15.7. Precipitation

Not only does a mid-latitude cyclone potentially bring great changes in temperature for a region, it can also produce copious amounts of precipitation. Depending on your location within the cyclone’s path comes a variety of different precipitation characteristics. Not only the amount of precipitation that falls, but the way it falls will determine whether it is beneficial or detrimental to an area.

Before we can get precipitation associated with a mid-latitude cyclone we must first get clouds. There are three main components needed to get cloud formation: (1) cloud condensation nuclei (CCN), (2) a source of moisture, and (3) a source of lift. Generally, there is always plenty of CCN, but without ample moisture, no amount of lift will allow a parcel of air to reach saturation and thus form a cloud.

For precipitation we need these cloud formation processes to continue for some time, such that the droplets (or ice crystals) within our clouds continue to grow. This usually requires added moisture and more lift. The main source of moisture for weather systems in the upper-Midwest is the Gulf of Mexico with the main source of lift associated with our cyclone are the frontal surfaces. The different styles of lift often lead to very different precipitation characteristics.