When summertime heat ramps up for the Southwest, chances of afternoon thunderstorm activity increase for the region. These conditions usually occur when an upper-level ridge of high pressure builds over the Western States, allowing for sunny skies and increasing temperatures. This strong daytime heat creates low pressure at the surface, which allows for winds to move in from the Gulf of California and Pacific Ocean. Flow over these bodies of water bring abundant moisture with it, what we call monsoonal moisture!
Image credit: Climate Prediction Center/ NOAA
The combination of warm temperatures and monsoonal moisture create some strong and intense, but often short-lived, afternoon thunderstorm activity for the Southwest – from Southern California to the Four Corners region of Arizona, New Mexico, Utah, and Colorado.
These intense storms create very localized rainfall and often associated with flash flooding, because the desert ground cannot handle large amounts of rainfall. The rainfall does not easily absorb into the ground but stays on the surface and creates localized areas of flooding. Flash flooding events can become very dangerous very quickly, so please learn about flood safety before a flooding event affects you and your loved ones! Stay safe out there this monsoon season.
Sometimes the rainfall from these thunderstorms in the Southwest evaporates in the dry desert air before reaching the surface. This is called virga and can create some beautiful scenery. However, this can be potentially dangerous as dry lightning events increase the risk for wildfires.
Dust storms (also known hilariously as haboobs) are also associated with the Southwest Monsoon. These massive dust storms can develop from the thunderstorm’s outflow boundary, created when the downburst hits the ground and picks up dirt and dust from the desert. This creates the appearance of a wall of dust ahead of the storm’s motion. Learn how to stay safe during dust storms before you are caught in one.