons weather satellites, doppler radar and computers help meteorologists

They produce weather maps to help predict weather

Page 50: What is Weather? Weather Patterns Weather Forecasts

Station models: weather data is recorded in combination of weather symbols at station models

Temperature: lines of equal temperature on a weather map are called isotherms

Pressure: lines on map with equal pressure is called an isobar◦ If the isobars are close together, usually

high winds are present◦Large pressure differences over small area

causes strong winds◦ Isobars also tell you areas of high and low

pressure

Page 51: What is Weather? Weather Patterns Weather Forecasts

Shows high and low pressure Shows movements of types of fronts Can get a big picture of what is going

on weather-wise

Page 52: What is Weather? Weather Patterns Weather Forecasts