- The monsoon in the Southwest runs from June 15 through Sept. 30.
- Last Ky monsoon was the 20th-wettest on record.
- Heavy rain, flash flooding, lightning, downburst winds and dust storms are threats.
The Southwest monsoon season officially kicks off June 15, but it’s usually slow to start this region.
Monsoon season starts Wednesday in the southwestern US and lasts through Sept. 30, according to NOAA. However, in most of the region, it doesn’t really kick in until late June or early July.
The monsoon is a seasonal change in the southwest, which helps draw moisture into the Southwest. This can fuel the development of showers and thunderstorms in the region, with the coverage of those storms varying day-to-day or week-to-week.
Most of northwestern Mexico and the southwestern US receive over half of their annual precipitation from the monsoon.
But not every year is equal, and the monsoon can produce different results each summer, as we’ve seen the past two years.
The analysis from the National Weather Service in Phoenix covered last year by the 20th-wettest dating to 1895 for the area stretching from Arizona to New Mexico and southwest Texas. This is the driest monsoon on record for the same area.
This is the largest rainfall in the Southwest, according to the National Weather Service. That’s because there is no clear signal for how the monsoon pattern might set up this summer.
The exception is south-central and southeast Arizona, where odds are tilted toward a wetter than average monsoon.
The first monsoonal thunderstorms of summer 2022 could impact the Southwest as soon as this weekend (June 18-19) from a surge of moisture headed into the region.
How the Monsoon Develops
Hot and dry conditions, with low humidity, prevail in June before the monsoon really gets going.
Fire danger is high due to these conditions and heat can be oppressive, especially in the deserts of Arizona, southeastern California and southern Nevada.
The seasonal wind shift occurs gradually throughout the summer when the thermal bodies develop, but large bodies of water nearby do not warm as quickly. In addition, a ridge of high pressure builds over the Rockies or Plains.
Eventually, pressure differences between the warm land and cooler water cause more humid air from the gulfs of California and Mexico to be drawn toward the Southwest. This flow from the ocean to the ocean.
The result is thunderstorm development.
Rain from these storms causes humidity to increase, which triggers more storms. This cycle continues until early fall, when the land finally cools and water temperatures reach peak warmth, which reduces the pressure difference.
Beneficial, but Also Hazardous
Rainfall from thunderstorms reduces the risk of wildfires and brings much-needed rain to the region for reservoir replenishment and vegetation.
The monsoon pattern also brings concerns, including flash flooding, lightning, downburst winds and dust storms.
Flash flooding is the leading thunderstorm-related killer and most flash flood deaths occur in vehicles. Never drive through flooded roadways. Lightning also causes injuries and fatalities every year in the United States.
Downbursts are another concern – they can result in an outward burst of damaging winds on the ground. Outflow boundaries created by strong thunderstorm winds can cause blowing dust and potentially dust storms, which can significantly and quickly limit visibility.
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