The case for a new monsoon

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It's time to re-define the Arizona monsoon, our summer thunderstorm season. It's time to set specific dates, on the calendar, which indicates the monsoon "season" has arrived and ended. It's time to forget about dew points and the endless debate over whether a storm "is or isn't" part of the monsoon. It's time for the definition to apply to the entire state. It's time to simplify.

First, a bit of history: the term "monsoon" as it applies to the desert Southwest is generally accepted by most meteorologists and climatologists, and is sometimes referred to as the North American monsoon because the monsoon is actually more noticeable in Mexico. It represents the seasonal shift of wind in the upper atmosphere from westerlies (most of the year) to a southerly or easterly flow. Before the 1960s, no one had identified the Arizona summer thunderstorm season as a regional monsoon. We just had summer thunderstorms.

Over the years, researchers noted, using upper-air data, that there were several conditions that make thunderstorms more likely during the summer months. Those conditions, they also found, roughly translated to a dew point at the surface in Phoenix of 55 degrees. One presumes they were looking for a surface "translation" of their upper-air data because before the 1960s, regular upper-air soundings were non-existent. Dew points, however, have been around for hundreds of years. What they found was a climatological way of comparing past summer thunderstorm seasons using dew points.

The use of the term outside of the meteorological community doesn't seem to be clearly understood. Though it is a season, many still incorrectly refer to individual thunderstorms as "monsoons," as in, "Another monsoon is rolling into town." What is clear is that people liked the word monsoon. It was more interesting, one supposes, to call our summer thunderstorms something instead of just thunderstorms.

The late 1970s into the 1980s were years when the term started to take off. By the time we moved here in 1981, (We drove into town during an August dust storm.) the term was in use. And as all newcomers, I remember asking: How can Arizona have a monsoon?

To many, the monsoon has become a monster. When is the monsoon coming? Was that a monsoon storm? When will it end? What does it all mean anyway? One of the problems with the current definitions of the monsoon is that it relies on dew points, the very thing that gave it some legs. That's because a monsoon is officially declared "started" only after we have three consecutive days in Phoenix with average dew points of 55 degrees or more. Obviously, the folks who developed the system weren't intending it to be used as we do today because they didn't care if we had to wait three days to decide whether the monsoon had begun. But just ask the folks at the Weather Service exaclty how many calls they get when Mother Nature is working on starting the monsoon. I bet they get hundreds of calls a day asking if, indeed, it's started.

We, in the media, eagerly count "monsoon days" and tabulate the "monsoon breaks." It's as if we don't have enough to describe in our summer thunderstorm without doing this weird, "yes it is, no it isn't" game all summer long.

And when it ends, it's also the poor dew points that come in to play. But to end it, a study of the upper air wind is also used before the Weather Service will declare the monsoon over. One local climatologist said he used to just "eyeball it" to figure out when it ended. That isn't very satisfying, is it?

And did you know Weather Service at Tucson uses a dew point of 54 degrees to determine its monsoon? Did you know the Weather Service office in Flagstaff makes no effort to define the monsoon?

I say if it's a season, which it is, and if it impacts the entire state and region, which it does to differing extents, it's time to treat it like a season and give it dates. One of the ideas is to begin the monsoon "officially" on June 15, and end it on Sept. 30, each year. It would be our monsoon, our summer thunderstorm season. It's simple. It says what it is. And it works. And we have a great example already in use: the Hurricane Season.

The Atlantic Hurricane Season runs from June 1, through Nov. 30. What does that mean? It means that's the most likely time for hurricanes to form in this region. During that time there are more likely and less likely times. And hurricanes can form before and after the season ends. But it's a way of telling a region of the U.S. that it is time that a certain type of weather could, at some point, some into play. You don't have to have a hurricane to start the hurricane season. You could have none. Or you could have too many, as we saw a couple of years ago. It doesn't mean my city will get hit. There are no guarantees. It's a season. And with that season comes the potential for hurricanes. But hurricanes are neither exclusive nor inclusive to this season.

So if we go to a system that just calls a season a season, we know it's time for summer thunderstorms. It doesn't mean it has to storm. It doesn't mean it will storm. It doesn't mean a thing except that there's an increased chance for thunderstorms in the region. (And, yes, New Mexico, northern Mexico and west Texas are part of the same deal.)

This system is simple to understand and explain, makes sense meteorologically and in no way limits anyone who is in love with the current dew-point system. If you want to count days, count them. If you want to say dew points have reached the 55 dew point threshold for three straight days, do it. If you want to compare this year's monsoon to previous ones using that information, more power to you. This new definition does not in anyway hinder you. But you must remember when you're counting monsoon days, you're counting them for the Valley only, leaving out the rest of the state. Which is another argument for the dates: It will include a state, several states, or even a region. Can you imagine how confusing things would be in the southeast if, say, Miami's hurricane season started on July 23, while New Orleans started Aug. 12, and Wilmington, W. Va., started their hurricane season on June 12?

And let's face it. When it comes right down to it, the monsoon isn't about dew points at Sky Harbor Airport. It's about rainfall, lightning, and the potential for severe weather statewide.

The folks at the local Weather Service offices are discussing this idea. And while I'll let them voice their opinions over the coming months, I think most of them like the idea. It just makes sense.

I'd like to hear your opinion. You can respond to this blog and we'll post the responses. I'll also forward your opinions to folks at the Weather Service offices in our state.