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20.2 Fronts and Lows

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Samantha Dieck

on 13 October 2014

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Transcript of 20.2 Fronts and Lows

Fronts and Lows
What is a Front?
Front
: A boundary that separates opposing air masses.
Width can range from 200 meters to 200 kilometers.
Most common at mid-latitudes where polar air masses collide with tropical air masses.
General Guidelines of a Front
Less-dense air mass will be forced up.
Can have steep slopes.
1 over 50 = the frontal surface rises 1 km every 50 km of distance.
Fronts usually bring precipitation.
Warm, less-dense air rises and cools, causing water vapor to condense and form precipitation.
The weather associated with a particular front depends on the types of air masses involved and the speed at which the front is moving.
Kinds of Fronts
Cold Front
Boundary between an advancing
cold air
mass and the
warmer air
mass it is displacing (moving).
Cold air
slides underneath the warm air, forcing the
warm air
up.
Steep slopes (1 over 50)
Weather depends on kinds of air:
Cold cP air
pushes
warm, moist mT
air up and creates thunderstorms.
Cold cP air
pushes hit,
dry cT air up
and creates no precipitation.
Precipitation only covers a narrow band ahead of the front; passes quickly.
*See animation
Types of Fronts
Warm Front
Boundary between an advancing
warm air
mass displacing
cold air
.
The
warm air
rises above the
cold
, causing the
cold air
mass to retreat slowly.
Gradual slope, which causes the weather changes to be more gradual.
Ultimately, steady rain or snow will occur, bringing warmer weather once over.
Thunderstorms are not typical with warm fronts.

Chapter 20 Section 2
Types of Fronts
Occluded Front
When a
cold front
“catches up” to a
warm front
.
Warm air is forced up, cooling and condensing to bring clouds and precipitation.
Types of Fronts
Stationary Front
When a front is not moving forward (it’s stationary).
Warm air rises, cooling and condensing to bring clouds and precipitation.
If it remains stationary for too long, flooding can occur.
Learning Targets
Describe the weather conditions associated with different types of fronts.

Describe the weather associated with low and high pressure systems.
Key Terms
Front
Cold Front
Warm Front
Occluded Front
Stationary Front
High and Low Pressure Systems
The atmosphere exerts air pressure on Earth’s surface.
High Pressure System
Air flow is down and away from the center of the system.
Pressure from above “stops” evaporation (no condensation or precipitation).
Low Pressure System
Air flow is up and away from the center of the system.
Allows evaporation to occur (condensation and precipitation).
Weather Associated with Pressure Systems
Low Pressure
Warm front brings increased cloud formation and a steady rain or snow fall.
As the warm front passes, the temperature warms, winds shift, and the sky may clear.
Cold front beings scattered showers and thunderstorms.
As the cold front passes, the temperature drops, winds shift, and the sky clears.
High Pressure
Clear skies (can lead to hot days and cold nights).
Little to no wind at the center- air masses form here.
Weather Associated with Pressure Systems
1km up every 50km over
1 km up every 300 km over
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