Earth & Space Science Chapter 14: Air Masses

Questions and Answers

What is a common factor in the formation of all thunderstorms?

Cold, dry air

Low atmospheric pressure

Unequal heating of the Earth's surface

Warm, moist air (correct)

What is the main reason why thunderstorms are common in the afternoon and early evening?

Buoyancy and instability are enhanced by high surface temperatures (correct)

Downdrafts are more prevalent during this time

There is a continual supply of warm, moist air available

Surface heating is sufficient to grow a towering cumulonimbus cloud

What is the typical lifespan of a single cumulonimbus cloud within a thunderstorm complex?

Days

1 hour (correct)

10-15 minutes

Several hours

What is the name given to thunderstorms that produce high winds, damaging hail, flash floods, and tornadoes?

Severe thunderstorms Signup and view all the answers

What is the estimated number of thunderstorms that occur on Earth at any given time?

2,000 Signup and view all the answers

What is the typical diameter of suction vortices within a strong tornado?

30 feet Signup and view all the answers

What is the typical speed of updrafts in thunderstorms?

40-60 mph Signup and view all the answers

What percentage of thunderstorms produce tornadoes?

1% Signup and view all the answers

What is the main factor that contributes to the development of downdrafts in thunderstorms?

Cooling effect of falling precipitation Signup and view all the answers

What is the estimated number of thunderstorms that occur in the US each year?

100,000 Signup and view all the answers

What is the typical size of a mesocyclone?

2-6 miles across Signup and view all the answers

Where are tornadoes most likely to occur in the United States?

Central US Signup and view all the answers

What is the term used to describe the rotating column of air in a tornado?

Vortex Signup and view all the answers

What is the average speed of a tornado?

30 mph Signup and view all the answers

What is the estimated maximum wind speed in a tornado?

300 mph Signup and view all the answers

What is the direction that most tornadoes travel?

Northeast Signup and view all the answers

What is the average width of a tornado?

330 feet Signup and view all the answers

What is the typical wind speed of a weak tornado?

90 mph Signup and view all the answers

What is the maximum wind speed of an extremely violent tornado?

310 mph Signup and view all the answers

In which months are tornadoes most frequent?

April, May, June Signup and view all the answers

What is a major factor in the destruction caused by a tornado?

The wind speed Signup and view all the answers

What percentage of tornadoes are classified as EF-4 and EF-5?

2% Signup and view all the answers

What is the primary purpose of the Storm Prediction Center (SPC)?

To provide accurate and timely forecasts for severe thunderstorms and tornadoes Signup and view all the answers

What is the typical time interval for a tornado watch?

4 to 6 hours Signup and view all the answers

What is the area typically covered by a tornado watch?

25,000 mi2 Signup and view all the answers

What is the primary reason for issuing a tornado warning?

When a tornado has actually been sighted or is indicated by radar Signup and view all the answers

What is the typical duration of a tornado warning?

30 minutes to 1 hour Signup and view all the answers

Why are tornadoes difficult to forecast?

Because they are short-lived and don't last very long Signup and view all the answers

What is the result of advances in technology, communication, and improved forecasts?

A significant decline in tornado deaths Signup and view all the answers

What is the purpose of the Enhanced Fujita Intensity Scale (EF-Scale)?

To classify storms by assessing the damage produced Signup and view all the answers

What is the minimum water temperature required for hurricane formation?

80° F Signup and view all the answers

Why do hurricanes not form within 5° of the equator?

The Coriolis effect is too weak Signup and view all the answers

What is the term used to describe a tropical system with sustained wind speeds of less than 38 mph?

Tropical depression Signup and view all the answers

What is the main factor that determines the amount of damage caused by a hurricane?

Strength of the storm Signup and view all the answers

What is the name of the scale that ranks hurricanes based on their relative intensities?

Saffir-Simpson scale Signup and view all the answers

What happens to a hurricane when it moves over water that cannot supply warm, tropical air?

