Chapter 13

Front

A boundary between two air masses. As wind carries an air mass away from the area where it formed the air mass will eventually collide with another air mass. Drastic weather changes often occur at fronts as air masses collide. Changes in temperature, humidity, cloud types, wind, and precipitation are common at fronts. The kinds of air masses are cold fronts, warm fronts, stationary fronts, and occluded fronts. Cold and warm fronts form at the edges of air masses.

High-Pressure System

A large body of circulating air with high pressure at its center and lower pressure outside of the system. Air moves from high pressure to low pressure, the air inside the system moves away from the center. Dense air sinks, bringing clear skies and fair weather.

Low-Pressure System

A large body of circulating air with low pressure at its center and a higher pressure outside of the system. This causes the air inside the low-pressure system to rise. The rising air cools and the water vapor condenses, forming clouds and sometimes precipitation like rain or snow.

Meteorologist

A scientist who studies weather by using specialized instruments measure conditions of the atmosphere. These instruments are like thermometers to measure temperature, barometers to measure air pressure, psychrometers to measure relative humidity, and anemometers to measure wind speed. Meteorologists could understand and interpret the weather conditions with data gathered by the specialized instruments.

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. Doppler radar can estimate wind speed by the movement of precipitation being caused by wind. This is especially important during severe weather, such as tornadoes and hurricanes.

Blizzard

A violent winter storm characterized by freezing temperatures, strong winds, and blowing snow. Winter weather could be severe and hazardous. During a blizzard, swirling snow reduces visibility, and freezing temperatures can cause frostbuite or hyporthermia.

Tornado

A violent, whirling column of air in contact with the ground. Most tornadoes have a diameter of several hundred meters. The intense, swirling winds with tornadoes can reach speeds of more than 400 km/h. These winds are strong enough to send cars, trees, and even entire houses flying. Tornadoes could last from hours to several days. Tornado forms when thunderstorms updraft begins to rotate. Tornado alley is located from Nebraska to Texas in the US. Tornadoes are classified by the Fujito Scale of F0 to F5. From causing light damges to demolishing concrete and steel buildings.

Hurricane

An intense tropical storm with winds exceeding 119 km/h. These are the most destructive storms on Earth. Like tornadoes, hurricanes have a circular shape with intense, swirling winds. Hurricanes typically form in late summer over warm, tropical ocean water. A typical hurricane is 480 km across, more than 150,000 times larger than a tornado. Damages from hurricanes are like strong winds and flooding. Hurricanes are called typhoons in Asia and tropical cyclones in Australia.

Stratus

Clouds that are flat, white and layered and altitudes up to 2,000m up. Low clouds with a uniform gray. Covers the sky completely. When it is on the ground, it is called fog. This cloud is related to wet conditions. Clouds are created by water vapor condensing on small particles like dust, smoke, or salt.

Cumulus

Clouds that are fluffy, heaped or piled up and from 2,000 to 6,000m in altitude. Puffy white or light gray colored. The usual thing that pops up as a cloud. Seen during fair weather. When it gets darker and the top becomes a cauliflower like, rain is coming. Clouds are created by water vapor condensing on small particles like dust, smoke, or salt.

Cirrus

Clouds that are wispy, long, and thin. Above 6,000m up in altitude. Made of ice crystals and is high in the skies. Often seen during fair weather. if there are a lot of cirrus clouds, that means a warm front is coming. Clouds are created by water vapor condensing on small particles like dust, smoke, or salt.

Cumulonimbus Cloud

Clouds that grows very tall in the sky. Can grow up to 10km high. These are thunderstorm clouds. This cloud's weather associates with heavy rain, snow, hail, lighting, and sometimes even tornadoes. Airplanes fly through these clouds. Clouds are created by water vapor condensing on small particles like dust, smoke, or salt.

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. Cloud amounts and visibility are measured by humans observing them. This is used when making a station model and weather map.

Upper-Air Report

Describes wind, temperature, and humidity conditions above Earth's surface. These atmospheric conditions are measured by a radiosonde, a package of weather instruments carried many kilometers above the ground by a weather balloon. Radiosonde reports are made twice a day at hundreds of locations around the world at the same time. This is used when making a station model and weather map.

Computer Model

Detailed computer programs that solve a set of complex mathematical formulas. The formulas predict what temperatures and winds might occur, when and where it will rain and snow, and what types of clouds will form. These machines help the making of weather forecasts. Government meteorologist offices exchange weather measurements throughout the day. Weather maps and forecasts are made using computer models.

Cold Front

Form when colder air masses move toward warmer air masses. Creates clouds by condensation. This front has weather like showers and thunderstorms, give rise to severe storms. When this front passes by, the temperature could decrease as much as 10 degrees Celcius. The temperature is usually low with this front. The winds are gusty and change direction.

Warm Front

Form when less dense, warmer air moves toward colder, denser air. The warm air rises as it glides above the cold air mass. Water vapor condenses to create a wide blanket of clouds. This front has weather of steady rain or snow for several hours or even days. This front usually brings warm and humid temperatures. This front causes the wind to shift directions.

Lake Effect Snow

Forms when cold air passes over the warmer waters of a lake. Water holds on to heat more than air. As a result, cold air passes over much warmer water. This causes some lake water to evaporate into the air and warm it, while the cooler, moist air forms clouds. The air moves away from the lake and over the land. When it moves over the land, it releases all that moisture on the ground. If it's cold enough, that moisture becomes snow.

