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Section 6.2 Fronts

NOAA Jetstream:

The boundaries between air masses are known as fronts. Because they divide air masses with different properties, the passage of the front is usually associated with a change in the weather. There are different types of fronts:

  • cold front: colder air follows the front's passage; cold air generally moves faster and underneath warmer air. This usually leads to a relatively abrupt zone of lifting and cumuloform clouds

  • warm front: warmer air follows the front's passage; warm air usually slides over the colder air mass relatively gradually. This leads to a gradual sequence of cloud types and longer-term precipitation.

  • stationary front: little horizontal movement along front

  • occluded front: when a faster-moving (usually cold) front overtakes a slower warm front; a cold occlusion is when the new air mass is more stable than what it is replacing whereas a warm occlusion is when the new air mass is less stable than what it is replacing;

  • dryline: a frontal boundary based upon moisture & wind instead of temperature (e.g., cT and mT air over Texas): huge difference in dewpoint

The movement of fronts is closely tied to general cyclonic and anti-cyclonic circulation patterns. The low-pressure systems in particular can develop into large, strong storms known as mid-latitude cyclones.