It weakens Signup and view all the answers

What is the term used to describe the rotation of a hurricane?

Cyclonic circulation Signup and view all the answers

What happens to the air density in a tropical disturbance when significant latent heat is released?

It decreases Signup and view all the answers

How many storms achieve tropical storm strength each year on average?

Between 80 and 100 Signup and view all the answers

What is the term used to describe the diverging air in the upper layers of a hurricane?

Outflow Signup and view all the answers

What is the typical width of a storm surge?

40 to 50 miles Signup and view all the answers

What is the most intense side of the eye in the Northern Hemisphere?

Right side Signup and view all the answers

What type of structures are particularly susceptible to wind damage?

Mobile homes Signup and view all the answers

What can hurricanes also spawn?

Tornadoes Signup and view all the answers

What is the goal of monitoring and forecasting tropical system movement and intensity?

To provide timely watches and warnings Signup and view all the answers

Why are storm surges worse where the continental shelf is very shallow and gently sloping?

Because the water is shallower Signup and view all the answers

What can heavy rains and inland flooding affect?

Areas hundreds of miles from the coast Signup and view all the answers

What is used to monitor and forecast tropical system movement and intensity?

Satellite data, aircraft reconnaissance, coastal radar, and remote buoys Signup and view all the answers

Why are hurricane watches and warnings still issued for relatively large coastal areas?

To protect lives Signup and view all the answers

What is the term used to describe the rotating column of air in a tornado?

Mesocyclone Signup and view all the answers

What denotes the characteristic properties of an air mass?

Humidity and temperature Signup and view all the answers

Which type of air mass originates over land and is typically dry?

Continental Tropical Signup and view all the answers

How are air masses categorized based on their characteristics?

By their source area and surface nature Signup and view all the answers

What is the typical temperature characteristic of an Arctic air mass?

Very cold Signup and view all the answers

Which scenario is most likely associated with Continental Polar air masses?

Snowstorms in fall and winter Signup and view all the answers

What defines a Continental Arctic air mass?

Originates in high latitudes and is dry Signup and view all the answers

Which region is most affected by lake-effect snows caused by Continental Polar air masses?

Buffalo and Rochester, NY Signup and view all the answers

What type of air mass is typically humid and originates over water?

Maritime Polar Signup and view all the answers

Which type of air mass is primarily responsible for the precipitation received by the eastern two-thirds of the United States?

Maritime Tropical (mT) Signup and view all the answers

What characterizes a warm front?

Small slope and light-to-moderate precipitation Signup and view all the answers

What happens when two air masses clash at a front?

The warmer air mass is forced aloft Signup and view all the answers

Which front is represented on a weather map with blue triangles extending into warmer air?

Cold Front Signup and view all the answers

What is the pressure gradient effect at a front?

Results in one air mass moving faster than the other Signup and view all the answers

Which type of front does NOT move?

Stationary Front Signup and view all the answers

What type of front occurs when a cold front overtakes a warm front?

Occluded Front Signup and view all the answers

Where do midlatitude cyclones primarily develop?

Along a front where air masses are parallel Signup and view all the answers

What is indicated by the 'L' symbol on a weather map?

Low-pressure center Signup and view all the answers

What is necessary for a tropical system to be classified as a hurricane?

Sustained winds in excess of 74 mph Signup and view all the answers

Which feature surrounding a hurricane's center experiences the highest winds and heaviest precipitation?

The eye wall Signup and view all the answers

What is the primary energy source for hurricanes?

Latent heat released from forming clouds Signup and view all the answers

What role does Doppler radar play in tornado detection?

It enhances the accuracy of tornado warnings through motion detection. Signup and view all the answers

Which of the following is true regarding the eye of a hurricane?

It is typically around 12.5 miles in diameter. Signup and view all the answers

Which of the following best describes hurricanes compared to mid-latitude systems?

They do not require fronts for formation. Signup and view all the answers

What is the lowest recorded pressure in an Atlantic basin hurricane?

