Weather (Ch. 13)

Front

A boundary between two air masses.

Fog

A cloud that forms near Earth's surface. Is a suspension of water droplets or ice crystals close to Earth's surface. Reduces visibility, the distance a person can see into the atmosphere.

High-Pressure System

A large body of circulating air with high pressure at its center and lower pressure outside of the system. --Associated with clear skies and fair weather.

Low-Pressure System

A large body of circulating air with low pressure at its center and higher pressure outside of the system. --Forms clouds, and sometimes precipitation.

Radiosonde

A package of weather instruments carried kilometers above the ground by a weather balloon.

Doppler Radar

A specialized type of radar that can detect precipitation as well as the movement of small particles, which can be used to approximate wind speed.

Blizzard

A violent winter storm characterized by freezing temperatures, strong winds, and blowing snow.

Visible Light Images (Satellite Images)

A visible light image shows cloud coverage.

Air Masses

Air masses are classified by the temperature and moisture characteristics.

Polar Air Masses

Air masses that form in cold regions are called polar.

Arctic Air Masses

Air masses that form near the North Pole.

Antarctic Air Masses

Air masses that form near the South Pole.

Continental Air Masses

Air masses that form over land are referred to as continental air masses.

Maritime Air Masses

Air masses that form over water are referred to as maritime air masses.

Wind

Air moves from areas of high pressure to areas of low pressure, creating wind. Wind direction is the direction from which the wind is blowing (where it came from). Measure wind speed using an anemometer.

Thunderstorms

Also known as electrical storms because of their lightning. Have warm temperatures, moisture, and rising air which may be supplied by a low-pressure system. Have a three-stage life cycle: • Cumulus Stage -------Dominated by cloud formation and updrafts and then downdrafts. • Mature Stage -------Heavy winds, rain, and lightning dominate the area. • Dissipation Stage ------Updrafts stop, winds die down, lightning ceases, and precipitation weakens.

Infrared Image (Satellite Images)

An infrared image shows infrared energy, which gives information about cloud height and atmospheric temperature.

Stratus Clouds

Appear flat, white, and layered Can be up to 2,000m in attitude

Cumulus Clouds

Appear fluffy, heaped, or piled up 2,000 to 6,000 m in altitude

Cirrus Clouds

Appear wispy Above 6,000 m in altitude

Hurricane

Are the most destructive storms on Earth. Typically from in later summer over warm, tropical ocean water. A typical hurricane is 480 km in diameter. In the center of a hurricane is the eye, an area of clear skies and light winds. In other parts of the world, hurricanes have different names; in Asia they are called a typhoon; in Australia they are called a tropical cyclone.

Surface Report

Describes a set of weather measurements made on Earth's surface. --Weather variables are measured by a weather station (a collection of instruments that report temperature, air pressure, humidity, precipitation, and wind speed and direction).

Upper-Air Report

Describes when, temperature, and humidity conditions above Earth's surface. --Measured by a radiosonde, a package of weather instruments carried kilometers above the ground by a weather balloon.

Computer Models

Detailed computer programs that solve a set of complex mathematical formulas. --These formulas predict what temperatures and wind might occur, when and where it will rain and snow, and what types of clouds will from.

Arctic Air Masses (cA)

Form over Siberia and that Arctic Cold, dry air

Continental Polar Air Masses (cP)

Form over central Canada. Bring cold temperatures in winter and cool weather in summer. Cold, dry air

Maritime Polar Air Masses (mP)

Form over the north Atlantic and north Pacific Oceans. Cold and humid air. Often bring cloudy, rainy weather.

Maritime Tropical Air Masses (mT)

Form over the western Atlantic Ocean, the Gulf of Mexico, and the eastern Pacific Ocean. Moist, hot air. During the summer, they bring hot, humid air to the southeastern U.S. and can bring heavy snowfall in winter.

Occluded Fronts (Blocked Front)

Forms when a fast-moving cold front catches up with a slow-moving warm front. Usually bring precipitation.

