Get to Know Your Monsoon
The North American Monsoon is a rainy season in the desert Southwest from June 15 – September 30. The season is defined by a wind shift bringing tropical moisture up from Mexico, sparking widespread thunderstorms.
Summer rains typically start in late June to early July, when a zone of high atmospheric pressure settles near the intersection of Arizona, Utah, Colorado, and New Mexico. Prevailing westerly winds north of this “Four Corners” high-pressure zone help it spin clockwise, pulling moisture mostly from the Pacific Ocean but also from the Gulf of Mexico north into the western U.S.
The monsoon then progresses from south to north with northern parts of Arizona seeing rainfall within a week or two after rainfall starts in southeastern Arizona. Monsoon storms can bring dangerously heavy rain, localized flash flooding, damaging wind, lightning, and dust storms. Thunderstorm activity typically starts to wane in the first or second week of September as moisture retreats to the south.
Tropical storm activity can pick up at this time, as well, and some storms travel up into Arizona, bringing widespread heavy rainfall. These rain events are technically not part of the monsoon. Some parts of the Southwest get half their annual rainfall during monsoon.
Read more in an in-depth look at monsoon by Arizona Cooperative Extension Specialist Mike Crimmins, Ph.D.
Southern Arizona monsoon rain normally starts in early July, though rain could start any time from late June to late July. Southeast Arizona usually sees rain before other parts of the state.
The dew point can help you track when the monsoon is likely to start in your area. When the dew point hits 55 degrees on three consecutive days, the chance of monsoon rain is high.
What’s on the Horizon? – Published by the Climate Assessment for the Southwest (CLIMAS), this collaboration between University of Arizona and Mexico State University offers a look at what to expect in the
Southwest’s climate.
Regional Monsoon Maps – UArizona maps that are updated daily with rainfall totals, number of rain days, and rainfall total compared to average.
Arizona Monsoon Maps - State maps updated daily showing total precipitation and rain event intensity and frequency.
Real-time Weather Monitors – Get real-time rainfall and temperature data from dozens of monitoring sites across Arizona and New Mexico
In-Depth Climate Podcasts Get up to speed on monsoon, winter rain, global climate systems, and more.
Watch Arizona Get Green – This map shows how green the nation is on any given day. Check back to track Arizona’s "green up” as monsoon rain sparks an annual explosion of plant life.
Be a Citizen Scientist– Check reported rainfall amounts in your neighborhood or sign up to report rainfall data from your back yard. Rainlog data for ranchers and other land managers.
Track Our Drought – Check the Standard Precipitation Index (a measure of drought) for your area in near real-time based on precipitation measurements from multiple sources.
WEBCAM - View current weather conditions on the Hydrology & Atmospheric Sciences cloud cam (live view)
