Record Rainfall

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The Phoenix Metro Area saw record rainfall from Tropical Storm Norbert. School of Geographical Sciences at Arizona State University climatologist Randy Cerveny will discuss the unusual weather.

Richard Ruelas: Good evening and welcome to "Arizona Horizon," I'm Richard Ruelas in for Ted Simons. It has never rained as much in Phoenix as it did today. Tropical storm Norbert dumped more than three inches of rain at Sky Harbor Airport, a new all-time record. The Governor declared a state of emergency. Here to talk about our severe weather is Randy Cerveny. I've messed up the last name -- Arizona State University climatologist. Cerveny.

Randy Cerveny: Right.

Richard Ruelas: I know weather, climatology, is a very complicated complex science so I will try to ask you as scientifically as I can: What happened?

Randy Cerveny: Well, this was our attempt to try to be like Florida, basically. We had all of this moisture associated with this drying tropical storm called Norbert, it was a hurricane along the Baja coast. That moisture was pushed right up into Arizona. There it started to interact with our topography, our mountains, and got pushed up. We had our polar system that came through from California. All of those things came together to dump tons of rain right over the Phoenix metropolitan area.

Richard Ruelas: The storm was forecasted to hit a little bit Sunday. What delayed it? And had it hit Sunday, would we have not seen as much rain?

Randy Cerveny: I think it would have been a rain-maker no matter when it happened. The timing was the critical thing. It was simply that the moisture was taking a little longer to make its way up from the Baja area into Arizona, than what we had originally anticipated. We had forecasted this storm incredibly well. The National Weather Service had warnings about this all the way into late last week. People hopefully took it into account and that saved a lot of people I think property damage and lives even.

Richard Ruelas: I guess that's the question in Arizona, we're not used to -- we're used to rain and we sort of laugh it off, it's just going to be blowing dust. What made this unusual? Even with tropical storms dying we don't see this deluge. What specifically -- you mentioned the things that came together to make it happen. But was there something that happened overnight specifically that really triggered the rain?

Randy Cerveny: Well, I think people get a misinterpretation that this was a monsoon thunderstorm. It really wasn't. It happened, so it'll be counted as monsoonal moisture. But they tend to be really localized. They hit New River or Levine, they don't hit the entire metro area. Here we had this particular mass of moisture causing havoc all the way from Goodyear all the way to Apache Junction. The entire area was experiencing rainfall like we really haven't seen.

Richard Ruelas: What made it sit over us then all those hours? Again, we do think about monsoon storms or even winter rains seem to move through fairly quickly. What made this sit for hours?

Randy Cerveny: It actually wasn't sitting, the moisture kept being pumped up. Imagine that Norbert is a giant water pump, it was just continually feeding moisture all the way up into Arizona. So that moisture when it came into Arizona was being pushed up, proceeded to dump out the rain, and then more moisture behind it simply kept dumping it out. It was like a continual loop that somebody had stuck the VCR on repeat and it kept going over and over and over again.

Richard Ruelas: We know this set the record. I guess there are two things to discuss. We'll start with the record rainfall. What did it beat?

Randy Cerveny: Well, this was the most rainfall that we have measured -- and we measure for the Valley at Sky Harbor Airport -- this is the most rainfall measured in a single day since we've been taking records, which goes back all the way back to the turn of this last century to the 1900s. We had 3.29 inches of rain occurring during that time. Of course realize we're talking about one day. But most of that rain obviously happened within a space of just about maybe 8 to 10 hours. This was an incredibly intense rainfall experience. Something that Phoenix had never experienced before.

Richard Ruelas: So what was the record before that? How far back do we have to go, 1911 I think you mentioned?

Randy Cerveny: Yes. An event occurred back in 1911 that was a two-day event so that the 24-hour period was a little more rainfall than what we had. They were up into the four inches of rain.

Richard Ruelas: A two-day event meaning overnight --

Randy Cerveny: It started in the evening of one day and finished the evening the next day.

Richard Ruelas: Sort of like how we were expecting this to go, but it started early in the morning today.

Randy Cerveny: All the rain we have that you're hearing on the news today was a calendar day. It's rain that simply happened on this Monday.

