Ch 9 : Fronts

Students will be able to: • Identify and define fronts on a weather map

• Draw fronts on a weather map using surface

weather data.

Fronts

• The boundary between two air masses is

called a front

• A front is where the temperature, humidity,

and winds change.

• The triangles or half circles point in the

direction the front or air mass is moving.

• 5 kinds of fronts:

1) Cold Front

• Cold air is advancing and displacing warmer air.

• Has a steeper slope than a warm front causing vigorous upward air motion

• Moves faster than a warm front

• Best chances for thunderstorms (Cumulonimbus)and heavy rains are ahead and along the front

Cold Front

2) Warm Front

• Warm air is pushing ahead and displacing colder air

• Lifting of air is more gentler than along a cold front

• Affects the weather long before the arrival of the rains

– High clouds, middle, and low clouds spread over a large area.

• Steady and wide spread rains or snows

• Thunderstorms are less typical

Warm Front

• http://www.classzone.com/books/earth_science/terc/content/visualizations/es2002/es2002page01.cfm?chapter_no=visualization

3) Stationary Front

• The front does not

move

• Several days of

cloudy and wet

weather

4) Occluded Fronts

• When a cold front overtakes a warm front

• Signals the weakening of a storm

5) Dry Line • A dry line is a boundary that

separates a moist air mass from a dry air mass.

• Also called a "Dew Point Front", sharp changes in dew point temperature can be observed across a dry line.

• Dry lines are most commonly found just east of the Rocky Mountains, separating a warm moist air mass to the east from a hot dry air mass to the west.

Dry Line

• Imagine that you are located at El Paso, Texas on the map. 1. As the cold front approaches, what changes in the sky condition do you expect? 2. What changes in wind direction will occur as the front passes? 3. At the time the front passes what change in temperature will occur?

• Imagine that you are located at New York City, New York on the map. 4. What changes will occur in the sky condition prior to the arrival of the warm front? 5. As the warm front passes, what changes do you expect in wind direction? 6. After the front passes, what changes in weather do you predict?

*An important note! In general, warm fronts are more difficult to discern than cold fronts. Their transition zones are typically much larger and their affects much more widespread.

Label your fronts

Color red where you would expect the warmest

temperatures to occur.

The warmest temperatures are found in the warm air mass that

lies behind the warm front and ahead of the cold front.

mT

Color blue where you would expect to find the coolest

temperatures.

The coolest temperatures are found in the cold air

mass that lies behind the cold front.

cP

Where you would expect the highest wind speeds to

occur?

Where you would expect the highest wind speeds to

occur?

X X

X

Where you would expect to find fair or nice weather?

The highest atmospheric pressure is found at the center of

a high pressure system, labeled with a capital H on a

weather map. Nice weather is associated with it.

Sunny

Where you would expect to find clouds and

precipitation?

The lowest atmospheric pressure is found at the center of a

low pressure system, labeled with a capital L on a weather

map. Rainy weather is associated with it.

Precipitation

Where else would you expect precipitation to occur?

Precipitation typically occurs along and ahead of the

warm front, along the cold front, and around the center

of a low pressure system.

Precipitation

Where would you expect thunderstorms?

Thunderstorms occur most likely next to cold fronts

and dry lines.

Precipitation