Jet Streams, Air Masses, and Weather Fronts Overview

Polar Jet Stream

The polar jet stream is influenced by seasonal factors such as the angle of sunlight, which changes temperature contrasts between the poles and mid-latitudes, pushing it south in winter and north in summer.

Impact of Jet Stream on Weather

The polar jet stream steers low-pressure systems, with a southward dip bringing cold outbreaks and storms, while a northward shift brings warm, stable air.

Jet Streams and Storm Systems

Jet streams form at the polar front where cold and warm air collide, creating instability and strong winds that intensify pressure systems and direct their movement.

Continental Polar Air Mass (cP)

Cold, dry air mass that forms over land, specifically Canada.

Maritime Tropical Air Mass (mT)

Warm, moist air mass that forms over the ocean, specifically the Gulf of Mexico.

Cold Front Passage Sequence

The sequence includes warm, moist air ahead, rising clouds and cumulonimbus formation, possible thunderstorms, a sharp temperature drop, and clear, cooler air behind.

Stationary Front

A stationary front occurs when two air masses stall, resulting in cloudy conditions and light rain for days.

Occluded Front

An occluded front occurs when a cold front overtakes a warm front, leading to mixed precipitation.

Warm Front

A warm front occurs when warm air rises gradually over cold air, resulting in steady rain followed by warming.

Uneven Heating of Earth

Uneven heating causes solar radiation to be most direct at the equator, creating low pressure as warm air rises and high pressure at the poles where cold air sinks, driving convection currents.

Coriolis Effect

The Coriolis Effect causes winds to curve right in the Northern Hemisphere and left in the Southern Hemisphere, resulting in curved wind belts instead of straight flows.

Westerlies

The prevailing Westerlies, found between 30° and 60° latitudes, move west to east and dominate mid-latitudes like the U.S., steering storms and weather systems.

Barometer

A barometer measures air pressure, with rising pressure indicating clear weather and falling pressure indicating storms, making it important for weather forecasting.

Isobars on Weather Maps

Close isobars indicate strong winds, as winds blow from high to low pressure, and they reveal high/low pressure systems used to predict wind directions and storm paths.

Hygrometer

A hygrometer measures humidity; analog versions use hair strands or coils that expand with moisture, while digital versions use sensors to detect water vapor levels.

Ice Core Samples

Ice core samples trap air bubbles containing ancient CO₂ and methane, allowing scientists to analyze gas levels and oxygen isotopes to determine past temperature and atmospheric composition.

Weather vs. Climate

The key difference between weather and climate is that weather refers to short-term atmospheric conditions, while climate refers to long-term averages and trends.

Weather

Short-term (hours/days), variable

Climate

Long-term (decades/centuries), average trends

High-pressure systems

Conditions include sinking air, clear skies, dry weather, and stable conditions.

Falling air pressure

Indicates rising air and cloud formation, making rain or storms likely.

Carbon dioxide (CO₂)

The greenhouse gas that contributes most to warming, released by burning fossil fuels, has a long atmospheric lifespan, and is a major contributor.

Greenhouse effect

Greenhouse gases trap infrared heat in Earth's atmosphere, maintaining warmth; too many gases lead to global warming and alter energy balance.

Major human contributions to climate change

Includes burning fossil fuels, deforestation, industrial emissions, and agriculture.

Acid rain formation

Occurs when sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) from factories and cars mix with water vapor to form sulfuric and nitric acid, which then falls as acid rain.

Environmental effects of acid rain

Includes soil and water acidification, damage to trees, and corrosion of buildings and statues.

Relative humidity calculation

Use dry bulb and wet bulb thermometers; subtract Dry - Wet = depression and use a chart to find relative humidity.

100% relative humidity

Indicates that air is saturated, leading to condensation, cloud formation, and possible precipitation.

Precipitation zones

Precipitation is likely near cold and warm fronts, where warm moist air rises over colder air; low-pressure systems also produce rain.

Weather station model

Shows data such as temperature (top left), wind direction and speed (via flag), cloud cover (center circle), and pressure and precipitation symbols.

Air Mass

A large body of air that has uniform temperature, humidity, and pressure, forming over stable source regions.

Continental air mass (c)

Dry air mass formed over land.

Maritime air mass (m)

Moist air mass formed over water.

Tropical air mass (T)

Warm air mass based on latitude.

Polar air mass (P)

Cold air mass based on latitude.

Arctic air mass (A)

Very cold air mass based on latitude.

cP (Continental Polar)

Cold, dry air mass from the interior of Canada and Alaska; causes clear, cold, stable air and extreme cold in winter.

cA (Continental Arctic)

Very cold, dry air mass from Arctic regions; even colder than cP with bitter cold and clear skies.

mP (Maritime Polar)

Cool, moist air mass from the North Pacific and North Atlantic; causes cloudy, damp, rainy conditions and snow near coastlines.

mT (Maritime Tropical)

Warm, moist air from the Gulf of Mexico, Caribbean, tropical Atlantic & Pacific. Brings thunderstorms and hurricanes.

cT (Continental Tropical)

Hot, dry air from the Desert Southwest (U.S./Mexico). Characterized by dry heat, clear skies, and drought potential. Rare in winter.

Cold Front

A boundary where a cold air mass pushes under a warm air mass, forcing the warm air to rise quickly.

Cold Front Symbol

Blue line with triangles pointing in the direction of movement.

Cold Front Air Movement

Cold air advances; warm air rises rapidly.

Cold Front Clouds

Cumulus to Cumulonimbus.

Cold Front Weather

Brief, heavy rain or snow; thunderstorms; gusty winds.

Cold Front After Front

Cooler, drier air; falling temperatures.

Cold Front Speed

Moves fast (up to 35 mph or more).

Warm Front Symbol

Red line with semicircles pointing in the direction of movement.

Warm Front Air Movement

Warm air rises gently over cold air.

Warm Front Clouds

Cirrus to Altostratus to Nimbostratus.

Warm Front Weather

Steady rain or snow, fog ahead of the front.

Warm Front After Front

Warmer, more humid air.

Warm Front Speed

Moves slowly (10-20 mph).

Stationary Front Symbol

Alternating red semicircles and blue triangles on opposite sides of a line.

Stationary Front Air Movement

Stalled or very slow; both air masses push equally.

Stationary Front Clouds

Stratus or nimbostratus.

Stationary Front Weather

Cloudy, rainy, or snowy for days in the same area.

Stationary Front After Front

Little change until one air mass begins to move.

Stationary Front Speed

Barely moves or moves very slowly.

Occluded Front Symbol

Purple line with alternating triangles and semicircles pointing the same direction.

Occluded Front Air Movement

Cold air pushes underneath both warm and cool air.

Occluded Front Clouds

Mixed: cumulus, stratus, nimbostratus.

Occluded Front Weather

Rain or snow, often widespread and moderate to heavy.

Occluded Front After Front

Cooler air dominates.

Occluded Front Speed

Variable, usually moderate.

Summer Thunderstorm Scenario

cP meets mT at a cold front, leading to violent thunderstorms and sudden cooling.

Winter Ice Storm Scenario

mT overruns cold surface air (cP) at a warm front, resulting in freezing rain and sleet, followed by warming.

Long-lasting Rain Scenario

mP and mT meet and stall at a stationary front, causing days of rain and flooding risk.

Strong Mid-latitude Cyclone Scenario

mT, cP, and mP form an occluded front leading to heavy widespread rain or snow.