Richard Ruelas: But 1911 was a day that was overnight to the next day, and it had more rain than this.

Randy Cerveny: Right. We're actually digging in because we haven't had a reason to do this -- we're digging into the old records to try to find out exactly what happened during that time. I'm anticipating it was something similar to this one, a dying tropical storm that came up the Gulf of California and started to dump rain. We're still trying to figure that out.

Richard Ruelas: Some of the old -- recent saws with Phoenix are the rains never come, they pass us by, there's a big bubble over our city. This seems to bely that, or is this the exception that proves of rule?

Randy Cerveny: I think this was just finally the luck of the draw that we ended up getting this kind of rain. We have had the moisture from tropical storms move into the state before. People might remember back in 1997 there was moisture from an old hurricane called Nora, that was anticipated to come in and hit Phoenix but it never did. It did hit Yuma and Western Arizona and dumped five inches of rain in the course of a day in that part, but it didn't come into Phoenix. Phoenix today was the big winner in terms of rainfall.

Richard Ruelas: With the tropical storms coming, we've seen some word that storms are getting more intense, more frequent. Is this going to be an event we can predict, that when tropical storms start to die and they hit Phoenix we might see events like this? Or is it unpredictable?

Randy Cerveny: Actually for our drought situation this rainfall isn't going to help. But it does tell us that we're going to have some interesting things. This particular summer we've had a whole bunch of hurricanes out on the coast of Mexico, the west coast of Mexico. The Atlantic has been incredibly calm, only three named storms in the Atlantic so far. And anticipating that this is going to be an El Nino year, this winter we will have a warming of the Pacific Ocean, if that's the case we will have a bunch of winter storms to help us bring in more moisture. But by this winter it'll hopefully create enough snow that we'll have a really great snowpack. We're anticipating the fact that we had this storm come through is going to lead to a better winter than what we might otherwise never have.

Richard Ruelas: Because it's summer and the rain gets soaked up and washes away, what is the situation in California? They are waiting for the snowpack, as well?

Randy Cerveny: Right. This moisture made it into California, not much of it. They did have storms but we were the big winners in the southwest. If you want to think about it, we got that much rain. The problem is that it all hit so fast and hit the metropolitan area as opposed to the water, it's going to go down and not really be recovered. We need to have it occur up on the watershed so we can hold it back by the dams.

Richard Ruelas: We saw the footage of the streets flooding today. How Arizona, how Phoenix is equipped to handle rain like this, because we don't get it this often, are we ill prepared, do you think?

Randy Cerveny: That's a good question. As a climatologist I can tell you this was a really rare event. The kind of rainfall that we're seeing, we seem to use this phrase a lot this summer, but these were thousand-year events. They shouldn't happen with regularity across the metro area. It's not what engineers designed for. The fact that so many pumps were able to handle that water, not that surprising. Whether we should have to revise those, we have to see if these things are going to become more common. If they are, we might have to adjust some engineering code.

Richard Ruelas: Is that really a possibility as we see storms become more volatile, whether it's manmade or not, due to climate change, are we going to see more results like this?

Randy Cerveny: Well, the one thing that we have really kind of have a consensus on in terms of climate change, with a warming climate you get more rain, usually more intense rain. So if that's the case, it is likely that storms will become more frequent across the globe. Any one particular place, kind of hard to define that. As a globe as a whole we should get more rain around warming climate.

Richard Ruelas: You predict this winter will be a good test case to see what a warming Pacific Ocean does to Arizona's --

Randy Cerveny: Exactly. El Nino here in the southwest, we really look forward to that in terms of replenishing our water. We are hoping that warm Pacific Ocean will help us draw in lots of storms and create a very substantial snowpack.

Richard Ruelas: And for Arizona, we are hoping for snowpack in the mountains to reduce the drought.

Randy Cerveny: And recreational skiing places are really cheering that we might have an El Nino winter.

Richard Ruelas: We'll have you back, thanks so much.

Randy Cerveny: Thank you.

Randy Cerveny:Climatologist, School of Geographical Sciences at Arizona State University;

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