Published 5/5/21 4:15 am
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The last couple of years I did not post any type of Monsoon outlook. Ever since I moved to Colorado nearly 30 years ago I have heard about the Southwest monsoon. Being a meteorological nerd, it never sat well with me. I have always thought that the version of the monsoon we get in Colorado is an indirect by-product of the actual southwest monsoon which affects Arizona, New Mexico, and portions of Texas.
The best formal definition I have read of the monsoon is as follows:
“The North American monsoon happens once a year, usually in the middle of summer. Warm, moist air from the Gulf of California blows northeast, while warm, moist air from the Gulf of Mexico blows northwest. These two winds meet over the Sierra Madre Occidental mountains in central Mexico. The monsoon brings moisture to the mountain ecosystem before continuing north to the U.S. states of Arizona, New Mexico, and Texas.” This was from National Geographic.
Notice, they don’t mention Colorado in that definition. Over the years, it has been a losing fight to call the “monsoon” in Colorado anything other than the monsoon. It is too ingrained in people’s minds. So if it is not the monsoon, what is “it”?
In my opinion, the southwest monsoon is a result of the increased moisture that flows out of those states into Colorado. The moisture combines with daytime heating and increased convection. This results in moderate to heavy rain and thunderstorms. Some meteorologists that share my opinion call these high heat-based thunderstorms.
I have a similar line of thinking when it comes to named tropical storms. When a hurricane or tropical storm makes landfall, then travels inland a couple of hundred or more miles and becomes a tropical depression, they are no longer a hurricane. Yet, if you watch weather TV, they continue to call it by its named status for days after landfall.
A good example of this was Tropical Storm Bud. The remnants of this storm in June of 2018 finally brought some relief to our area during the 416 fire. News stories all talked about how Tropical Storm Bud slowed the progression of the fire. In reality, it was the remnants of the storm which fueled heavy rains over the area. It was not the storm itself as it was originally named.
Here was the last position of Tropical Storm Bud according to the National Weather Service.
Speaking of tropical storms, they also contribute indirectly to the “monsoon”. If you asked a dozen people about last year’s hurricane and tropical cyclone season, I bet every person would answer that it was one of the worst on record. This is only partially true. The Atlantic hurricane season was by far not the worst season on record but it was above average. It got a lot of attention. What you may not know is that the Atlantic tropical season is a small portion of the global tropical cyclone season. The Pacific is king when it comes to tropical cyclones. Last year was one of the lowest ranking Pacific tropical seasons ever. The southwest US relies on remnants of a couple of recurving tropical cyclones per year for precipitation. We got no relief with that last year.
The Euro model is known as the ECMWF. It is not only a model, it is Europe’s equivalent of our National Weather Service, The European Centre for Medium-Range Weather Forecasts.
In addition to the model I always reference in my updates, which is updated 4 times per day. It also has a weekly model which updates twice a week and a seasonal model which updates monthly. While I have my frustrations with the short-term Euro model when it comes to light precipitation events, the long-range weekly and seasonal models are much more accurate when it comes to precipitation trends than any other model I have seen. Since February, the seasonal model has been indicating above-average precipitation anomalies for our area for June-August and July-September. Not only for us but for much of the southwest US.
The green areas indicate above-normal precipitation. The white areas show average precipitation. The brown areas indicate below normal precipitation.
Here are the anomalies for June-August.
Here are the anomalies for July-September.
If you break this out by month it shows average precipitation in June, above average for July and August, and slightly below average for September.
Whether you want to call it the monsoon, the nonsoon, or high heat-based thunderstorms, this model says we are going to get more of it this year.
When we have one, our rainy season usually starts around the first or second week in July. Because the model is showing positive precipitation anomalies for July and August I would say that we are going to have an above-average “monsoon” season!
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2 thoughts on “The Monsoon Outlook–First Look”
Thank you for your timely and optimistic treatise on the “monsoon” phenomenon here. It helps to allay some fears of a horrible wildfire season….but we shall see. Meanwhile, I will perform as much mitigation as possible around my buildings. We are only talking about computer models, after all.
Thanks for that great explanation of the monsoon! Sure hope that forecast is right. Our ranchers and farmers are In a bad way! You do a great job!