Chapter 7 Air Masses and Weather Systems

What are the five air masses that affect North America?

- mP (Maritime Polar) from BOTH the North Atlantic (Eastt) and North Pacific (West) Oceans -mT (Maritime Tropical) from BOTH the South Atlantic and South Pacific Oceans -cT (Continental Tropical) from the Gulf of Mexico in the summer time -cP (Continental Polar) from Canada cA (Continental Arctic)

what percentage of the remaining tornadoes spawn from tropical cyclones (tropical storms + hurricanes)?

20%

what percentage of tornadoes are associated with thunderstorms and mid latitude cyclones?

80%.

Dryline

A boundary that separates warm, dry air from warm, moist air. It usually represents a zone of instability along which thunderstorms form. cT air from Mexico and Texas meets with mT air from the Gulf of Mexico. Here the denser drier air lifts the moist mT air over it.

What is a front? How do they develop?

A front is the leading edge of an air mass. The boundary between two different air masses. They occur when the air mass begins to move and encounter a different air mass

* What is a front? How do they develop?

A front is the leading edge of an air mass. They occur when the air mass begins to move and encounter a different air mass.

How are air masses designated?

Air masses are designated by a two letter code that refers to their source region. The first letter is m or c written in lowercase and refers to the humidity characteristics of an air mass. The second letter is capitalized and refers to the source regions latitudinal zone and temperature characteristics.

* Why are air masses classified by whether they develop over land or water?

Air masses originating over land (c) are dry, while air masses positioned over the sea (m) are humid. They are identified by their moisture content.

What are the second letters and descriptions?

E: stands for equatorial air that is very warm or hot T: stands for tropical and is marked by warm air P: Polar, air that can be quite cold A: Arctic, air that is extremely cold AA: Abbreviation for Antarctic air, extremely cold air

mE (maritime equatorial)

Equatorial air masses develop near the Equator, and are warm and humid.

cA (continental arctic)

Extremely cold, very dry, stable. Occasionally impacts the United States in winter with record low temperatures

what are storm surges?

High seas that are pushed onshore from strong winds. Can flood and destroy coastal communities. Most serious hazard.

Where do hurricanes form and develop?

Hurricanes form and develop over the warm, tropical oceans, but are steered by pressure and wind systems toward the midlatitudes.

What is an Air Mass?

Large body of air that is relatively homogenous in temperature and humidity. The characteristics, locations, and movements of an air mass have a significant impact on the weather.

* Do all areas on Earth produce air masses? Why or why not?

No. There are regions on Earth that are a mixture of land and water, like the Great Lakes region of North American which violate the rule of source region homogeneity

* What kind of air mass forms over the Southwestern part of the United States in the summer? What weather conditions are associated with this air mass?

The Southwestern U.S. would experience cT air. The weather associated with a cT air mass is usually hot and dry.

Source Region

The area where an air mass originates.

* What letter symbols are used to identify air masses? How are these combined? What air masses influence the weather of North America? Where and at what time of the year are they most effective?

The letters used for moisture (humidity) are c (continental) and m (maritime). The letters used for temperature are T (tropical), P (polar), A (arctic), and E (equatorial).

What can make an air mass stable or unstable?

This gain or loss of thermal energy, humidity, or both can either make an air mass more stable or cause it to become unstable. If an air mass is colder than the surface it passes over, heat will flow from the land or water surface TO the air mass. For example, an mT air mass that originated from the Gulf of Mexico and moves onshore over a hot land surface in the summer will warm further, possibly becoming unstable and producing heavy convective precipitation.

How is a cyclone shaped?

a cyclone is shaped like a basin. winds converging toward the center of a cyclone will move rapidly if the pressure gradient is great.

what is a squall line?

a line of severe thunderstorms that form along or ahead of a cold front. A squall line can bring strong damaging winds, heavy rain, sometimes hail and possibly tornadoes.

What is a cyclone?

a low pressure area that is typified by uplifting air and winds that tend to converge on the center of the low in an attempt to equalize pressure.

What is a Hurricane?

a massive rotating, cyclonic system with strong low pressure, wind speeds above 73 mph (118 kilometers) and a diameter of 100-400 mi (160-640 kilometers). The extremely low pressure at the center of a hurricane, combined with very strong pressure gradients, produces powerful high velocity winds.

What is a tornado outbreak?

a series of tornadoes spawned by a group of storms

what is a blizzard?

a severe snowstorm with high winds and low visibility.

Nor'easter

a storm or wind blowing from the northeast, especially in New England. Cyclonic winds bring it in.

