Fronts

Air Mass

In meteorology, an air mass is a large volume of air, defined by its temperature and water vapour content. The temperature and water vapor within an air mass are influenced by the surface the air is moving over.
For example if an airmass is over an ocean, it is likely that the water vapour content will be higher than an air mass over land.
An air mass over Antarctica will be colder than and airmass over a desert in Africa.

Fronts

The word "front" is used to describe what happens when two different air masses meet.

Cold Front A front is "Cold" when a colder air mass is moving towards a warmer air mass
Warm Front A front is "Warm" when a warmer air mass is moving towards a colder air mass
Stationary Front This happens when a cold front and a warm front meet and collide
Occluded Front This happens when a Cold front overtakes a warm front, or when a warm front overtakes a cold front
800px-Example_of_a_cold_front.svg.png 800px-Example_of_a_warm_front.svg.png
This picture shows what happens at a Cold Front (image embedded from Wikipedia on 01 August 2009 ) This picture shows what happens at a Warm Front (image embedded from Wikipedia on 01 August 2009)

Fronts and Associated Weather

The Cold Front

Before and during the passage of the front:

Air pressure
As a cold front approaches the air pressure will decrease
Temperature
The temperature will remain warm until the front passes when there will be an abrupt decrease in temperature
Wind
There can be a sudden change in wind direction as the front passes, and also a strong increase in wind speed
Rain
There will be showers, possibly heavy, and these can include hail
Visibility
Visibility is extremely poor as the front passes.
Humidity
Humidity during the front passage is high.
Cloud
Cloud types associated with a cold front include Cumulous, Cumulo-nimbus and Nimbo-stratus

After the passage of the front:

Air pressure
The air pressure will begin to decrease
Temperature
Colder temperatures will prevail
Wind
Wind speed will slowly decrease
Rain
Showers may cease quickly, then isolated showers
Visibility
Very good visibility
Humidity
Humidity will be lower than before the front passed
Cloud
There may be some residual cloud, possibly isolated Cumulous and Cumulo-nimbus

The Warm Front

Before and during the passage of the front:

Air pressure
As a warm front approaches the air pressure will decrease
Temperature
Temperature will increase as the front passes
Wind
There can be a sudden change in wind direction and the wind speed will increase
Rain
Initially rain will be light, but then will increase to persistent heavy rain
Visibility
Visibility will steadily decrease and become very poor
Humidity
Humidity will increase
Cloud
Cloud types associated with a warm front include Cirrus, Cirro-stratus, Alto-stratus, and Nimbo-Stratus. There may be Cumulo-nimbus as well.

After the passage of the front:

Air pressure
Air pressure will remain constant or increase slightly
Temperature
There will be little change in temperature
Wind
Wind direction and strength will remain steady
Rain
There will be patches of rain and drizzle
Visibility
Visibility will be fair, but poor in rain/drizzle
Humidity
Humidity will remain high
Cloud
Low level cloud may persist

References
1. Wikipedia (2009) Retrieved from http://en.wikipedia.org/wiki/Weather_front during July - August 2009
2. Wagtendonk, W. (2003) Meteorology for Professional Pilots. Bay of Plenty, New Zealand: Aviation Theory Centre (NZ) Ltd.

Want to know more?

Wikipedia
Weather Fronts A page within Wikipedia that goes into more technical depth about all types of frontal systems.
University of Illinois
Fronts, the boundaries between air masses An educational document which describes all types of frontal systems.
MetService, NZ
Weather Map A link to the latest weather map for New Zealand, provided by MetService.

Contributors to this page

Authors / Editors

Flyer_86 does not match any existing user name
JDPerezgonzalezJDPerezgonzalez

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License