Arizona Horizon Banner

June 15, 2009

Host: Ted Simons

The Start of the Monsoon

  • June 15th marks the official start of Arizona’s monsoon season. ASU’s Randy Cerveny talks about the monsoon and his new book “Weather’s Greatest Mysteries Solved!”
  • Randy Cerveny - ASU professor

View Transcript
Ted Simons: Despite our sunny skies, today is the official start of Arizona's monsoon season. At least as far as the National Weather Service is concerned. Joining me to talk about the monsoon is Randy Cerveny. He's an A.S.U. professor of climatology and the author of a new book entitled, "Weather's Greatest Mysteries Solved!" Thanks for being on the show. Good to see you again.

Randy Cerveny: My pleasure.

Ted Simons: The monsoon starts today, June 15th. We've decided on a date. Why June 15th?

Randy Cerveny: We’re patterning it over what they do in Florida with the hurricane season. Even though we don't have hurricanes the first of June, usually, they classify the start as June 1st. The idea is we want to get people aware of what the monsoon is, what to do about it. Preparations to make and we can do that without having those annoying thunderstorms taking up the news media at that time and get the message out about safety.

Ted Simons: Has the monsoon ever started this early?

Randy Cerveny: You know, normally starts around the first of July, or the seventh of July, if we look at the traditional way of doing it. But in order to get the monsoon, you have to have a lot of hot air that takes the month of June to build up over Arizona and then that fields -- fuels up the moisture to come into the state.

Ted Simons: So its true, the 115-degree temperature, while a lot of people bemoan it. The idea is that draws up that moisture from Mexico.

Randy Cerveny: It acts like a big vacuum cleaner and sucks up moisture from the Pacific Ocean.

Ted Simons: Global climate change, whatever the reasons for it, something is going on out there. Is it affecting the monsoon?

Randy Cerveny: It's one of the things we look at. We have record that's go back over 100 years in terms of rainfall and temperatures and these things. There have been changes to the monsoon. We don't know all the changes and what they're caused by, but we found for example the number of dust storms we get into Phoenix has decreased in recent years as a result of the fact, not of any changes in climate, but rather that the city is built up so we don't have as much dust in the atmosphere.

Ted Simons: It seems like 30 years ago, we were always getting dust storms and cloud formations over the east and south. You're saying the clouds may be there but the dust is not?

Randy Cerveny: If you have strong winds of 40, 50 miles per hour, in order to get the wall of dust we remember seeing at least once or twice during the monsoon, we have to have the dust on the ground. If you put pavement over it, you don't get the dust in the area.

Ted Simons: The asphalt and pavement affect the dust, what about storms in general? Do these monsoons go around the city?

Randy Cerveny: It's not because of the city itself. It's because of the topography. The sky harbor airport is the lowest part of the metro area. Thunderstorms are most active when they’re moving up slope, so places like cave creek get more rain than sky harbor airport.

Ted Simons: Is that why if you live in the east valley, you're getting storms at least a couple times a week, but out in buckeye and the west valley, seeing them from a distance?

Randy Cerveny: To some extent that’s true. We know there are year to year changes where the thunderstorms hit. Sometimes it's the west part of the valley, sometimes the east. Sometimes it’s the west valley. And we don't understand why. But there's a lot of influence by topography.

Ted Simons: I was going to say, predicting monsoons, how do you do it and how accurate can it be?

Randy Cerveny: Well, we keep trying. We haven't gotten that accurate yet. One of the problems, it's a hit-and-miss type of situation, that because it's made up of individual thunderstorms, it's not like the classic cold front that you have in the great plains. Its comprised of just individual little thunder storms. You can have a situation where some parts of the valley get drenched with two inches of rain by one thunderstorm and yet other parts are clear and don't get a drop. Forecasting becomes problematic.

Ted Simons: How about the idea that the conditions will be ripe for a stronger monsoon this summer?

Randy Cerveny: We try it and the climate prediction center is claiming that -- predicting that the northern part of the state will be slightly above normal in terms of their annual or their monsoonal rainfall. We average about six inches of rain.

Ted Simons: These microbursts are energized -- what? -- focused areas of intense thunderstorms?

Randy Cerveny: Right, it's something that's relatively new. You wouldn't think after studying weather for this long, we'd still be discovering new things. But recently, meaning within the last 30 years, we discovered this whole new idea of microbursts, in essence, air bombs that blow out of the bottom of a thunderstorm and smash into the ground and spread out like a bomb blast and they were first discovered with a big plane crash that happened in New York City. But we discovered in the desert they're common because when they hit the pavement and get that dust up in the atmosphere, we can see a little bit of a signature and so a lot of the work that's been done in studying microbursts has been done in the desert.

Ted Simons: A quick question. Rainiest spot in Arizona for the monsoon?

Randy Cerveny: Up in the high mountain areas like Flagstaff. That because of the moisture that comes up from Mexico, gets pushed up the mountains and if you go to Flagstaff, usually about every day or other day, 3:00 or 4:00 in the afternoon, you get a big thunderstorm that breaks. They work their way down to Phoenix, but usually dry out before they get here.

Ted Simons: And the dryest place?

Randy Cerveny: Well, normally that would probably be Yuma. They end up with about three inches of rain for the entire year.

Ted Simons: Great stuff. Thanks for joining us. Congratulations on the new book as well.

Randy Cerveny: Thank you very much.

Ted Simons: Coming up on "Horizon" -- The latest on the budget standoff between the governor and state lawmakers. And a debate on plans to place a moratorium on fees that cities charge homebuilders to help pay for growth. That's Tuesday at 7:00 on "Horizon." Wednesday we'll take a look at A.S.U.'s involvement with NASA's efforts to return man to the moon. Thursday, empty storefronts and high-rise condominiums are signs that the economy has taken a toll on Mill Avenue. Find out what's being done to reinvigorate downtown Tempe. And Friday, it's another edition of the Journalists' Roundtable. That is it for now. I'm Ted Simons. Thank you so much for joining us. You have a great evening.


What's On?


Need help accessing? Contact

Eight is a member-supported service of Arizona State University    Copyright Arizona Board of Regents