Weather Fronts

Fronts

A front is a boundary between two different air masses
Fronts are located on the edge of a transitional zone
Fronts are named for the faster-advancing air mass

Types of Fronts

1. Cold Front

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The colder air mass replaces the warmer air
Denoted by blue triangles pointing toward the direction of movement
Unstable air ahead
- - Vertically developing clouds
Atmospheric pressure will rise after frontal passage
With a cold front, precipitation is along/ahead of the front

Image Description: Cold front - image showing colder air behind the cold front and warmer air ahead of the cold front. Winds are perpendicular to each other and are converging. Warmer air is shown rising above the colder air. Just behind the front, there is precipitation and a cumulonimbus cloud.

2. Warm Front

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The warmer air mass replaces the colder air
Denoted by red half-circles pointing in the direction of movement
Atmospheric pressure will fall after frontal passage
Precipitation is often ahead of the warm front and can include freezing precipitation (see right)
Once the front has moved through, you are now in the warm sector with clear skies

Image description: Warm front - The warmer air is shown blowing towards the colder air and rises above it. Just ahead of the warm front there is fog, then stratus, then Nimbostratus, then higher altitude clouds (cirrus). Note: The cold air is receding from the warmer air.

Image Description: Warm fronts and winter precipitation: NWS image showing warm air (air above freezing) and how it effects frozen precipitation. From left to right: snow is present where there is no warm air ; sleet is present where there is a small region of warm air ; freezing rain is present where there is a large region of warm air ; rain is present where the warm air extends through the surface.

3. Stationary Front

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A boundary between two air masses that are nearly stationary due to the winds being parallel to each other on either side of the front
Denoted by a combination of red half-circles and blue triangles on opposite sides of the line
Cloud development and precipitation on the cold side of the front
During winter, could have a mix of precipitation types

Image Description: Stationary Front 1 - Small visual showing a warm air mass on one side of the stationary front (this side has the red half-circles), and a cold air mass on the other side (shown by the blue trianbles. The winds associated with these air masses are flowing parallel but in opposite direction.

Image Description: Stationary Fronts 2 - Television example of how a stationary front would appear. The cold air mass is behind the blue triangles, while the warm air mass is behind the red half-circles. The triangles and half circles make up the same line. The cold air mass is moving towards the northeast, while the warm air mass is moving towards the southwest (parallel but opposite winds)

4. Occluded Front

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This front will separate air behind the cold front from air ahead of the warm front when the two fronts meet
Denoted by purple half-circles and triangles all pointing in the direction of movement
Cold occlusion: colder air taking over warmer air
Warm occlusion: warmer air taking over colder air

Image Description: Occluded Fronts - the bottom southwest corner of the image shows an advancing cold front moving northeast. There is warm air moving north northeast. Where these fronts meet, and where the colder air is taking over the warmer air, there is an occluded front.

Winds around fronts

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Winds behind a cold, warm, and occluded front are perpendicular to the winds ahead of the front
Winds around a stationary front are typically parallel but opposite

Image Description: Example of cold, warm, stationary and occluded fronts - To the top left is the cold front. To the top right is a warm front. and to the bottom right is an occluded front. This image shows wind arrows behind the fronts blowing perpendicular to the winds ahead of the front. To take away from this image, winds behind the warm, cold and occluded fronts will be perpendicular to the winds ahead of the front. To the bottom left there is a stationary front. Winds associated with a stationary fronts are parallel, but opposite on either side of the front.

Review Surface Station Plots Here!

Identifying Fronts Practice!

Image Description: Identifying air masses/fronts - The blue box is located over the Dakotas and parts of surrounding states. The blue box has encompassed temperatures of 18, 8, and 15. There is a wind barb with two long sticks coming from about 290 degrees. The blue line begins in Western Minnesota (within the blue box), extends through Nebraska, and ends in north central Kansas. The red box surrounds the Great Lakes and Ohio Valley regions, as well as parts of surrounding states. The red box has encompassed temperatures of 32, 46, 35, 41, 48, 40, 41, 34, and 36. The red box has a wind barb with two long sticks coming from about 190 degrees. All temperatures are in degrees Fahrenheit.

The blue box would represent the area behind the cold front, most easily noted by the very cold temperatures and wind direction from the NW (most likely cP air mass).

The blue line represents the cold front itself.

The red box represents ahead of the cold front, noted by the (relatively) warm temperatures and wind direction from the south (most likely an mT air mass).

What type of air mass would be indicated by the blue box?

What does the blue line represent?

What type of air mass would be indicated by the red box?

The Answer is collapsed in the image below

Hint: Look at the wind direction, and think about the source region of the air. The temperatures should help as well.

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