Horizon, Host: Ted Simons

August 30, 2010


Host: Ted Simons

Rain or No Rain?


  • Will this winter be hotter and drier, or colder and wetter, than usual? ASU Professor of Geographical Sciences Randy Cerveny shares what the weather patterns appear to have in store for Arizona.
Guests:
  • Randy Cerveny - ASU Professor of Geographical Sciences
Category: Environment

View Transcript
Ted Simons: Here to talk about the weather in the fall and winter months is ASU professor of Geographical Sciences Randy Cerveny, thank you for joining us.

Randy Cerveny: Thank you.

Ted Simons: Before we get to the forecast for the next few months, JPL and some other scientific folks have come out with a story that El Nino has doubled in intensity and warmth over the last 20 years. What does that all mean?

Randy Cerveny: Well, El Nino, first of all, the whole idea with El Nino and La Nina has to do with the center of the Pacific Ocean. Think of it as a giant hot tub that kind of sloshes from one way back towards the other way. When it sloshes towards Australia, it's sloshing cold water. When it comes back, it sloshes warm water. Over the last year we've had the warm water of El Nino. The JPL scientists are showing us that what we've had over the last 20 to 30 years, more of these El Nino events and more intense El Nino events. There is something called the Pacific oscillation which is an overarching thing that controls El Nino and we think that could be part of it. Also, it could be somewhat the effect of global warming.

Ted Simons: NOAA was also saying it seems to be shifting westward, as well. What does that mean?

Randy Cerveny: Well, the position of where this warm water is that is in the Pacific Ocean determines where our storm track is going to be. So if it's located in the central Pacific Ocean, oftentimes that storm track will come down through California and into Arizona and New Mexico. If it shifts a little towards the west, it might push more precipitation towards California and a little less towards Arizona if that holds true.

Ted Simons: Shifting means perhaps less rain, but strengthening could mean perhaps more rain?

Randy Cerveny: Right. And it's still somewhat preliminary results so I want to see exactly what's going on. We know a lot more about what individual El Ninos and individual La Ninas will do.

Ted Simons: But as far as the idea of strengthening and all this, could some sort of natural variant like global warming be involved?

Randy Cerveny: Well, the Pacific Ocean is our biggest ocean and it absorbs a whole bunch of heat. If there's an indicator of climate change, the Pacific Ocean might be the place to look to see if it's occurring.

Ted Simons: Kind of a canary in the coal mine thing?

Randy Cerveny: Right.

Ted Simons: It's said that El Nino has morphed into something else again. What does it mean?

Randy Cerveny: It means our predictability is becoming a little bit harder to come up with. Usually, every two out of three El Ninos mean wetter conditions for Arizona. We may not be able to make those kinds of forecasts long term in the future. If we can tell you in the summer what the winter is going to be like, that's very important for the economy of the entire region.

Ted Simons: The whole idea of a strengthening and shifting El Nino affecting La Nina at all?

Randy Cerveny: La Nina is the opposite condition. It's the surge of cool water being pumped up along the coast of South America and into the central Pacific. Normally that's the normal situation that we find. 8 Every five out of six years is a La Nina situation, only one out of every six or seven years is an El Nino situation. La Nina is the more common situation.

Ted Simons: We've got graphs and visuals to show, first of all, what the one-month temperature probability forecast is for the United States. It looks like a hot time here in Arizona, doesn't it?

Randy Cerveny: These are probability values you're actually seeing. They are not really temperatures but we're above normal chances for having warm conditions here in the southwest is basically what that's suggesting.

Ted Simons: And we have another graph that shows the one-month precip forecast. Again, this looks like it's La Nina all over the place because -- although, you know, it just doesn't look all that great, does it?

Randy Cerveny: No. It basically means that we're going have what's commonly called a big ridge over us for the next month that'll push the storms up to the North and into the Oregon-Washington area, instead of the southwest part of the state.

Ted Simons: Let's go to the three-month temperature graph. This is not refreshing for Arizona. In fact, it looks awful hot there.

Randy Cerveny: We're going to live up to a nice wintertime tourist type of thing of being a very mild, warm place. The ski industry is not going to enjoy this forecast. There's an above normal probability of having warm conditions over the Southwest.

Ted Simons: And looking at that three-month graph for precipitation, and it basically says, Arizona, we're going to go all around your border and you're not getting much.

Randy Cerveny: Once again, the storm track under a La Nina in this winter situation will push the storms up towards the Northwest as opposed to the Southwest.

Ted Simons: Will they push the storms north, too far north to help with the Rockies? I know there's a lot of concern about CAP water, the whole nine yards. Is it better for La Nina or El Nino?

Randy Cerveny: That's a very tricky thing to do. It basically feeds the headwaters of the Colorado River and it tends to be in that transition zone. Simply a difference of a couple hundred miles of the storm track can make a difference as to whether we get a lot of water on that watershed or not. The nice thing, we're coming off a fairly wet winter, so other local reservoirs are relatively full. But the Lake Mead, Lake Powell reservoirs are still below normal.

Ted Simons: If you enjoyed the winter with the rain, good luck, fella, this year. If you enjoy it warmer, you'll be happy with this forecast.

Randy Cerveny: That's it.

Ted Simons: Thank you for joining us.

Randy Cerveny: My pleasure.

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