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Mid-latitude Cyclones

Mid-latitude Cyclones. A low pressure system in which the winds flow counterclockwise in the N. Hem. Accompanied by a warm front and a cold front The major weather producer for the U.S. Mid-latitude Cyclones. Figure 18.9 on pg. 502. Lifecycle: 6 stages Formation Wave development

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Mid-latitude Cyclones

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  1. Mid-latitude Cyclones • A low pressure system in which the winds flow counterclockwise in the N. Hem. • Accompanied by a warm front and a cold front • The major weather producer for the U.S.

  2. Mid-latitude Cyclones Figure 18.9 on pg. 502 • Lifecycle: 6 stages • Formation • Wave development • Development of cyclonic flow • Occlusion • Storm intensification • Cyclone dissipation

  3. Cyclogenesis is the formation of a mid-latitude cyclone. Initially, the polar front separates the cold easterlies and the warmer westerlies. As cyclogenesis begins, a “kink” develops along the boundary. The cold air north of the front begins to push southward behind the cold front, and air behind the warm front advances northward, creating a counterclockwise rotation around a weak low-pressure system.

  4. With further intensification, the low pressure deepens even further and distinct warm and cold fronts emerge from the original polar front. Convergence associated with the low pressure can lead to uplift and cloud formation, while linear bands of deeper cloud cover develop along the frontal boundaries. Occlusion represents the end of the cyclone’s life cycle and takes place as the center of the low pressure pulls back from the warm and cold fronts.

  5. The figure depicts the typical structure of a mature cyclone and the processes causing uplift. Shaded areas represent the presence of cloud cover. The numbers represent an approximation of the precipitation probability.

  6. Divergence in the upper atmosphere, caused by decreasing vorticity, draws air upward from the surface and provides a lifting mechanism for the intervening column of air. This can initiate and maintain low-pressure systems at the surface. Conversely, increasing upper-level vorticity leads to convergence and the sinking of air, which creates high pressure at the surface. Surface low-pressure systems resulting from upper-tropospheric motions are called dynamic lows and are distinct from thermallows caused by localized heating of air from below.

  7. NOW LET’S DISCUSS THE WEATHER ASSOCIATED WITH A MID-LAT CYCLONE…PLEASE SEE THE HANDOUT GIVEN.

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