882 millibars Signup and view all the answers

How does air pressure change from the outer edge of a hurricane to its center?

It drops from 1010 millibars to 950 millibars. Signup and view all the answers

Identifying tropical cyclones often requires knowledge of their geographical naming conventions. What is a hurricane known as in the western Pacific?

Typhoon Signup and view all the answers

What is a common consequence of the most powerful hurricanes?

They often cause significant loss of life and financial devastation. Signup and view all the answers

What is the average diameter of a mid-latitude cyclone?

1,000 miles Signup and view all the answers

What is the typical wind direction after the passage of a cold front?

Northerly Signup and view all the answers

What type of air mass is associated with air-mass thunderstorms?

Maritime tropical Signup and view all the answers

Which of the following is NOT a characteristic of a mid-latitude cyclone?

Surface divergence Signup and view all the answers

Which of the following is NOT a characteristic of a thunderstorm?

Strong inward spiral of wind Signup and view all the answers

What happens to the warm sector of a mid-latitude cyclone as the cold front catches up to the warm front?

The warm sector is lifted aloft Signup and view all the answers

What is the primary factor that drives the development of mid-latitude cyclones?

Upper-level air flow Signup and view all the answers

What are the typical weather conditions associated with a warm front?

Light precipitation, southerly winds, and warmer temperatures Signup and view all the answers

How do mid-latitude cyclones typically move across the United States?

From west to east Signup and view all the answers

What is the primary difference between a thunderstorm and a mid-latitude cyclone?

Thunderstorms have strong updrafts and downdrafts, while mid-latitude cyclones have a consistent inward spiral of wind Signup and view all the answers

Study Notes

Air Masses

Air masses are vast bodies of air (typically 1000 miles across) with uniform temperature and moisture at given altitudes.
Small variations exist within air masses due to their extensive latitudinal reach (up to 20°).
A source area is where an air mass gains its temperature and moisture characteristics.
Air masses are classified by origin:
- Arctic (A): Very cold, from high latitudes.
- Polar (P): Cold, from high latitudes.
- Tropical (T): Warm, from low latitudes.
Surface nature classification:
- Continental (c): Formed over land, usually dry.
- Maritime (m): Formed over water, usually humid.
Five primary air mass types:
- Continental Arctic (cA): Very cold, from northern Canada.
- Continental Polar (cP): Cold, from northern Canada and Alaska.
- Continental Tropical (cT): Warm, from the Southwestern U.S. and Mexico.
- Maritime Polar (mP): Develops from chilled Siberian air and North Atlantic.
- Maritime Tropical (mT): Source of most eastern U.S. precipitation, comes from warm waters.

Fronts

Fronts are boundaries separating air masses of differing densities, often characterized by temperature and moisture differences.
Typically relatively narrow (9 to 120 miles wide) with low-angle slopes at the frontal surface.
Four types of fronts:
- Warm Fronts: Warm air replaces cold air; slower-moving with light-to-moderate precipitation.
- Cold Fronts: Cold air advances; features heavier and more violent weather, moves faster than warm fronts.
- Stationary Fronts: Both air masses flow parallel to the front with no movement.
- Occluded Fronts: Cold fronts overtake warm fronts, causing complex weather patterns.

Midlatitude Cyclones

Major weather systems between southern Florida and Alaska indicated by an "L" on weather maps.
Form where air masses move parallel and opposite to a front, typically containing cP air north and mT air south.
Development follows these stages:
- Frontal surface shapes to a wave, low pressure at the apex.
- Counterclockwise cyclonic circulation occurs.
- A warm front and cold front form, with the cold front eventually occluding the warm front.
Move eastward across the U.S., causing significant weather contrasts, especially in spring.
Weather changes observed with warm front approach include lower clouds and light precipitation; cold front brings heavy precipitation and potential severe storms.

