Written by Meteorologist Dave AguileraDENVER (CBS4) – Our recent bout with daily drenching thunderstorms is being fueled by an annual summertime weather event: the Southwest Monsoon.

This phenomenon happens every year, but, this year it has rolled in earlier and stronger than it has for quite a while.

Monsoon is an Arabic word meaning;  “a reversal of the winds”. Another definition applied to the word is ” Season.”

The Southwest Monsoon typically begins early to mid July and runs through early to mid August. Although, depending on the year it may develop earlier or later than those dates.

There are several weather features that help to get the reversal of the wind patterns going.

First, in early summer the upper level and lower level wind flow tends to be from a drying westerly direction. As the southwest part of the nation heats up a stagnant thermal low forms over and near the Mojave Desert.

At the same time a stagnant area of high pressure forms just of the southeast coast of the United States. This high is sometimes called “The Bermuda High” because of its proximity to Bermuda. But the high can at time waffle from the Atlantic, Florida and the Gulf of Mexico.

These two features help to funnel moisture from the Mexico and the Gulf of California providing parts of Colorado and the Denver metro area with almost daily chances for afternoon showers and thunderstorms during this period of the summer.

Throughout the life of the monsoon there are periods of extreme moisture and less moisture. We call these bursts and breaks in the pattern. The burst would bring us greater chances for heavy rain and strong thunderstorms. The break period would still bring in thunderstorms but, they are fewer and weaker as slightly drier air gets into the mix.


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