Was Phoenix's big storm a monsoon or a haboob? An ASU professor explains the difference

After a very slow start to this year’s monsoon season, metro Phoenix has finally seen some storms this week — including a big one earlier this week.

It was one of those classic Arizona moments when a big wall of dust descended on the city, followed by sheets of rain that drenched the desert. Photographers, TV meteorologists and storm chasers went crazy. The images and time lapse videos went viral.

But, was it a haboob? Or a monsoon? A dust storm? And what does it all mean for this very dry summer?

Arizona State University geographical sciences professor Randy Cerveny joined The Show to explain it all. He’s also the World Meteorological Organization’s Rapporteur of Weather and Climate Extremes.

Full conversation

LAUREN GILGER: Thanks for coming in, Randy.

RANDY CERVENY: Hey, my pleasure.

GILGER: OK, so let's start with this definition. ... The haboob versus monsoons thing. Was this a haboob?

CERVENY: Yes, this was a haboob. This was a dust storm, and it was part of the monsoon. The monsoon is a season. So what we have is a situation where the winds shift. In the wintertime our winds come from the west. During the summertime they come from the south and they bring up moisture from the Gulf of California and from the Pacific Ocean. That's the monsoon.

When we have at the start of a monsoon, thunderstorms that are particularly down towards Tucson, when they die out, they kind of, put out a last gasp of air. And that slams down into the ground like a bomb blast and then spreads out. So, the haboob that we had that came through on Monday actually started all the way down towards Tucson. ... And it was pushing dust up, kind of like a giant push broom. It was pushing dust up all the way from Tucson to here. And it's been dry, so there was a lot of dust to push up. ... But, meteorologists, we prefer haboob. I mean it is a dust storm, but we prefer haboob because kind of like any other science, meteorology uses terms from where they come from.

So, like when we're talking about glaciers. A lot of the terms come from Germany because a lot of the initial work was done in Germany on glaciers. When we're talking about desert-type stuff, the original work was done in the Middle East. So we use Middle East terms like monsoon, which means season, and haboob, which simply means wind.

Amber Victoria Singer/KJZZ

GILGER: It means wind. I didn't know that. OK. People don't like that term, but there it is. [LAUGHS] And you're coming up with a rating system for dust storms like this, is that right?

CERVENY: Actually, we are. We're doing it experimentally, but we've got like 25 different meteorologists around the Valley. From places like the National Weather Service, from SRP, from even local media meteorologists we have involved with this, and from ASU, of course, as well. And what we've done is we come up with a ranking system from, like hurricanes and tornadoes, from 1 to 5. Now it's done as an after-event type thing, like they do with tornadoes. So, we go in the day after we look at all the data that we've collected, and then we can make a determination —

GILGER: So like a Category 1, Category 2, etc.

CERVENY: Exactly. And the Category 5 being the worst, we've only had three in the ... last 15 years. We've only had three Category 5 dust storms. The dust storm surprisingly on Monday only ranked out as a Category 2. And —

GILGER: OK. Not that crazy then. We've seen crazier in recent years, I'm sure. [LAUGHS] What are some of the biggest?

CERVENY: The biggest was the infamous, July 5, 2011, dust storm, the one that made international news that popularized the term haboob actually. But the most recent Category 5 that we had was a couple of years ago. And it was on Aug. 30 of 2023. It happened to be during an ASU football game.

GILGER: Oh, I remember this. [LAUGHS]

CERVENY: That's right. And actually the game had to be shut down for a couple hours as this massive dust ball came into the Valley.

GILGER: OK, so tell us more about the conditions that lead to this in a broader sense. Like I always remember hearing from, probably you in an interview back in the day, that it takes those very, very hot days to get us a big storm like this, right? So I feel like I'm almost — that's the silver lining when it's 115.

CERVENY: Yeah, you can think about it that way, that you have to kind of suffer through the worst in order to get these kinds of storms. Because the way our atmosphere works is hot air rises. That's kind of the critical thing. So during the summertime when we get really hot air on the deserts, then that rises and it starts to suck up air all the way down from Mexico and the Gulf of California. And that moisture comes surging into Arizona. Initially, it takes a while for enough moisture to come in to make wet thunderstorms. So usually the first big thunderstorms that we have during the summer are dust storms. ... And lots of lightning as well, unfortunately. But then as the season progresses, as we get into the end of August and throughout September, they're going to become progressively wetter and wetter. And we'll see less dust storms.

GILGER: OK, so this has been, even though this week aside ... it's been a pretty dry monsoon season, right?

CERVENY: Yeah, part of the problem is that now we have a start date for the monsoon, June 15. And actually here in Phoenix, our thunderstorms don't get going until July 7. So we tend to think, "Oh well, they said it started on the 15th of June." But yeah, it has been dry. We usually would have at least three or four storms between the 1st of July and now.

GILGER: OK, OK. So more maybe on the way, let's hope. But as, you know, our expert on extreme weather here, let me ask you about this summer. It seems less extreme than some very recent summers I remember just dreading.

CERVENY: Yeah, well, we're still hot though. I mean, we are still in the top 10 of hot summers so far over the last 150 years with this particular summer. But compared to the last few, it hasn't been quite as bad. So, that is kind of also a silver lining to what we've had for this summer.

GILGER: It's all relative. Any more moisture on the way, Randy?

CERVENY: Yeah, I think actually the pattern is setting up now that it's going to start to pull in good monsoonal moisture over the next few weeks. So, not immediately. The next few days we're going to be dry, but by the time we get into next week, it'll be active again.

GILGER: OK, so this relatively not-as-hot summer, are we looking at then like to pay off in the fall? Is it going to be a 100-degree Thanksgiving? [LAUGHS]

CERVENY: No, the summertime monsoon is not linked very much to wintertime conditions. So we have to look at things like El Niño. And I can come back and talk about that later on. [LAUGHS]

GILGER: OK. Final question for you — and I'm sure you will come back and talk about that. Tell us a little bit about the commonality of these storms these days. I know we've talked about this before, but it seems as if these big, big haboobs are less common than they used to be.

CERVENY: Well, it's hard to say, frankly. Everybody has cameras now. And so like with this storm that we had on Monday, everybody is taking pictures. If you look at social media, I mean, every picture seems to be of the dust storm. So, I get phone calls from Japan and from Australia saying, "Are you guys still alive there?" Because it looks like we've just been destroyed. But, we don't have any big changes in the intensity or in the frequency of these storms.