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Monsoons Predicted Across Arizona As July Comes To An End

Published: Wednesday, July 22, 2020 - 1:25pm
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MARK BRODIE: All right, so, Steve, it has been very sunny for a very long time. But earlier this week I looked outside and happened to notice something I have not seen for quite a long time.

STEVE GOLDSTEIN: Well, I'm going to break the surprises. I actually, in driving to the office every day, I got rained on twice this week.

BRODIE: Are you kidding me?

GOLDSTEIN: Yes. At first I thought it was bird poop but it was actually rain, yes.

BRODIE: That is that is much better indeed. So monsoon season officially started on June 15. We have yet, though, to see a storm here in the Valley despite the raindrops falling on Steve's car roof. But that could change. That change could be coming soon. And here to give us an update on the forecast and the monsoon season itself is Matt Pace. He is a meteorologist with the Arizona Department of Environmental Quality (ADEQ). Matt, good morning.

MATT PACE: Good morning. Thanks for having me. And I have to ask real quick, Steve. Was that rain or was it sprinkles? That's the big difference.

GOLDSTEIN: Well, all right. See, Matt, you're going have to define this for us, because I was on the 202. This was probably 6:20, 6:30 in the morning on Monday. And it was, it was steady. It was certainly not torrential. It was certainly not a downpour, but it was steady.

PACE: And that's typically what we saw on Monday and Tuesday morning. In fact, Luke Air Force Base actually did measure one-hundredth of an inch of rain. So for Phoenix standards, I think it was probably rain that you experienced, but probably everywhere else, it'd be sprinkles.

BRODIE: So, Matt, I will acknowledge that I am sitting in a windowless closet at the moment. But earlier when I looked outside, it was very, very sunny out. We keep hearing, though, that there could be some storm activity this week. Is still a possibility?

PACE: That is certainly a possibility. If you step outside, you'll notice the humidity is starting to increase. And that's what we're gonna see over the next couple days. And we could start seeing those thunderstorms as early as tonight with some isolated activity. But then Thursday and Friday really look like those bigger storm days where we'll see the storms come off the Rim. But there's a lot of things that go into it, because we don't want that cloud cover like we're seeing the past couple of days, because that doesn't allow the heat on the ground to add fuel to those storms to let them grow bigger. So certainly we like to see these sunny days, especially when you have this moisture to get those storms forming.

GOLDSTEIN: Matt, this is where a little knowledge is a dangerous thing, because I've lived most of my life here, and I always thought that we needed to get up to those really sizzling temperatures in order to create that flow, to build the monsoon. It almost feels weird, like sunny and 114, and then by 5:30, it's raining. How does that work?

PACE: Exactly. And that's one of the things that we see. So the monsoon is that switch in the wind direction. And to get that switch, you have to move that big area, high pressure up over near the Four Corners, over near New Mexico. And that creates that change in wind direction to the east, southeast. Now, since you're talking about high pressure, you're also talking about a lot of heat. So typically, we do get very hot during monsoon. But then if you have the heat of the day and that moisture that moves in, you have a lot of lift in the atmosphere. Think of all that energy going up, interacts with that moisture to form those thunderstorms in the mountains. And now those are able to drop down off the mountains, into the Valley due to all of that heat that you continue to have.

BRODIE: Matt, is it possible to predict at this point whether storms that we might be seeing in the near future will actually include rain, as opposed to just wind and thunder and lightning?

PACE: And these storms will likely produce quite a bit of rain, the ones that do form, because we are getting all that moisture in. So actually, flash flooding does become a concern with any of these storms that form. Now, if we went back to what happened on Monday or Tuesday with that cloud cover, it was still fairly dry down at the surface. So all that rain was basically evaporating before it hit the ground. And then the rain or the sprinkles, whatever you like to call it, hit Steve's windshield. But now, since we've got moisture throughout the entire atmosphere, that rain's not going to evaporate and there are going to be big rain-producing storms. So there's a good chance that Phoenix will see its first measurable rainfall of the season coming in later today, into tomorrow and then Friday.

GOLDSTEIN: Matt, I was tempted to use my wipers, but they were too dried out. So wouldn't it have made a difference and that would have been terrible.

PACE: Right?

GOLDSTEIN: Matt, finally. So because you're with ADEQ, can you give us an idea how the monsoon affects air quality generally?

PACE: Yeah, that's a good question. Typically, what we see, and this is one of the concerns that we will be looking at later today, even tomorrow, is we look at these big dust storms that move in. Obviously we haven't had rain in Phoenix for 102 days. The desert's very dry. So when these storms initially come in, we are going to see those winds move in with those outflows, and that could create quite a bit of dust here in the Valley and stretching all the way over to Yuma. And then as we go throughout the season, obviously the ground gets a lot wetter, the dust threat reduces, and then we start talking about the ozone issues when we have kind of those breaks in the monsoon where we have really hot conditions and we have really light winds. So certainly an up and down roller coaster when it comes to air quality during monsoon.

GOLDSTEIN: Matt Pace, meteorologist for the Arizona Department of Environmental Quality. Matt, thanks as always. And I was gonna say stay dry, but get wet.

PACE: Right? Thank you.


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