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What is an air mass?
A large body of air that has essentially uniform temperature and moisture conditions
How are air masses named?
According to their moisture content, location and temperature
What type of air masses are stable? Unstable?
- Warm: stable
- Cold: unstable
What is a front?
An area of discontinuity that forms between two adjacent contrasting air masses
The point where a front comes in contact with the ground
Area that encompasses the weather on either side of the front
- Fronts are always located in a trough of low pressure
- Cold fronts generally move faster than warm fronts
- Frontal passage usually is accompanied by a 90° shift in wind direction
What is the slope of the front?
The ratio of vertical rise to horizontal distance
Shallow frontal slopes:
produce extensive cloudiness with steady precipitation
- Move rapidly, narrow bands of cloudiness and showery precipitation
- Normally separate air masses of vastly different properties, indicating more severe weather
How does the speed of frontal movement affect the weather associated with it?
- Faster fronts are accompanied by a narrow band of more severe weather
- Slower fronts, less severe weather but frontal zone is more extensive
How does the contrast between temperature and moisture between two air masses affect the associated weather?
Greater the contrast more severe the weather
What is a cold front?
- The leading edge of a cold air mass.
- Overtaking cold air is more dense than warm air, wedging under a less dense warm air mass which produces unstable conditions
- Thunderstorms, severe turbulence
- Wind shift SW to NW
What is a squall line?
- A line of violent thunderstorms.
- Dashed double dotted purple line
- Develop 50-300 miles ahead of cold front, and parallel to it
What is a warm front?
- The boundary of an advancing warm air mass that is overtaking and replacing a colder air mass
- Warm less dense air rides up over the top of cold air
- Creates a broad area of cloudiness, steady precipitation, reduced visibility, 500-700 miles ahead
- Wind shift SE to SW
What is a stationary front?
- The frontal border between air masses shows little or no movement, with neither air mass replacing the other.
- Alternating cold/warm front symbols pointing in opposite directions
- Winds parallel both sides of the front, 180° wind shift
- Same conditions as warm front but less intense
What is an occluded front?
- Faster moving cold front overtakes a slower moving warm front
- Two types: cold and warm
- Type depends on which front remains in contact with the ground
- Warm/cold symbols pointed in the same direction, colored purple
- 180° wind shift
Where is the most severe weather generally located in an occluded front?
100 south to 300 miles north of the frontal intersection
What is an inactive front?
- Fronts in which clouds and precipitation are not present
- Shown on weather charts to indicate the boundary of the opposing air masses