Stationary Front

From when the boundary between two air masses stalls. Sometimesan approaching front will stall for several days with warm air on one side of it and cold air on the other side. Cloudy skies and light rain forms.

Air Mass

Large bodies of air that have the uniform temperature, humidity, and pressure. Air masses are responsible for weather patterns. This form when large high-pressure systems linger over an area for several days. As a high-pressure system comes in contact with Earth, the air in the system takes on the temperature and moisture characteristics of the surface below it. Like high- and low-pressure systems, air masses can extend for 1,00km or more. Sometime airmasses cover the whole US. Air masses are classified by their temperature and moisture. Air masses formed over land are called continental air masses, and the ones that form over water are called maritime. Warm air masses are formed near the equatorial regions are called tropical. Those that are formed in cold regions are called polar. The coldest regions of the globe, are called arctic and antarctic air masses. Continental air masses don't have as much moisture as maritime air masses so it continental air masses are drier. Air masses could change when it moves over land or ocean. Warm, moist air could turn into cold, dry, and cold, dry could turn into warm, moist air. The kinds of air masses are arctic air masses, continental polar air masses, maritime polar air masses, continental tropical air masses, and maritime tropical air masses.

Isobar

Lines that connect all places on a map when the pressure has the same value. Isobars show the locations of high and low-pressure systems. When the isobars are close together, the winds are strong. When the isobars are farther apart, the winds are weaker.

Isotherm

Lines that connect places with the same temperature. Isotherms show which areas are warm and which are cold. Fronts are represented as lines with symbols on them.

Occluded Front

Occluded front(blocked front) forms when a fast-moving cold front catches up with a slow-moving war front. Cold fronts are faster than warm fronts. Usually, this front brings precipitation.

Continental Tropical Air Masses

The air mass that forms in the tropics over dry, desert land. Contains hot and dry air and usually forms in the summer. This cloud brings clear skies and high temperatures as its weather.

Arctic Air Masses

The air mass that forms over Siberia and the Arctic. The air it contains is bitterly cold, dry air. During the winter, it can bring the temperature down -40 degrees Celcius.

Continental Polar Air Masses

The air mass that forms over in Canada, and is fast-moving. Contains dry and cold air. Brings cold temperatures in the winter and cool weather in the summer.

Maritime Polar Air Masses

The air mass that forms over the northern Atlantic and Pacific oceans. Contains cold and humid air. Brings cloudy, rainy weather.

Maritime Tropical Air Masses

The air mass that forms over the western Atlantic Ocean, Gulf of Mexico, and the eastern Pacific Ocean. Contains hot, humid air to the southeastern part of the US in the summer. Brings heavy snow fall in the winter.

Humidity

The amount of water vapor in the air. When humidity is high, more water vapor is in the air. High humidity could also cause stickiness, and makes sweat difficult to evaporate. Humidity is measured in grams of water per cubic meter of air(g/m3).

Relative Humidity

The amount of water vapor present in the air compared to the maximum amount of water vapor the air could contain at the temperature. Saturated air holds more water vapor. Temperature determines the maximum storage of water vapor. Warm temperature can contain more than cold temperature. Relative humidity is measured by a psychrometer.

Weather

The atmospheric conditions, along with short-term changes, of a certain place at a certain time. Weather variables are like air temperature, air pressure, wind speed and direction, humidity, relative humidity, dew point, clouds coverage, precipitation. The weather might change in an hour or will last for several days. Temperature and rainfall is part of the weather, but not all.

Air Pressure

The force that a column of air applies on the air or a surface below. Air pressure is high at low altitudes, air pressure is low at high altitudes. A barometer measures air pressure in millibars(mb). barometric refers to air pressure and could be used to predict weather.

Wind Chill Factor

The lowering of body temperature due to the passing flow of lower-temperature air. Wind chill numbers are always lower than the air temperature. Sometimes the weather forecasts will say it feels like something-something, and it is because of wind chill factor that lowers the temperature feeling. It can be warm, but the wind might be colder to lower the temperature in that area.

Water Cycle

The series of natural processes by which water continually moves among oceans, land, and the atmosphere. Precipitation is a big part of the water cycle. Evaporation and condensation are important phase changes in the water cycle. Water vapor is from the oceans' water being evaporated by the sun's energy. Water vapor cools as it reaches the atmosphere then turns into a liquid by condensation. The droplets of liquid condense on particles to form clouds. Precipitation comes from the clouds which allow liquid or solid from the water to arrive on the Earth's surface.

Dew Point

The temperature at which air is saturated and condensation can occur. Temperature decreases in the air mean it can hold less moisture. Air that saturates near the Earth's surface turns into a liquid. When the air becomes saturated, water droplets form. Temperatures above 0 degrees Celcius, dew forms. Temperature below 0 degrees Celcius, ice crystals and frost form. Measured by water vapor in the air(g/m3) in Celcius.

Rain Gauge

The tool that measures precipitation by inches or centimeters.

Psychrometer

The tool that measures the relative humidity of an area. Air with 100% relative humidity means it cannot contain any more moisture and dew or rain will form. Air with half amount of water vapor that it can hold means it is 50% on the scale.

Precipitation

Water, in liquid or solid form, that falls from the atmosphere. Kinds of precipitation are rain, snow, sleet, and hail. Cloud droplets combine to become large enough to become precipitation. Rain- droplets of water. Snow- frozen crystals of water. Sleet- from snow to water to freezing rain. Hail- from small ice to larger ice by updraft to large pellets of ice. Measured using a rain guage by inches or centimeters.