“The rains are here,” said National Weather Service (NWS) meteorologist Jason Laney.
It’s an early start for the monsoon season, which could produce a total of six to seven inches in the Southwest United States by the end of September, Laney said in a telephone interview. He is the warning coordination meteorologist for NWS’ El Paso weather forecast office in Santa Teresa, New Mexico.
But even a wetter-than-usual summer won’t end the region’s drought, driven by a third consecutive La Niña climate pattern that forecasts a cold, dry winter, he said.
NWS defines the monsoon season as June 15-Sept. 30, but it doesn’t usually start in the El Paso-Las Cruces region until mid-July, Laney said. This year, however, the conditions that define the onset of the monsoons were in place in June.
“We really started seeing monsoon conditions full force on (June) 21,” Laney said, when both a high-pressure air mass and rising dew point (measuring moisture in the air) were in place. The 2021 monsoon season official started June 28, he said.
But a monsoon isn’t a rainstorm; it’s a seasonal reversal of winds.
In the desert Southwest, prevailing winds are from the west and southwest, Laney said. They come off other desert regions, so they don’t produce a lot of moisture. The pattern shifts in the summer “and we begin to have more of a flow from the south or southeast,” he said. “Most of the time it picks up moisture when it happens.”
An area needs to receive at least 50 percent of its annual rainfall as a result of the wind change for it to be a true monsoon, Laney said. Since El Paso gets an average of 5.7 inches of rain during the monsoon season (59 percent of its annual total) and Las Cruces gets about 5.5 inches (57 percent), “we definitely qualify to be a monsoon,” he said.
Because “summer thunderstorms can be quite isolated,” Laney said, “the numbers only tell part of the story. So much of it is who gets what,” he said, noting that west El Paso “took the brunt” during heavy monsoons in 2006 and La Union had severe flooding issues because of last year’s monsoon precipitation.
But even with a wetter-than-usual summer this year, the region’s drought is likely to continue, Laney said.
That’s because a La Niña weather pattern is in place for the third year in a row, creating a dryer, colder winter than one experienced during an El Niño.
El Niño is the warm phase of the El Niño–Southern Oscillation (ENSO) weather pattern (winds and sea-surface temperatures) in the equatorial Pacific Ocean that impacts weather around the world. La Niña is the opposite – a cooling phase of ENSO. There is also a third, neutral phase. (“El Niño de Navidad,” a reference to the Christ Child, was given to the warm, south-flowing air current centuries ago by Peruvian fishermen because it was most noticeable around Christmas. “La Niña” [the girl] came into use sometime later to denote the opposite air current.])
Laney said existing drought conditions began in the summer of 2020, during a weak monsoon season. The Southwest remains in NWS’s D3 category, “extreme drought,” he said. Categories range from D0 (abnormally dry) to D4 (exceptional drought).
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