National Weather Service meteorologist Michael Bruce talks about the new set of data the agency is using to calculate normal temperatures.
Ted Simons: When it comes to the weather, Phoenix will soon have a new normal. The National Weather Service calculates normal temperatures and rainfall based on a 30-year average. Starting Monday, a new range of years will be used in the calculations. Joining me now to talk about this change in the weather is Michael Bruce, a meteorologist with the National Weather Service in Phoenix. Good to have you, thanks for joining us.
Michael Bruce: Thank you.
Ted Simons: Again, they change next week because a kind of rolling 30-year average we're talking about here?
Michael Bruce: Yeah, we did. You know,many years ago the powers that be decided as we define the climate of the country that we'd needed kind of some type of standard to define the normals, and they arrived at 30 years, so each decade we'll update the normals, and we'll always see a little bit of change.
Ted Simons: So next week, starting Monday, everything that happened in the 70s: out. Everything that happened from 2000 to 2010: in.
Michael Bruce: Correct.
Ted Simons: What does that mean?
Michael Bruce: It means that our normal temperatures are going to increase by maybe about .9 of a degree over the course of the year. Our Normal rainfall is going to decrease by little bit: we were average rainfall I think 8.29 inches; we're going to go back down to--I believe it's 8.03. What's interesting about rainfall even still--if you go back through the decades and look at the long term average, that's just a little bit over 7.5 inches. So our new normals on the rainfall are still going to be a little above the long long-term averages.
Ted Simons: And I was reading--the 1970s were considered pretty wet decade. That's when we had the 100 year flood every couple of years, wasn't it?
Michael Bruce: Well we did have some major events. The 70s were quite active. As a matter of fact, an event I personally saw was the tornado in Tempe in 1971.
Ted Simons: There we go.
Michael Bruce: And shortly after that, we had the worst flash flood in Phoenix history in June in 1972. And what made that so interesting was the fact that June is our driest month of the year, but you had to produce the worst flash flood.
Ted Simons: Well it's interesting you bring that up ‘cause that one incident--I think at the airport they had close to two inches or something like that. But that one incident can skew that month which can skew that decade which can skew the 30-year average, can't it?.
Michael Bruce: Exactly. And That's part of the living in the desert: I mean the desert extremes. If you're in a climate where the average annual precipitation is 60 inches, you'll notice that percentagewise you'll be fairly close to that every year. If you're in a dry climate, arid climate, you could have tremendous swings and precipitation from year to year.
Ted Simons: Now we're seeing July. Correct me if I'm wrong because I was kind of looking at the graphs, and there are a lot of graphs and numbers and things. It looked as though fall and winter: hotter, drier, but the summer pretty much the same temperature and maybe even a little letter? Is that relatively accurate.
Michael Bruce: Well, relatively. You know, with the precipitation, I wouldn't, you know, put too many chips on that.
Michael Bruce: The biggest thing that affects the Phoenix Climate is the urban heat island. As a matter of fact, if we go back and throw the ‘70s out, back in the ‘70s, there was a little bit of distance between Phoenix and Tempe, Tempe and Mesa and Mesa and Chandler and so on. But now we have Sky Harbor right in the middle of the urban heat island; that has a lot of effect on what's going on. As a matter of fact, if you go back and look at the records in the 70s, you'll see we had quite a few freezing temperatures at Sky Harbor airport during the 70s but since 1980, only a handful.
Ted Simons: But that also means significantly higher low temperatures--higher nighttime temperatures?
Michael Bruce: Yeah, it does. Remember the old Cowboy moves, and he had the fire and the stones around the fire, and they kept him warm all night. We've got all this concrete and asphalt and that's what's going on here.
Ted Simons: We will see more of that represented in the new normals because in the 70s, you can drive from Tempe to Chandler and hit some open fields out there.
Michael Bruce: Exactly. I kind the believe this will be the last time we see a major adjustment because of that. Since the 80s we've all been on one big megalopolis with Sky Harbor in the middle. I think the signal that we'll see from the urban heat island will be quite a bit less than what we're seeing this time.
Ted Simons: So we're seeing average temperatures up, especially in spring and fall?
Michael Bruce: Spring and fall, right.
Ted Simons: And as far as nighttime temperatures all years round? Are we going to see a 100 degree low here, do you think?
Michael Bruce: It'll probably happen sometime, but things have to just right: we have to have a layer of clouds come in overnight and hold the temperature up. That's what they will do. The clouds will make temperatures warmer overnight. A lot of things would have to come together to make that happen. The benchmark right now is 96. But one day it's certainly possible.
Ted Simons: I'm not sure it is. Also the idea of spring and fall being a little warmer on average. Does that mean the hotter temperatures, if you will, start earlier, last longer in the year?.
Michael Bruce: Perhaps, but again, I think you're looking at the urban heat island if that's a product of that. I think if you got out in the desert outside of Phoenix, you wouldn't see that big of a signal. Again, we're talking with temperature changes in a few tenths of a degree.
Ted Simons: So we're not going to see nightly newscasts anymore where it's always, always above the average. Maybe now we'll start to get closer to the average.
Michael Bruce: That's the difference between climate and weather: weather can do a can do a number on climate sometimes.
Ted Simons: There you go. Compare what's happening here with other places around the country. Seeing similar things?
Michael Bruce: Interestingly, I guess the biggest thing, they came from the northern plains, Minnesota, where average low temperatures took a huge jump. If you went through the mid-Mississippi valley areas and into the southeast, some of those places saw lower high temperatures. Overall the normals have increased in terms of temperature. Precipitation-wise, I don't think there's much of a signal. Climate is constantly changing; changes to the normals are our normal. That is normal.
Ted Simons: There you go. As far as long-term climate models for Arizona, what are you seeing? What's out there?
Michael Bruce: Well I'm not an expert in that area. and I hate to venture a guess, but there's a lot of different theories on there. If indeed the globe is warming, how that would affect Arizona over the long term. You know, and I've seen these theories in other places, other parts of the country too. And my answers is I don't think we know.
Ted Simons: But we do know if development continues, that urban heat island affect that will--and that also affects weather as well because you hear about storms going right around the Phoenix area because of the heat island.
Michael Bruce: Okay, that's a myth.
Ted Simons: Is that a myth?
Michael Bruce: That is a myth:
Ted Simons: That's beautiful; that's a myth, okay.
Michael Bruce: That's a myth. You know, we did several studies. One of the gentlemen in the office did a study on it. I kind of think where that came from, back years ago the metro area was a lot smaller.
Ted Simons: Right.
Michael Bruce: You had a storm and it affected a lot of the valley. Now the valley's so bit that that most events do not fact the entire valley. We'll have one in the east valley; we'll have one in the northwest valley, and so on. Again, you have to look at things with a real long term when it comes to climate.
Ted Simons: Well I can't bore people with that story anymore, huh?
Michael Bruce: No--well, sure.
Ted Simons: I guess so. Hey, thank you so much for joining us.
Michael Bruce: Thank you very much.
Ted Simons: And that is it for now. I'm Ted Simons. Thank you so much for joining us. You have a great evening.
Michael Bruce: National Weather Service;
