Monsoon 2020

PHOENIX (3TV/CBS 5) -- Okay, let’s start with a little bit of history. There was no “Arizona” monsoon until the late 1940s when a researcher from back east coined the phrase for Arizona’s switch in wind pattern from winter to summer. He called it the Sonoran Monsoon, which I think is a wonderfully poetic name for our summer thunderstorm season.

Soon, it got kind of regular to call the summer storms “the monsoon,” and by the 1960s, folks at the weather service were trying to devise a way we could tell when the monsoon had, indeed, arrived in Phoenix.

They came up with three consecutive days of surface dew points of 55-degrees or more. That would herald the start. Contrary to what some of the young meteorologists like to say, developers of the dew point model didn’t just pluck 55-degrees our of thin air. They determined it was a good indicator showing there was 1 inch of integrated precipitable water in any vertical column of air. That was thought to be enough to trigger thunderstorms. Tucson, BTW, used a dew point of 54 to usher in their monsoon.

Three days in a row was chosen to guard against a “false” start, a day or two where the humidity might come up but not for the summer.

To be sure, there were some issues with this legacy method, as we now call it.

In a nutshell, the atmosphere is much more complicated than taking a surface reading and projecting it into the upper layers. Secondly, the method was very Phoenix-centric, or Tucson-centric, if you happened to live there. It spoke nothing of when the monsoon arrived in, say, Pinetop.

In 2008, the Weather Service decided to put dates to the season: June 15 to September 30. I support this. It's not perfect either, but it makes sense for a whole bunch of reasons. However, it did take away the fun of “waiting” for the monsoon to arrive every year.

Well, we still do on 3TV. We just call it the “onset” or “arrival” in Phoenix. And, no, as of this writing, July 13, the monsoon has not returned to Phoenix via the legacy method of dew points. But for those of us who liked to track it, it was fairly easy to get the data.

Since 2008, the Phoenix office of the National Weather Service provided dew point information on its daily climate page. You just had to go online and look it up. But last November, in the dead of winter when no one was paying attention to dew points much, the weather service removed it from their climate report because they didn’t deem dew point information important. Funny thing. The Tucson office of the Weather Service thinks its so important they keep track of Phoenix dew points, too. You can still get the information, but you have to go to the Tucson Weather Service website, and it’s a little more difficult to find.

That’s the link, You have to scroll down a bit. So why did the Phoenix remove the dew point information? I suspect it’s because they don’t like the dew point definition and are trying to snuff it out once and for all. They apparently don’t like it when folks like us who enjoy weather are having some fun.

3TV Chief Meteorologist Royal Norman always has his eye on the radar and how weather conditions might affect the people of Arizona.  He also loves telling those quintessential stories that are uniquely Arizona. With 35 years of experience forecasting weather and his vast knowledge of Arizona and its micro climates, Royal is an Arizona Weather Authority. 

Copyright 2020 KPHO/KTVK (KPHO Broadcasting Corporation). All rights reserved.


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