Phoenix was engulfed by its second Category 5 dust storm of the week early Thursday, only three days after another extreme haboob swept across the Arizona capital.
Both storms reached the highest level on the new PHX Dust Storm Scale developed by Arizona State University researchers. Thursday’s event became only the sixth Category 5 dust storm identified in Phoenix-area records dating to 2010.
The back-to-back Category 5 classification is unprecedented during the period studied by researchers.
Category 5 in this case describes extreme airborne dust concentrations and exposure. It is unrelated to the scale used for hurricanes.
A huge dust storm is affecting in Phoenix, Arizona, US 🇺🇸 (25.08.2025) pic.twitter.com/f749xASvSr
— Disaster News (@Top_Disaster) August 26, 2025
What caused Thursday’s Phoenix dust storm?
The haboob was driven by outflow winds from weakening thunderstorms near Tucson.
When a thunderstorm begins to collapse, rain-cooled air can descend rapidly and spread outward after reaching the ground. This creates an outflow boundary that behaves like a miniature cold front.
As the boundary travelled north toward the Phoenix metropolitan area, its strong winds lifted loose soil and sand from the dry desert surface. The result was a fast-moving wall of dust capable of sharply reducing visibility and sending particulate matter concentrations to dangerous levels.
Wind gusts of at least 40 km/h (25 mph) were recorded at several monitoring locations, while broader assessments indicated that some winds associated with the event approached 80 km/h (50 mph).
The storm reached the Valley during the early hours of Thursday, helping to limit the number of vehicles exposed to the worst visibility conditions.
Dust concentrations reach 5,841 µg/m³
The highest dust concentration was measured at an air-quality monitor in western Chandler shortly after 1 a.m.
Particulate matter peaked at 5,841 micrograms per cubic metre, or µg/m³, an exceptionally high concentration that placed the event in Category 5 on the PHX Dust Storm Scale.
Elevated concentrations persisted for approximately three hours and were detected by numerous monitoring stations across the Valley.
Visibility fell to around 0.8 kilometres (half a mile) during both of this week’s dust storms, creating potentially dangerous conditions for motorists.
The newest storm affected Chandler most severely, with the dust spreading northward into Tempe, Scottsdale and northern Phoenix.
How did the two Category 5 storms differ?
Although both storms received the same extreme classification, researchers found significant differences in their geographical footprints.
Thursday’s haboob produced its highest concentrations around Chandler and then extended north through parts of the metropolitan area.
The earlier storm on Monday night covered a broader section of the Valley. High dust indicators were detected across a larger area, and unhealthy air remained over Phoenix into Tuesday.
The events were classified as the fifth and sixth Category 5 dust storms recorded since 2010. Arizona State University climatologist Randall Cerveny described the occurrence of two such storms only days apart as unprecedented in the available record.
Why Phoenix’s dry ground made the storms worse
A lack of recent rain in central Arizona played an important role in the severity of both storms.
Rain normally removes some dust from the atmosphere and dampens the ground, making soil particles heavier and more difficult for the wind to lift. Rainfall can also support vegetation that helps hold the soil in place.
When the surface remains dry and sparsely covered, thunderstorm outflows can collect large quantities of loose dust as they travel across the desert.
ARIZONA #HABOOB: On Monday evening, a massive dust storm engulfed the Phoenix metro area as severe thunderstorms swept through the Valley. The blinding wall of dust led to numerous flight disruptions at Phoenix Sky Harbor International Airport. #AZwx pic.twitter.com/Dat9SA3ShB
— WeatherNation (@WeatherNation) July 14, 2026
Phoenix typically experiences between five and 15 dust storms each year. Eight events have been recorded so far this season, placing the overall number within the expected range.
What makes this season unusual is not the total number of storms, but the intensity of the two most recent events.
What does a Category 5 dust storm mean?
The ASU-led PHX Dust Storm Scale ranks events from Category 1 to Category 5 using measurements including particulate concentrations, wind speeds, duration and geographical coverage.
Researchers developed the system to assess exposure to dust and fine particulate matter using monitoring stations across Maricopa County.
According to ASU researcher Ryan Heintzman, a person outside for one hour during a Category 1 storm could inhale approximately 250,000 dust particles. During a Category 5 event, exposure could exceed one million particles.
The smallest particles can penetrate deep into the lungs. People with asthma, heart or lung disease, older adults, young children and immunocompromised individuals face greater health risks.
What should drivers do during a haboob?
Dust walls can arrive quickly and reduce visibility to near zero. Drivers should avoid entering a dust storm whenever possible.
The National Weather Service advises motorists caught in blowing dust to leave the roadway, stop as far from traffic as possible, apply the parking brake and turn off all vehicle lights. Keeping lights illuminated can cause other drivers to follow them off the road.
Residents should remain indoors, close windows and limit outdoor activity until dust concentrations decline, particularly after an extreme Category 5 event.