Warm Fronts

Forms when less dense warmer air moves toward cold, denser air. The warm air rises and water vapor condenses, creating a wide blanket of clouds, often bringing steady rain or snow for several hours or even days. Brings warmer temperatures, but also causes the wind to shift directions.

Stationary Front

Forms when the boundary between to air masses stalls. Cloudy skies and light rain occur.

Continental Tropical Air Masses (cT)

From in the tropics over dry, desert land. Hot and dry air. Bring clear skies and high temperatures.

Isobars

Lines that connect all places on a map where pressure has the same value. --Show the location of high- and low-pressure systems. --Can also tell about wind speeds because when lines are close together, winds are strong.

Isotherms

Lines that connect places with the same temperature on a map. --Show which areas are warm and which are cold.

Sleet

May originate as snow which melts as it falls through a layer of warm air and refreezes when it passes through a layer of below-freezing air.

Torndado

Most tornadoes have a diameter of several hundred meters, but the largest can exceed 1,500 m in diameter. Winds can reach speeds of more than 400 km/h. Form when thunderstorm updrafts begin to rotate. Tornadoes are classified based on the damage that they cause. ---We use the Fujita scale.

Rain

Precipitation that reaches Earth's surface as droplets of liquid water.

Snow

Precipitation that reaches Earth's surface as sold, frozen crystals of water.

Hail

Reaches Earth's surface as large pellets of ice. Starts as a small piece of ice that is repeatedly lifted and dropped by an updraft within a cloud. A layer of ice is added with each lifting. When it becomes too heavy for the updraft to lift, it falls to Earth.

Severe Weather Warning

Severe weather is already occurring.

Severe Weather Watch

Severe weather is possible.

Station Model

Station model diagrams display data from many different weather measurements for a particular location.

Humidity

The amount of water vapor in the air. --Often measured in grams per cubic centimeter (g/cm3). --When humidity is high, there is more water vapor in the air. On a high humidity day, your skin

Relative Humdity

The amount of water vapor present in the air compared to the maximum amount of water vapor the air could contain at that temperature. --Warm air can contain more water vapor than cold air. --Measured using a psychrometer and is given as a percent. --Air with a relative humidity of 100% cannot contain any more moisture and dew and rain will from. --Air that contains only half of the water vapor that it could hold is said to have a relative humidity of 50%.

Weather

The atmospheric conditions, along with short-term changes, or a certain place at a certain time.

Tornado Alley

The central United States, from Nebraska to Texas, experiences the most tornadoes and has been nicknamed Tornado Alley.

Air Pressure

The force that a column of air applies on the air or a surface below it. Air pressure decreases as altitude increases. Measured with an instrument called a barometer. Typically measured in millibars.

Air Temperature

The measure of the average kinetic energy of molecules in the air. When temperature is high, molecules have a high kinetic energy.

The Water Cycle

The series of natural processes by which water continually moves among oceans, land, and the atmosphere.

Dew Point

The temperature at which air is saturated and condensation can occur. --When the temperature of air decreases, it can hold less moisture.

Tropical Air Masses

Warm air masses that form in the equatorial regions are called tropical.

Clouds

Water droplets or ice crystals suspended in the atmosphere.

Precipitation

Water, in liquid or solid from, that falls from the atmosphere.

Severe Weather

Weather events that can major damage, injuries, and death.

Weather Variables

Weather variables are used to help describe the weather. --Temperature, rainfall, air pressure, wind speed and direction, humidity, cloud coverage, and precipitation.

Cold Fronts

When a colder air mass moves toward a warmer air mass, a cold front forms. The cold air pushes underneath the warm air mass and the warm air rises and cools. Water vapor condenses and cloud form Showers and thunderstorms often from along cold fronts.

Condensation

When water changes from a gas to a liquid.

Evaporation

When water changes from a liquid to a gas.

Infiltration

When water on the ground enters the soil.