A long string of sunny days in a desert town might seem unremarkable, but this year’s spell of dry weather is making some wonder just what’s happened to the regular monsoon season.
Recorded rainfall for the months of July, August, and September — the traditional monsoon season — wasn’t even half an inch. Typically, Moab receives over six times that in an average year.
It wasn’t just Moab that had hot temperatures and a weak monsoon season: Areas across the entire Southwest had record-breaking years. Flagstaff recorded its driest summer ever, as did Phoenix, and Las Vegas set a record for the most consecutive days without rainfall.
All this contributes to what is already an extended drought in the Southwest. According to the United States Drought Monitor Map, put out by the University of Nebraska-Lincoln in partnership with the National Oceanic and Atmospheric Administration and the U.S. Department of Agriculture, over 70% of Utah is in an “extreme drought,” the second driest classification. Nearly 16% percent of Utah is currently in an “exceptional drought,” the driest classification given. Utah is rapidly approaching a drought as bad as 2003, when the entire state was in an extreme drought, and between 15-18% of the country was in an exceptional drought. That being said, Utah has essentially been in a drought since the beginning of 2012, with short reprieves in the springs of 2017 and 2019. Although the main source of water for Utah aquifers is snowpack, monsoon rains add to water resources, reduce heat, and bolster crops and natural vegetation. However, the dry spell doesn’t appear to be ending anytime soon.
For climate scientists and residents, the question is ‘will this be the new normal or is this just typical seasonal fluctuation?’
“The generally accepted consensus is that warmer and drier summers are all but a guarantee,” said Michael Charnick, the lead meteorologist for the National Weather Service’s Grand Junction office. “But what’s still uncertain is the extreme level. Are they all going to be quite as dry as this one, or is it going to be more of a gradual trend?”
How Monsoons Work
During the winter, southern Utah typically sits in a high pressure bubble, keeping the winters relatively mild. As the spring comes and as the desert heats up, that bubble moves northward and is replaced with low-pressure areas drawing moist air from the Gulf of California and the Gulf of Mexico. As the wetter air masses get pushed up and over the mountainous regions of the desert they lose their moisture via thunderstorms, or what typically is experienced during the summer months of July, August, and September: monsoons.
Southern Utah has also received occasional supercharged monsoon storms in late September or even early October due to moisture injections from the remnants of tropical storms off the Pacific Ocean or, occasionally, the Gulf of Mexico. These storms can feel like punctuation at the end of a monsoon season—one last big dump of moisture before the region’s typically stable, dry autumns.
For the past few years, though, this pattern has been significantly weaker than normal. A high pressure bubble has continued to sit over the Four Corners area like a rock in a stream, forcing moisture around it, Charnick explained. Instead of local rainfall, moisture instead gets forced west of southern Utah, into Nevada and the Great Basin, or east as far as Texas. However, in some years the high pressure bubble might settle elsewhere, he said, allowing the monsoons to flow from the Gulf of California through Arizona straight to Utah.
Patterns of the Future
The future of the monsoon in southern Utah remains uncertain, experts say.
According to the most recent International Panel on Climate Change report, considered the scientific consensus on climate change, the North American monsoon has seen two seemingly contradicting trends in the past fifty years: fewer monsoon storms, but more intense storms when they do arrive. According to the report, various predictive models suggest a reduction in monsoon activity but that outcome hasn’t been consistent across all models. What has been consistent is higher average temperatures, which will likely coincide with more frequent extreme temperatures, and longer stretches of consecutive dry days.
“The monsoon pattern, it depends on a lot of different things ... so you can have back-to-back years with limited monsoons and then have a large monsoon the next year. It's not indicative of a long-term trend,” said Christine Kruse, a meteorologist from the Salt Lake City office of the National Weather Service.
With scientists pointing to an already-changing climate, studies show that complex weather systems may shift to give us less frequent but more violent storms. The IPCC report presents strong arguments for expected increases in the frequency and severity of tropical storms, particularly in regards to increased rainfall amounts. It is these tropical storms that result in large, late-season storms in early autumn in the Southwest.
“We do occasionally see remnants of eastern Pacific hurricanes and tropical storms that make their way up into eastern Utah and western Colorado. In fact, we had one or two last year that really helped us out moisture-wise,” said Charnick.
There are other, more subtle side effects of the frequent dry monsoon seasons. Desert soil is so dry it doesn’t release as much moisture into the air at night. Even though Moab has seen warmer than usual daily highs, temperatures at night have not risen to match, since there is little nightly humidity preventing the heat from radiating off. That same lack of moisture drives higher daily temperatures, however, since there’s no moisture to absorb the solar energy during the day.
Climate change predictions rely on complex models with a huge amount of variables. Different models can contradict each other simply by altering seemingly small inputs and forecasters say it’s unclear what next year may bring.
“Just because the monsoon was drier this year doesn't mean that people shouldn't be paying attention to the weather before they go out next summer, especially if they're gonna go into a slot canyon or a place that would be exposed to flash flooding,” cautioned Kruse. “Don't use this year as an extrapolation for what you do next year.”