Convergent uplift/ cyclonic uplift?

air flows toward the center of a low pressure system, it feeds air into an upward spiral of air which can produce clouds and precipitation.

lake effect snow

cP (Continental Polar) or cA (Continental Arctic) moving over the Great Lakes in winter, picks up moisture, and can lead to lake effect snow

Enhanced Fujita Scale

classifies the intensity of a tornado, based on wind speeds and specifically on the types of damage that occur on a scale ranging from eF1 to eF5

what type of weather are occlusions accompanied by?

cloudy, overcast conditions, light rain or snow.

cP (continental polar)

cold, dry, and stable resulting in clear cold weather. Freezing conditions in Texas and Florida

what are thunderstorms?

common storms of the middle and lower latitudes. very simply thunderstorms are atmospheric disturbances that are accompanied by rain, thunder, and lightning.

What are storm tracks?

cyclones or anticyclones following along a similar path called storm tracks.

mP (maritime polar)

damp and cool. move with the westerly atmospheric circulation. Most air developed over the Atlantic does not affect the US. When an mP air is uplifted by overriding a mass of colder, denser air, or a mountain range, cloudy weather and precipitation usually yields snow during the winter in inland regions and higher elevation areas.

cT (continental tropical)

dry and warm. The typical weather associated with a cT air mass is hot and dry, with clear skies and strong solar heating during the daytime. The Sahara Desert and the interior desert region of central Australia are prime examples of source regions for this air mass.

what can be a product of thunderstorms?

hail. when the vertical updrafts of the cells are strong enough to repeatedly carry water droplet into a freezing layer of air that supports pellets of ice.

What is a dopplar radar?

improves tornado detection and forecasting significantly. It is able to measure wind speeds and its direction from the radar site.

The cyclones and anticyclones are steered along paths influenced by what?

influenced by the upper air westerlies

What are the seven air mass types?

mE (Maritime equatorial) mT (Maritime Tropical) cT (Continental Tropical) cP (Continental Polar) mP (Maritime Polar) cA (Continental Arctic) cAA (Continental Antarctic)

What is lightning?

massive discharge of electricity within clouds or between clouds and the ground. Lightning is produced when strong positive and negative electrical charges are generated within a cloud.

what is weather forecasting?

observations made, collected, and mapped to depict the current state of the atmosphere. movement, growth, and decay of weather systems predicted.

What do occlusions represent?

occlusions represent the dissipation of a midlatitude cyclone

cold front

occurs when a cold air mass overtakes a warm air mass, pushing the warm air upwards.

frontal uplift

rising of warm air masses where they meet relatively cold air masses. major source of precipitation.

What is a tornado?

small, intense cyclone with extremely low pressure, strong converging winds and violent winds. They are the most violent storms on earth.

When does temperature and humidity change with air masses?

temperature and humidity changes occur as the air mass gains or loses thermal energy or moisture by interacting with land masses or bodies of water.

(c) Continental

the air mass originated land and is relatively dry.

(m) Maritime

the air mass originated over water and is relatively moist.

warm front

the boundary of an advancing mass of warm air, in particular the leading edge of the warm sector of a low-pressure system. They are slower so there are less abrupt changes. A warm front may bring cloud cover with light and steady precipitation followed by milder temperatures.

what is the calmest and clearest part of a hurricane called?

the eye

Process for thunder?

the heated air (45,000°F+) expands near instantaneously and explosively, creating the sonic shock wave we call thunder.

what do thunderstorms result from?

thunderstorms result from the strong, rapid uplift of moist air and their intensity depends on the degree of instability of the air and the amount of water vapor it holds.

Saffir-Simpson Scale

used to classify hurricane intensity and potential damage by assigning a category from 1-5 based on sustained wind speeds.

mT (maritime tropical)

warm and humid (moisture). The gulf of Mexico and the subtropical areas of the Atlantic and Pacific Oceans are source regions for mT air masses. When mT air masses move inland, the high temperature of the land results in convective uplift that causes precipitation and strong thunderstorms on hot, humid days. Frontal lifting occurs as warm air clashes with cold air Pacific mT cooler and more stable

What is an occluded front?

when a cold front overtakes a warm front and uplifts the warm front abruptly.

What is a stationary front?

when a warm air mass and a cold air mass meet and no movement occurs. neither air mass is strong enough to move the other.

What is a snowstorm?

when frozen precipitation falls as snow.

Fujita Scale

wind velocity for tornadoes

Is a hurricane a single air mass?

yes

Does an air mass typically retain its characteristics as it moves?

yes, as an air mass moves over the Earth's surface it generally retains its distinct characteristics.

Has weather forecasting gotten easier? If so, from what?

yes. -computer technology allows for rapid processing and mapping. can also process numerical data and generate predictions of weather based on data -satellite imaging

* Compare warm and cold fronts. How do they differ in duration and precipitation characteristics?

•. In general, cold fronts can produce short duration but higher intensity precipitation and possible severe storms. Warm fronts may produce long duration but less intense precipitation.

* What is an air mass?

•An air mass is a large body of air with distinguishable characteristics of temperature and moisture (humidity).