It was a sight to behold — one of the most incredible AccuWeather storm chaser Reed Timmer had ever witnessed up to that point in July 2018. A massive mile-high wall of dust was barreling toward afternoon commuters along Arizona interstates 17 and 8 near Phoenix. The ominous burnt-red curtain packed hurricane-force wind gusts, hail and torrential rains, choking rush hour traffic in near-zero visibility as it made its way westward.
If you’re not from the Southwest (or live along a huge desert like the Sahara or Arabian Peninsula), chances are you’ve never heard the word. Haboobs (pronounced hah-boob) are particularly intense types of dust and/or sandstorms that envelop areas for relatively short periods of time, typically 30 minutes or less.
“They’re caused by the small scale, but intense, processes of thunderstorms and the resulting winds,” says Dave Houk, senior meteorologist with AccuWeather. Comparatively, “the more common ‘dust storm’ is generally driven by large scale winds with strong low- and high-pressure systems and is less sudden and not as intense but can be longer in duration.”
These humongous dirt blogs are more likely to occur during the summer monsoon season in the Southwest U.S. as well as across North Africa and the Middle East. Places like Phoenix, Arizona, average several haboobs each year but they are far more common in Sudan in the Sahara Desert, Houk says.
Unlike many other meteorological terms with strict scientific definitions based on measurable characteristics — such as those that discern a tropical storm from a hurricane — with haboobs, there is no strict set of rules that lead to a scientific classification.
However, Houk says, “There are characteristics, though, that lead meteorologists to call it a ‘haboob.'”
What Makes a Haboob a Haboob?
You can usually see the sharp leading edge of a haboob’s wall of dust and sand in the distance. The winds at the ground that accompany and fuel it typically gust to 30 to 60 miles per hour (48 to 96.5 kilometers per hour) or more. These massive clouds can extend vertically into the atmosphere for 10,000 feet (3,048 meters) and span as wide as a mile (1.6 kilometers). “But sometimes organized lines of thunderstorms that stretch more than 50 miles [80 kilometers] can pick up sand and dust along the entire line when conditions are right,” Houk says.
If you’re unlucky enough to get caught in one, he adds, “you can expect the visibility to be greatly reduced, even near zero, at ground level as the sand/dust cloud moves across the area.”
What Causes a Haboob?
Haboobs are typically associated with the smaller scale processes involved with strong upward, downward and outward winds of a thunderstorm or a shower, Houk says. “We like to say ‘what goes up, must come down,’ and that is true when we talk about rising air.” Rising air creates showers and thunderstorms that can move at speeds of up to 100 miles per hour (160 kilometers per hour).
“As the strong upward motion causes a building thunderstorm, the rain that starts to fall from the thunderstorm starts to create areas of downward moving air,” he says. “That downward rush of cooler air coming down around the periphery of the core of upward moving air in the thunderstorm can be enhanced as evaporational cooling and downward falling raindrops add additional speed to the downward moving winds.”
When those downward rushing winds hit the surface of Earth, they have nowhere to go but outward in the horizonal plane, typically strongest ahead of the core of the thunderstorm in the direction the thunderstorm is moving, Houk says. “We call the leading edge of these propagating winds a ‘gust front’ or ‘outflow’ from the thunderstorm.”
A haboob forms when the downward rush of air reaches the ground and lifts the dust and sand up. That dust gets caught in the turbulent winds associated with the circulation of the parent thunderstorm and begins to move along with the gust front.
Are They Dangerous?
Haboobs can damage property and threaten lives, Houk says. The sudden onset and low visibility for ground and air traffic can cause accidents, slowdowns and stoppages. Gusty winds can cause power outages and downed trees. Wind-driven dust can scour vehicles and homes causing paint and surface damage.
Airborne dust and sand also create a respiratory hazard. And lightning and heavy rains that accompany thunderstorms can carry the risk for injury, fires and flooding.
If you’re in the path of an oncoming haboob, the best thing you can do is seek shelter indoors, Houk says. If you’re driving, pull over in the safest place you can find. “If caught outdoors, cover your face with a cloth or clothing to prevent the particles from entering your lungs.”
You can also take comfort in knowing that these dust storms are often short-lived. “The haboob often outruns the advancing and decaying thunderstorm that has caused it,” Houk says, “and the sand/dust storm [often] dissipates in 10 minutes.”