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After weeks of relentless heat, the Desert Southwest is flipping the switch. The North American monsoon, the seasonal wind shift that pulls deep moisture north from the Pacific and the Gulf of California, is arriving, and it will fuel the first widespread summer thunderstorms across the interior West this weekend into next week.
As AccuWeather explains, southerly winds are drawing increasing moisture into the region as an area of high pressure settles over the Four Corners, the classic setup for daily rounds of afternoon and evening storms.
Those storms are a double-edged sword. They can deliver much-needed rain to drought-parched land, but they also bring gusty outflow winds, walls of blowing dust, torrential downpours, and dry lightning capable of sparking new wildfires. According to WeatherNation, the strong, dusty outflow winds can sharply reduce visibility along area highways, while frequent lightning threatens hikers and anyone caught outdoors.
Peak Danger
Sunday into Monday, when better moisture spreads across southern Arizona and localized flash flooding becomes possible, and when the dust storm threat is elevated during the first significant monsoon "burst" of the season.
What to Expect
- Scattered to numerous afternoon and evening thunderstorms across Arizona, New Mexico, southern Utah, southern Colorado, and Nevada.
- Gusty outflow winds and blowing dust, including the potential for haboobs, or large dust walls, that can reduce highway visibility to near zero in moments.
- Heavy downpours capable of dropping an inch or more in a short time, triggering flash flooding in dry washes, canyons, and burn-scar areas.
- Frequent lightning, including dry lightning that can ignite new wildfires in areas that get little rain from a passing storm.
Road Conditions
Two hazards dominate the driving picture. First is dust: outflow winds racing ahead of a collapsing storm can kick up a dust wall that drops visibility from miles to feet almost instantly, a leading cause of chain-reaction crashes on Interstate 10 between Phoenix and Tucson. Second is water: the desert's sun-baked, hardpan soil cannot absorb heavy rain, so washes and low crossings that are bone dry in the morning can become fast-moving torrents by evening. Roads through canyons and normally dry riverbeds are especially dangerous, and mountain routes near recent burn scars can flood with little warning.
Where and When, Plus the Fire Concern
The NWS notes that monsoon rain does not fall every day but comes in a series of "bursts" and "breaks." Some of the most active storms over the coming days are most likely in Phoenix, Flagstaff, and Tucson, Arizona; Albuquerque, Santa Fe, and Las Cruces, New Mexico; Las Vegas and Elko, Nevada; El Paso, Texas; and Grand Junction and Durango, Colorado. In Maricopa County, forecasters flagged an elevated dust storm threat this weekend and growing flash flood potential Sunday into Monday. Early in the monsoon, dry lightning is a real wildfire concern, since the season's first storms can spark fires before the landscape has had a chance to green up.
Dust and Flash Flood Driving Tips
- If a dust storm approaches, Pull Aside, Stay Alive: pull completely off the roadway, put the vehicle in park, turn off all lights including hazards so other drivers do not follow you off the road, take your foot off the brake, and wait it out.
- Never drive into a flooded wash or low crossing. Water depth and current are almost impossible to judge, and in Arizona the "Stupid Motorist Law" can leave you liable for the cost of your own rescue.
- Slow down and increase following distance when storms are nearby, since sudden downpours and gusts can hit fast.
- Avoid parking in dry riverbeds or low-lying areas, and do not start a hike or drive through a canyon if storms are in the forecast upstream.
- Keep headlights on in blowing dust only while moving, and watch for stopped vehicles ahead.
Timing
Storm coverage increases this weekend and likely persists through much of next week as the monsoon strengthens. The Weather Prediction Center expects monsoonal moisture to keep producing showers and storms across the Southwest, the Four Corners states, and northward into the northern Rockies and High Plains, with the best chances for wetting rain and localized flash flooding across southern Arizona from Sunday onward.
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