Precipitation Patterns

Mid-latitude cyclones

A "cyclone" is a low-pressure system and "mid-latitude" is between the Equator and the Arctic Circle. These are the regular weather systems that often bring cold fronts in winter and spring.

Atmospheric rivers

These are narrow "rivers" of water in the sky and can sometimes move along a mid-latitude cyclone. The western U.S. can receive 20-50 atmospheric rivers every year.

Monsoon and tropical cyclones

Both the monsoon season and remnants of Pacific hurricanes can bring moisture into the southwest U.S. which helps build thunderstorms in the summer.