SuperMonsoon Hits in the US Southwest and Northwest get a piece of it.

There’s a good name for it: SuperMonsoon.

In my previous blogs, I talked about the nature of the Southwest (or North American) Monsoon and how water vapor from the Gulf of Mexico flies around an area of ​​high pressure into the Southwest Desert from June to October. 8.

As a result, the US Southwest is typically much wetter than the Pacific Northwest in midsummer.

The Southwest Monsoon is particularly active this summer with lots of thunderstorms and unusual north and west infiltration of moisture.

Take a look at the percentage of normal rainfall over the past month.

OH. Several areas (Nevada and southwestern California) were affected by more than 800% of normal rainfall. Everyone needs an umbrella in Las Vegas!

The past week has been particularly wet, with a large amount of monsoon moisture pouring into eastern Oregon! (see below). Much of that rainfall combines with lightning, causing some fires.

This summer monsoon is associated with unusual amounts of water vapor moving northward out of the tropics.

To demonstrate this for you, below is a graph of steam anomalies (difference from normal) from June 1 to August 13. Green to red are above levels. normal. Well…a lot of oranges and reds….much higher than the usual amount of water vapor heading northwest out of Mexico into the desert Southwest! Some of them even reach into the Pacific Northwest.

With all the humidity, bringing rain and thunderstorms, the Las Vegas National Weather Service has been busy issuing flash flood warnings (see one from yesterday below)

Looking at a map of total precipitation since June 1, which only shows values ​​above 1.5 inches, many areas in the southwest have increased by more than 4 inches, with some locations reaching 5-17 inches.

Interestingly, last year was also a major Southwest Monsoon year… in fact, even more impressive than this year.

Is there a trend towards southwest monsoon rainfall? To better understand this question, below is a chart of July rainfall in Arizona over the past century.

This year, July rainfall across Arizona is clearly above normal (and the heaviest rainfall is in August), but last year there was exceptional July rain. Some really heavy rains about 100 years ago, and July 2020 was very dry. But all and all, a lot of precipitation variability but with little trend.

Some climate modeling studies suggest that the Southwest Monsoon will be drier, and others predict little change overall (dryer first half, wetter second half of summer). But considering that thunderstorms/convection produce most of the monsoon rainfall and climate models don’t handle them well, I suspect the jury is still out on the topic.

One last thing. Last year, an abundant southwest monsoon caused grass to grow, contributing to the devastating fires in New Mexico earlier this year. The Forest Service, BLM and other wildfire agencies will need to prepare for an active bushfire season next year.