The Weather Service's Phoenix forecast is hotter than the weather app on your phone. Here's why

LAUREN GILGER: Have you ever noticed that the weather forecast on TV, or from our own Bruce Drummond or Phil Latzman here on the radio, might say, "We’re looking at record heat today — it’s going to be 112 today!" But, if you open up your weather app on your phone, it’ll say something entirely different?

Mine today says 108. But Bruce over there in our master control studio is reporting a high of 112 degrees. That’s a pretty big difference! And don’t even get me started on the alarming numbers that pop up when you get into your car.

So, why does this happen? And, more importantly, who’s right?

For more on that, I’m joined by our favorite extreme weather expert here on The Show, Arizona State University professor of geographical sciences Randy Cerveny. Hi there, Randy, thanks for coming in.

Amber Victoria Singer

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KJZZ

RANDY CERVENY: Hey, my pleasure.

LAUREN GILGER: OK, so clear this up for us. There is kind of a consistent difference, it seems, between this reported forecast that you’re going to hear on the news and the records even that we see, or what you’re going to get when you open up your phone. What’s the difference here?

RANDY CERVENY: Well, the phones are not using the National Weather Service forecast. The phones are using their own AI-based computer model forecast. And there is basically not a lot of information on exactly what goes into their particular models and how good they are.

LAUREN GILGER: So, they have their own models, you don’t even know exactly where they’re coming from.

RANDY CERVENY: Right, exactly. And they don’t really want to give us that information either. ... So, basically, the place where you really want to try to get your good forecast is going to be the National Weather Service.

LAUREN GILGER: OK. And that’s what, of course, we’re reporting. ... But like, so Phil Latzman, for example, on on Morning Edition here at KJZZ, will tell you he hears a lot from folks that, you know, they’re annoyed that he’s reporting a temperature that’s so much higher than what they’re seeing on their phone.

And there’s another layer to this, too, because people will say like, "You know, it’s not 115 here in Cave Creek or in north Scottsdale where I am." You know, does this also have to do with where folks are in the Valley and where those National Weather Service official temperatures are coming from?

RANDY CERVENY: Absolutely. And that’s the thing is that the Valley is so big and has such a complex terrain that we have lots of what we call microclimates. That the actual temperature at one place here in Tempe, for example, versus another place that is Arcadia, are going to have two entirely different temperatures compared to, say, Cave Creek. So, what generally happens is that the hot spot of the entire Phoenix metropolitan area is Sky Harbor Airport.

Christina Van Otterloo

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KJZZ

LAUREN GILGER: Where we take the temperatures.

RANDY CERVENY: Right. And there’s a couple of reasons for that. It is at the lowest elevation for this area and low elevations are going to be the hottest, and it’s also just a lot of concrete, a lot of asphalt and a lot of desert terrain.

LAUREN GILGER: Yeah, it’s an airport. So, I mean, is it accurate that we take our official forecasts at Sky Harbor?

RANDY CERVENY: Well, there are actually probably better places to put it, because our airport is using every little space now that it can use. It used to be that we would have some natural terrain. You always want to put a weather station where there is natural terrain so it’s reflective of the the area, not of a specific site. And unfortunately, at Sky Harbor, yeah, there is less and less natural terrain.

LAUREN GILGER: OK. So, is that a discussion in the weather world, Randy, that maybe we should put this somewhere else?

RANDY CERVENY: Yes, it is, actually.

LAUREN GILGER: I can tell. OK, OK. A good discussion, what do you think, this is a good idea to talk about?

RANDY CERVENY: Well, the the problem is going to be the Federal Aviation Commission. They don’t want to move — they have a reason for having the weather station at Sky Harbor. They need it for their for their planes. ...

For people that are in the Phoenix metropolitan area, yeah, Sky Harbor probably is not the best representative site for giving us the weather.

LAUREN GILGER: OK. So, National Weather Service is going to be your most accurate, but it’s coming from Sky Harbor.

So, let’s talk about one other big question here that we get from folks, which is about that car thermometer, right? Like, those are, I mean, downright scary numbers you get in your car sometimes if it’s been sitting out in the sun. It’s going to say it’s 130.

RANDY CERVENY: Yeah. And I’ve, I’ve actually had people call me up and say, "Well, I’ve set the new highest record for the Phoenix metropolitan area because my car temperature said such and such." Well, no, the problem is that we have very strict standards as to how temperature and other weather variables need to be measured. All weather measurements have to be done in the shade.

Your car sitting there in the sunlight with the thermometer generally associated with somewhere on the dashboard is not going to be representative of the surrounding area.

LAUREN GILGER: So, take that with a grain of salt, OK. That makes me feel better. OK.

Let me take the last couple of minutes here, Randy, to talk to you about monsoon season, which officially kicked off pretty recently here, but we have not seen a lot of rain. It’s been threatening to rain a little bit here and there, but not much has come down. But we are hearing that we are about to get this summer, this "super El Niño" coming out of the Pacific Ocean. What’s this about?

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RANDY CERVENY: Well, we generally have in, around the start of the monsoon on the 15th, a surge of moisture that comes up from the Gulf of California. That starts to lay the foundations for the monsoon. Then we get usually a little drying out. That’s what we had going on this week, and that’s why we’re going to get up to 112 today at Sky Harbor.

But then what’s going to happen starting next week is that we’ll get the return of the moisture, and we’re looking at a fair amount of moisture coming into the state. Likelihood is that thunderstorms won’t only just be located up on the Rim, but they will come down into the Valley as well.

LAUREN GILGER: OK, so this is promising in terms of actually getting some rain this monsoon season, which has not happened every monsoon season of late. But is it going to be too much? Are we looking at flooding? Are we looking at, you know, pretty scary conditions?

RANDY CERVENY: Oh, we’ll always get some flooding because, unfortunately, a lot of our man-made infrastructure promotes that. When you build roads and such, the water doesn’t have a chance to soak into the soil anymore and it runs off.

So, yeah, whenever we have monsoon thunderstorms, we will likely have some flooding. It depends on how extensive are the thunderstorms as to, you know, whether they’re going to cause massive problems or not.

LAUREN GILGER: Yeah, yeah. OK, so could be some flooding, could be a good amount of rain. I mean, I wonder when we’re talking about heat and just how hot the summers can get here, are we looking at some pretty high humidity numbers as well, which we are not used to in the Valley?

RANDY CERVENY: Yeah, we’ll, we’ll definitely be moistening up the atmosphere. You noticed that this morning, actually, the dew point jumped up from the 40s up into the 50s.

Now, the biggest thing, though, ... that we normally want to play very close attention, especially this next week, is going to be wildfires because when these first dust storm — or when these first thunderstorms create, come into the Valley, they’re going to create dust storms. And the dust storms are going to have a lot of wind with them, and they’re going to have lightning. And those are the two ingredients that you really need for wildfires, I’m afraid.

LAUREN GILGER: So we could kick off some early wildfire season activity here. We’re already seeing some fires around the state right now. Are we hoping that the rains will come shortly thereafter and help things out?

RANDY CERVENY: That’s usually what will occur. We’ll have about the first week or so in July associated with these big mammoth dust walls that come in, these haboobs that come into the Valley. And then we’ll start getting more and more moisture associated with them, and we’ll have less dust storms, more thunderstorms.

LAUREN GILGER: OK, we’ll see how things shape up this year. ASU professor of geographical sciences Randy Cerveny, an extreme weather expert coming on of course to fill us in all ... on all of our latest questions.

Randy, thank you so much for coming on, appreciate it.

RANDY CERVENY: My pleasure.