Thunderstorms

Defined as storms producing lightning, thunder, gusty winds, heavy rainfall, and hail.
Formed from warm, moist air rising in unstable environments, categorized into:
- Air-mass thunderstorms: Typically short-lived; form on warm summer days.
- Severe thunderstorms: Associated with lifting air along fronts; can produce high winds and tornadoes.
Approximately 2,000 thunderstorms occur globally at any given time; the U.S. averages over 100,000 annually.
Required conditions for storms include warm, moist air and ongoing supply from the ground.

Tornadoes

Violent windstorms characterized as rotating columns of air, with pressure in the storm lower than surroundings.
Max wind speeds can exceed 300 mph.
Form in severe thunderstorms, particularly supercells with strong updrafts.
In the U.S. (1992-2002), an average of 57 fatalities per year; notable spikes in severe tornado events like April 2011.
Tornado characteristics include:
- Average diameter of 500 to 2,000 feet, traveling at ~30 mph with a lifespan around 6 minutes.
- Most common in the central U.S., particularly during spring when contrasting air masses collide.
Severe tornadoes may last over 3 hours and can exceed 90 miles in length, causing significant destruction.### Tornadoes
Tornado destruction correlated with wind speed; can propel objects like straw through wood.
Urban areas face significant damage due to population density and wind speed.
Enhanced Fujita Intensity Scale (EF-Scale) classifies tornadoes based on damage, not direct wind speed.
Most tornado fatalities are due to flying debris; less than 2% of tornadoes result in fatalities.
63% of tornadoes rated EF-0 or EF-1, whereas only 2% are EF-4 or EF-5, which account for 70% of deaths.
Tornadoes are difficult to forecast due to their short lifespan; watches and warnings are crucial for safety.
The Storm Prediction Center (SPC) issues multiple severe weather outlooks daily, assessing storm risk.
Tornado watches cover approx. 25,000 square miles for 4-6 hours when conditions are favorable for tornadoes.
Tornado warnings are localized alerts issued when a tornado is sighted or indicated, typically lasting 30 minutes to 1 hour.
Doppler radar enhances tornado tracking, detecting precipitation and wind motion; however, not all tornadoes show clear radar signatures.

Hurricanes

Hurricanes are low-pressure systems forming over tropical waters, requiring sustained winds of 74 mph or more.
Energy for hurricanes comes from latent heat released during cumulonimbus cloud formation.
Most hurricane-related fatalities are from powerful storms like Katrina (2005) and Sandy (2012).
Typically form between 5° and 20° latitudes, with names varying by region: typhoons (Western Pacific) and cyclones (Indian Ocean).
Classification as a hurricane requires sustained winds > 74 mph; hurricanes average 375 miles across.
Central pressure can drop from 1010 to 950 millibars, with Hurricane Wilma holding the lowest recorded Atlantic pressure.
The eye wall, formed by rising warm moist air, has the highest winds; the eye, around 12.5 miles in diameter, exhibits lighter conditions.
Stronger hurricanes develop in warm waters (≥ 80°F) and generally do not form close to the equator due to weak Coriolis effect.
Development stages include tropical disturbances, tropical depressions (≤ 38 mph), and tropical storms (38-74 mph).
Saffir-Simpson scale ranks hurricanes from Category 1 to Category 5 based on intensity, with Category 5 being rare.

Hurricane Damage

Damage is categorized into storm surge (causing most deaths), wind damage, and heavy rains/inland flooding.
Storm surge can extend 40-50 miles and is most severe on the right side of the storm; it dramatically increases in shallow continental shelf areas.
Wind damage results in projectiles and particularly affects mobile homes and high-rise buildings.
Hurricanes can spawn tornadoes, with over half producing at least one upon landfall.
Modern meteorology utilizes satellites, aircraft, coastal radar, and computer models to forecast hurricane movements and provide timely warnings.
Improved track forecasts are vital for assessing storm characteristics and enhancing safety measures.

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Description

Learn about air masses, characterized by similar temperature and moisture at any given altitude, and how they affect weather patterns and severe weather.