Monsoon Season

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National Weather Service meteorologist Gary Woodall talks about the start of Arizona’s monsoon season.

Ted Simons: No thunderstorms in sight but according to the calendar, monsoon season starts tomorrow. Here to tell us what to expect is Gary Woodall, a meteorologist for the national weather service in phoenix. Good to have you here.

Gary Woodall: Thank you, ted.

Ted Simons: Why are we start, the monsoon on June 15th when it almost never ever rains?

Gary Woodall: For many years, we tracked the start and end of the monsoon by the trends of the dew point. For the start of the monsoon, we looked for days where we had an average dew point of 55 degrees for three consecutive days. That was a sign that the moisture was moving up and the moisture was in place. What we found, though, is that people were focusing more on when was the season starting versus getting prepared for the season. And the hazards and the dangers that we can face during the monsoon. So much like the coastal regions do with hurricane season, which has a specified beginning and ending date, we followed that pattern, and adopted June 15th through September 30th for the monsoon so we can focus more on the preparedness and making sure that we are ready for whatever the season holds in store.

Ted Simons: What do we need to be ready for? Talk about the dangers and the hazards.

Gary Woodall: Monsoon season brings a variety of hazards here in the vale and across Arizona. Lightning which is the number two killer from thunderstorms, of course, our storms are known for producing a lot of lightning when they move through. Flash floods which are the number one killer associated with thunderstorms and most of those flash flood deaths occur in vehicles, people driving across flooded areas and the water is deeper and more powerful. This year we are going to have an extra threat from flash flooding and that was the, that is the burn area from the sunflower fire which occurred up along the beeline up in Payson. A very large area of steep terrain and much as we saw following the Schultz fire and the Walla fire last year, that will be an area we focus on for a lot of runoff when the storms move through and a lot of water coming down through Sycamore Creek area. And then dust storms, of course, with the storms that we get, they produce a lot of wind, damaging wind in some cases, and if they move up from the southeast, from the Tucson or casa Grande area, they tend to pick up a lot of dust and move into the Casa Grande area like we saw last year.

Ted Simons: That is where the dust comes from. We were talking about how it's interest you can get south of Tucson, even Casa Grande, the dust storms are not nearly as severe or frequent. It's that huge expanse north of Tucson. That stuff just comes rumbling up here, doesn't it?

Gary Woodall: The storms that generate our dust storms, the thunderstorms that generate our dust storms tend to originate generally in the Tucson area. The peaks around Tucson or the higher terrain off to the west of Tucson, and as those thunderstorms intensify they produce the strong, local winds that will generally push downhill, push down towards us in the valley, roar across those flat open areas where a lot of agriculture also takes place. And it's just a prime setup for that dust to be picked up and blown into the area.

Ted Simons: So when does, when would you think, when does it usually happen? We get that third 55 degree dew point. When do the storms, it seems like it's always after the 4th of July.

Gary Woodall: Generally, around the first week to 10 days of July is when we traditionally look for the activity to start to pick up, and we certainly saw that in 2011 with a very active first week or so of July. Some thunderstorms down in the southeast valley and, of course, the huge dust storm that occurred July 5th, I believe it was, of last year. So typically around the first week to week and a half of July is when we look for things to really ramp up here in the valley.

Ted Simons: What kind of monsoon can we expect this go around? Or I have heard this before, can you even predict that kind of thing?

Gary Woodall: It's really difficult to tell for sure, ted. Because unlike the wind season, which we have very large other scale weather features that drive our rain and our weather pattern, El Niño and La Nina, during the monsoon it may be very small-scale features, things that are very difficult to forecast more than a couple of days in advance, and in some cases, it's not until the day of an event that we see all the ingredients coming together. So it's really difficult to say for sure exactly how active it's going to be. But a couple of things that we are confident about. Number one, we will have storms. We will have dangerous weather. And so we do need to prepare for that. And in all likelihoods at least the first rounds of storms we get will be rather dusty as well since it's still very dry down in that breeding ground that we talked about in the southeast and south central Arizona.

Ted Simons: If we are going to get early storms we should hope some of those early storms hit the Tucson area and the Casa Grande area before they come up here.

Gary Woodall: Hopefully they will drop a lot of rain in that area and get the dust kind of wet down. Once that happens, usually the dust storms become a little less of a threat for us. Last year, though, we never really got the widespread rain across the area. And that's why we were dealing with so many dust storms even through the later portions of the season.

Ted Simons: The idea of having to have crazy hot temperatures before the storms move in, it seems like every year, we got to get to 115 to 120 in that range and all of a sudden over the Horizon come the clouds. Is that, is there some sort of pattern there?

Gary Woodall: That is sort of the progression that we will often see. And, in fact, we will probably see some very hot temperatures next week in the valley. What often will happen is an area of high pressure in the mid atmosphere, maybe three, four, five miles up in the atmosphere, will develop over the southwestern U.S. and with high pressure that is when we tend to get our very hot temperatures. As we evolve into the monsoon, that high pressure area will shift off to the east a little bit. And that will, we have clockwise flow, clockwise winds that blow around the high. So as we get on the west side of that high, that is what will tend to pump the moisture up into the area, and bring the on set of the monsoon. Now, we will have to see if that's how things play out for 2012. But typically that is what we will see, and our hottest temperatures typically late June, just before the moisture starts to arrive.

Ted Simons: All right. Very good. As far as predicting these storms and having any kind of idea how long the activity will be or what the activity is, just can't do it?

Gary Woodall: It's as far as meteorology is concerned thunderstorms are very small scale, short-term. Be aware on days when we are expecting a more active day, because the storms may move in in a hurry, so be alert. Be prepared. Be ready to move to safety as storms threaten you.

Ted Simons: Thanks for joining us.

Gary Woodall: My pleasure, ted. Thank you.

Gary Woodall:Meteorologist, National Weather Service;

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