1. Weather Fronts

2. Air Masses
Global winds result from large amounts of air moving from high pressure to low.
A large, homogenous parcel of air is called an air mass.
These huge masses of air can cover 100 million hectares from the ground to the tropopause.

3. Types of Air Masses
Air masses are named for two properties of the air in the mass—its temperature and water content.
Dry air masses begin over land masses (continents) and are called continental.
Wet air masses start over oceans and are called maritime (from Latin “of the sea”).
Cold air masses form near the north and south poles, so we call them polar.
Warm air masses come from the tropics and are called tropical.
The four types of air mass are continental polar, continental tropical, maritime polar, and maritime tropical.

4. Fronts
The place where two air masses come together is called a front, because it is often the first part we see of a storm.
A storm front can be dangerous, bringing strong wind, heavy rain, lightning, or tornadoes.

5. Types of Fronts
Fronts are divided into types based on how the air masses are moving.
Each type of front has different line to show it on a weather map.

6. Cold Fronts
When a polar air mass is moving toward a tropical mass, we call it a cold front.
Cold fronts are represented by a blue line with triangles showing which way the front is moving.
Cold fronts push warm air up as they pass causing clouds and storms to form ahead of a cold front.

7. Warm Fronts
When a tropical air mass runs into a polar one, we call it a warm front.
Warm fronts are shown with a red line and semicircles to show the direction of movement.
The warm air is forced up and over the cold air often forming clouds ahead of the front.

8. Stationary Fronts
When polar and tropical air masses pass by each other in opposite directions, we call it a stationary front.
A stationary front is shown by alternating blue triangles and red semicircles.
The weather tends to be milder than with warm or cold fronts, but since the rain is likely to continue for hours or days it can cause flooding.

9. Occluded Fronts
When a tropical mass gets caught between two polar masses, we call it an occluded front.
Occluded fronts are shown by alternating triangles and semicircles in blue or purple.
The warm mass is forced up and over the slower moving cold mass, created cold rains or in winter snow or freezing rain.