Fronts

Fronts & Lows

Objectives:

1. Describe the weather conditions associated with different types of fronts.

2. Describe the life cycle of a mid-latitude low.

Key Terms:

front cold front warm front occluded front stationary front

Notes: (20-2)

As we stated earlier, weather is constantly changing as different air masses interact with each other around our globe. Nowhere is this seen as much as is in the mid-latitudes where the cold air from the polar regions (cA, cP, & mP) mix with warm air from the equator (mT & cT). The boundary that separate the different air masses is called a front. The following are basic characteristics of a front.

	less dense warm air moves over the more dense cold air
	wedge shaped
	steepness of the slope indicates the severity of the weather
	usually brings clouds and possibly precipitation

Cold Fronts

A cold front is characterized by cold dense air that is advancing on warmer less dense air.

cold air slides under the warm air forcing it upward

the rising warm air quickly condenses as it rises

the type of air in the warm front determines the type of weather (warm saturated air brings thunderstorms)

	cumulous and cumulonimbus clouds
	heavy brief showers

since the advancing front is slowed by friction, cold fronts usually have steep slopes

cold dry weather usually accompanies the passing of the front

Cross-section of a cold front

(www.bom.gov.au/info/ftweather/ images/cold_front.gif)

Warm Fronts

A warm front is characterized by warm less dense air that is advancing on colder dense air.

warm air slides over the cold air

the rising warm air slowly condenses as it rises over the colder air

	cirrus clouds indicate an advancing warm front
	cirrostratus clouds follow is there is sufficient moisture

the type of air in the warm front determines the type of weather

if the warm air is saturated alto and nimbostratus clouds bring prolonged rain showers

warm weather usually follows the front passing

(atschool.eduweb.co.uk/.../ppt/ depression/HTML/img004.gif)

Occluded & Stationary Fronts

occluded fronts occur as the faster moving cold front overtakes the slower moving warm front

can cause clouds and brief precipitation

stationary fronts occur as frontal systems are not moving

associated with flooding

(earth.usc.edu/.../weather/images/ massesfronts/nineten.jpg)

Weather and Pressure Systems

High pressure

	warm days and cold nights
	temperature inversions are likely in this system
	there is little or no wind in the center of the high

Low pressure

	cloudy and cold
	precipitation usually accompanies the passing of the cold and warm fronts

Last modified: January 27, 2005