What a haboob is, and what to do when one arrives

The dust arrives as a wall, and that is the whole of the description. A haboob is not a hazy afternoon that thickens; it is a defined edge on the horizon that reaches you at speed, with clear air on one side of it and almost nothing on the other. Drivers meet it on the I-10 between Phoenix and Casa Grande and on the Loop 202 out towards the Superstitions, and the reason the Arizona agencies write about it the way they do is that people keep driving into it.

What actually makes the wall

A haboob is an outflow phenomenon, which is to say it is made by a storm rather than by the wind in general.

A thunderstorm builds a column of air that rises until it can rise no further, and then that air comes back down: fast, and loaded with rain that evaporates on the way. The descending air hits the ground and has nowhere to go but sideways, and it spreads out from the storm in every direction as a gust front. In a desert in early summer the ground under it is bare and dry and the storm’s base sits high, so the outflow picks the soil up almost immediately and carries it out ahead of the rain.

Two things follow from that, and both matter to somebody deciding what to do. The dust arrives before the water, so the wall is a warning of a storm rather than the storm itself. And the same outflow that carries the dust is a wind event in its own right: the gusts ahead of a monsoon storm are what take roofs off and put a trampoline through a power line, and they arrive while the sky is still orange rather than black.

Why it belongs to the front of the season

Dust storms are not spread evenly through the monsoon window. They cluster where the calendar says the season has started and the moisture says it has not.

The line tells the story. The window opens on 15 June with a normal dew point of 36 °F, which is desert-dry air. It does not reach 55 °F until 16 July. Those first four weeks are the build-up: the ground is at its driest, the storm bases sit at their highest, and the rain mostly evaporates before it lands. That is precisely the recipe for an outflow that carries soil instead of water.

Once the moisture arrives in the second half of July, the storms come lower and wetter, and they bring rain with the wind. Dust still happens (a strong outflow will lift whatever is loose) but the peak of the dust season is the front of the monsoon, not the middle.

That is worth knowing for a practical reason. A dust storm in the last week of June is not a sign that the wet season has failed to arrive; it is what the wet season looks like before it starts. The Monsoon Season Clock reports the dew point against the same 55 °F line, which is the honest way to tell whether the season is early or late in a given year.

The instruction that surprises everybody

Every agency says the same thing, and it is the one people argue with: turn your lights off.

Not the headlights while you are parked, not the hazards instead of the brakes: all of them. Maricopa County’s instruction names the emergency flashers explicitly, and the National Weather Service’s Phoenix office says the same thing from the other direction, with a line about making sure all of your lights are off when you park off the roadway.

The reason is stated by both, and it is a fact about the driver behind you rather than about you. In near-zero visibility a person steers at whatever they can see, and if the only thing they can see is the red glow of your tail lights half a car ahead, that is where they will aim. Being visible is the thing that gets you hit. The county’s own framing of the timing is in the same spirit (do not wait until there is low visibility to take action) because the decision is only available while you can still see well enough to make it.

The Dust-Storm Decision Flow draws the whole sequence situation by situation, which is easier to follow than a list when the wall is already at the end of the road.

If you are driving

This is where dust storms kill people, and almost never by choking them. ADOT’s campaign line is in capitals because it is the entire first step: never drive into a dust storm. The campaign’s own description of the timing is that visibility can go to near zero in a matter of seconds, which means the thin part you can see is the last part you will see.

The sequence after that is short.

Do not rejoin the road until you can see the road. The same outflow that brought the dust is still moving, and the vehicles that pulled over near you are still there.

If you are at home

A dust storm at home is a high-wind problem with a cleaning problem attached.

The preparation that matters is the ten minutes before it arrives, and it is about things that fly. The utility that owns the lines names umbrellas, kiddie pools and trampolines specifically, and gives the reason: they get swept up by the wind and end up in power lines, turning a storm on one street into an outage on another. Patio furniture, bins and anything else loose belong inside a garage rather than against a wall.

Once the wind is up, the city’s severe-weather guidance is the same as for high wind: get inside, shut it up, and take a central interior room with no windows. The dust is the secondary concern; the debris the wind is carrying is the primary one. Windows closed means windows closed, because the alternative is a layer of grit on every surface in the house.

Afterwards, it is worth checking the roof drains and scuppers. They silt up in a dusty season, and the storm that needs them clear is the next one. The Monsoon Prep Checklist Builder puts that job on a calendar with the rest of the season’s work.

If you are on foot

This is the worst of the three places to be, and the guidance is thinnest here because the good options run out quickly.

The first choice is a building: not a vehicle, not a shade structure, a building. If there is no building within reach, the city’s advice for being caught outside in high wind is to lie flat in a ditch or a low-lying area with your hands protecting your head. That advice is about the wind and the debris in it. The dust is unpleasant and abrasive; what hurts people outdoors in a dust storm is what the wind is carrying.

While you wait, stay away from anything that can come down: trees, poles, signs, and the loose material the storm has picked up. And do not keep walking. The instinct is to carry on to wherever you were going, and in near-zero visibility, on foot, beside a road where nobody can see you either, that is the decision that turns ten bad minutes into an accident.

One more number belongs here, because it applies after almost any monsoon storm: if a power line comes down, both Arizona utilities give a distance of 100 feet, and both add that electricity can travel through the ground. City of Mesa publishes 20 feet. Where a city and the utility that owns the equipment disagree, this site uses the utility’s figure.

What this page does not cover

The health effects of breathing dust. That belongs to a public health agency, and the pages this site needed to source it would not open when the article was written, so the honest thing is to say so rather than to source it second-hand from a news story.

What is covered here is what the Arizona agencies publish about the storm itself: how it forms, when in the season to expect it, and what to do in the three places you might be standing when it arrives. The decision flow is the fastest route through the three of them. The microburst article covers the wind that arrives with the same outflow but without the dust, and lightning safety is the other hazard in the same storm.