Monsoon

June 19, 2013

Transcript:

Ted Simons: The Arizona monsoon season officially started on June 15th, and though we haven't seen dust storms, microbursts or many buildups over mountains as yet, we should be seeing them soon. Randy Cerveny is here to discussion the vagaries of the monsoon season. Every year you come in and I ask the same dumb questions. We will try to vary it a little this year. Why do we start on June 15th, before the storms even start?

Randy Cerveny: Old-timers remember we worried about the dew point, you had to have three days of the dew point being 55 degrees. It tells us whether we have the energy to create a thunderstorm. 55 was a critical number to get a good thunderstorm going. It's a little like the hurricane season. It starts June 1st. Even though we're not going to have a hurricane usually June 1st, we want to get people prepared. If we start the monsoon season preparations on June 15th, we can get the word out to everybody so they know what to do when these thunderstorms roll into town.

Ted Simons: When do the storms usually start?

Randy Cerveny: For Phoenix it's usually around July 7th when we get the first thunderstorms. The problem is -- and the first thunderstorms are not going to be moisture producers. They are going to be dust storms with a lot of lightning and wind with them, very little rain.

Ted Simons: Does it always have to be that way? Why can't we start with a big old gully washer?

Randy Cerveny: It could, but it's very unlikely. These thunderstorms, when they produce rain, even in the higher parts in the early part of the season, they will be producing rain. It just evaporates before it gets down to the ground. The ground and the air near the ground is so dry it sucks up that moisture before it can get down to the ground.

Ted Simons: Where do these storms come from, monsoon storms?

Randy Cerveny: Monsoon thunderstorms are the result of moisture surges that come from the Pacific Ocean and the Gulf of California. That moisture surges up through Arizona and then as it's been lifted, because the elevation here in Phoenix and Tucson and in places in Arizona is higher than the Gulf of California, it gets lifted up and we produce thunderstorms.

Ted Simons: That is why areas like Yuma don't get much monsoon and areas to the east usually do?

Randy Cerveny: Yuma is where we look to see the start of the monsoon, because we can see the moisture surging up the Colorado River, but they don't get a lot of thunderstorms.

Ted Simons: You usually need a few 110-plus days, it has to be crazy hot before the monsoons.

Randy Cerveny: We are coming up on our anniversary of the 122-degree temperature. The heat of the desert acts like a vacuum cleaner. Hot air rises and literally sucks up the air from California and draws it into Arizona. If we didn't have that heat, there would be nothing to really push that moisture up into Arizona.

Ted Simons: That is one of the reasons why it is when we have a really big monsoon storm, the next day it's unlikely to get a repeat?

Randy Cerveny: It stabilizes out the atmosphere.

Ted Simons: Dust storms, where do these -- can you stand there and say a dust storm started right there? They have to start somewhere.

Randy Cerveny: Well, they do. They start from thunderstorms. Usually it's thunderstorms that are quite distant from the Valley that are infamous -- July 5th, 2011, dust storm everybody remembers started down in Tucson. There were very severe thunderstorms that hit the city of Tucson. After those died out they put out a gust of air, that worked its way northward across Casa Grande and northward. As it did, they were picking up dust.

Ted Simons: Somewhere north of Tucson you could say, it started here.

Randy Cerveny: Exactly, exactly.

Ted Simons: As far as monsoon rain is concerned, what areas of the state get the most, what areas of the state get the least?

Randy Cerveny: The areas that get the most are generally the upland areas. The key is you get that moisture pushed up into the atmosphere. So the Mogollon rim gets a lot. Places like Cave Creek. The airport is one of the driest areas. In the entire metropolitan area Sky Harbor Airport is at the lowest elevation. There's no uplift and you don't get as strong thunderstorms.

Ted Simons: That's why Tucson gets the storms, because it's higher elevation?

Randy Cerveny: And it's butting up right against those mountains, so the air doesn't have to travel far to be uplifted dramatically.

Ted Simons: Tucson has more lightning strikes than any other place in the country,that is true?

Randy Cerveny: Florida gets more as a yearly total. During the monsoon, we actually do. Some of the world famous lightning photographers live in Tucson because the lightning is so vivid and impressive, it's some of the best in the world.

Ted Simons: Do some areas get more lightning strikes than others?

Randy Cerveny: Actually there are places. Some have to do with the result of the military. We found out for example that in Yuma sometimes there's less lightning strikes because of the amount of chaffing that goes on when they are testing fighter pilot planes to avoid. They throw out chaff, and it causes more lightning.

Ted Simons: High trees and high elevations?

Randy Cerveny: Yes.

Ted Simons: We understand downdraft, boom, lightning, pull downs everything. Why don't we see more tornadoes with our monsoon storms?

Randy Cerveny: The key to get a tornado is that you have to have, in essence, rotation. In the Midwest and the great plains areas, the rotation is from the result of having a jet stream, a river of very fast-moving air up at 30,000 feet above the storms so that it can literally suck up the air and start its spin. The jet stream at this time of year is all the way up in Canada for us. We don't get that rotation. We'll have the uplift but we don't have anything to really start the spin.

Ted Simons: Last question: I'm not going to ask from you a prediction on the monsoon. Every climatologist says you can't predict. Why can't you predict? Why don't you have an indication of what's going to go on in the next few months?

Randy Cerveny: Because the conditions for conductive thunderstorms are very localized, they depend very much on what the temperature of one small area is compared to another area. Places like the West Valley versus the East Valley. Some years more storms in the West Valley, sometimes in the east. Very difficult.

Ted Simons: Very tricky stuff. Thank you for joining us, Randy, happy monsoon.

Randy Cerveny: And the same.
Ted Simons: That is it for now. I'm Ted Simons, thank you so much for joining us, you have a great evening.