12:35 PM, Wednesday, July 19, 2017
The North American monsoon, sometimes called the Southwest monsoon or the Mexican monsoon, is a seasonal weather pattern that in some years can bring enhanced rainfall across the southwestern U.S., including the Front Range region. The impacts for the Front Range are seen in the climate record from mid July through the late summer. In a nutshell, showers and thunderstorms erupt daily along the Mexican Sierras as the tropical Pacific heats up and that pumps lots of moisture into the atmosphere. Some of that moisture makes its way north into the southwestern United States. In the Front Range region not every year sees the effects, and the surges of moisture can be intermittent.
The 2017 monsoon has arrived, but for the most part the moisture has been in the upper levels of the atmosphere and so rainfall has been sparse despite afternoon clouds (there has been more moisture and areas of rain from Colorado Springs southward). Over the next two or three days a moderate plume of moisture (mainly middle and upper levels) should result in some afternoon and evening showers and thunderstorms. It’s not a highly anomalous amount of moisture, but it’s the best we have seen in a while. The best chance for rain is over the mountains of western Colorado, but I am holding out some hope for the Front Range too.