State of the North American Monsoon

The North American monsoon, a seasonal weather phenomena which tends to bring beneficial summer rains to the Desert Southwest and the Southern Rockies, has been active this year across much of Colorado. This has been evident in the showers and thunderstorms which have visited Nederland and the surrounding Front Range Foothills communities in July and early August. But how does this summer’s monsoon compare past years?  So far this water year, we have received 19.16 inches of rain at our house in Nederland. That is for the water year – which runs from October 1, 2018 through September 30, 2019. Assuming the summer monsoon normally runs from June into August, then total rainfall for these three months by year is:

June, July, August

First, it is important to note that August 2019 is not over yet. Second, even though this summer has felt wetter, it is actually about the same as the summer of 2018 (so far). In fact, the number of days with measurable rainfall is nearly exactly the same between the summers of 2018 and 2019 – 28 days.  However, the monthly distribution of rainfall between this summer and last summer is slightly different. It has rained more this year in June and July than last summer. August was a wet month last year. If it seems like you have been cutting (or weed whipping) your grass more this year, it could be because June and July have been wetter this year.

Looking at the above table, notice that 2011, 2012, and 2013 were extremely wet monsoon seasons here in Nederland. Also, note that 2016, the driest summer, was also the year we had the Cold Spring Fire. While the dry 2016 summer did not cause the fire, drier fuels resulting from a lack of rainfall did help promote the growth of the fire.

Weather observations are important for many reasons. People’s perceptions and memories of past weather are very unreliable. For example, before I did this study, my perception was that last summer was much drier than this summer. Looking at the numbers, that is not really an accurate perception. The same can probably be said for people who say, “it snowed a lot more when I was a kid”. Would observations really support that? Or do people tend to forget dry winters and remember the snowy ones?

Another round of showers and thunderstorms is expected across the Colorado Mountains on Saturday and again on Sunday afternoon before drier and warmer weather returns for next week.


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