The monsoon is delivering desperately needed rain to the Southwest

WEATHER NEWS: The monsoon is delivering desperately needed rain to the Southwest

For about three months every year, the Desert Southwest turns into a magical landscape of pastel hues, arcing bolts of electricity and oases of life in an otherwise sandy, cactus-studded chaparral. Some communities pick up half of their annual rainfall in a few short afternoons, while others flood as dry arroyos transform into gushing rapids.

The culprit? The Southwest monsoon — a seasonal wind shift that pumps both Gulf of Mexico and Pacific Ocean moisture northward to New Mexico, Arizona and parts of Southern California, Nevada, Utah and Colorado. The surge of humidity brings scattered thunderstorms that roll across the region, with high cloud bases affording spectacular views of pinpoint lightning strikes. This year’s monsoon is off to a swift start, coming weeks ahead of schedule and with a greater intensity than anticipated.

A rare lightning barrage jarred California with 66,000 strikes

With the elegance and beauty comes concern about flash flooding and debris flows, particularly on the burn scars of wildfires that have impacted the Southwest in recent years.

A busy start to monsoon season

As the busy start to the season begins, Chuck Jones, a senior meteorologist at the National Weather Service in Albuquerque, said there are still months to go in the monsoon.

“It began on June 17, which is close to two weeks early,” he said in a phone interview. “Generally, we talk about the onset near July 4 and going through at least Labor Day, but we have an official monsoon season that runs from June 15 through September 30. It was early and consistent.”

One way to diagnose the monsoon is by looking at dew point — a measure of how much water is in the air. In Albuquerque, the summertime average is 47 degrees for the dew point. It soared above that in June and only recently dipped again.

“I noticed that our average dew point yesterday was down in the 40s,” Jones said. “The last time our 24-hour dew point average was under 50 was June 16. That’s 20 straight days.”

Heavy rainfall and flood concerns

With the souped-up atmosphere has come plenty of rainfall. Albuquerque picked up 2.38 inches of rain since the monsoon began June 17. The average for the entire month of June is 0.57 inches.

Albuquerque’s mean annual precipitation is 8.84 inches, meaning that more than a quarter of the city’s annual rainfall came down during a two-week window.

“A good part of the western and central portion of [New Mexico sees] 50 percent or higher” of their annual rainfall from the monsoon, Jones said. That has been a blessing in disguise for a drought-stricken state gripped by its desperate need for water. “This year’s been amazing. Most of the state improved one drought category.”

While the rainfall is welcome, it can cause issues — particularly when it all comes at once. Even a half-inch of rain per hour can be problematic for sandy soils that struggle to absorb excess runoff.

“You know what, the first 10 days to two weeks, it consisted of not convective, but more light to general moderate rain, and that helped a lot of places,” Jones said. “That didn’t harm to much of a degree the recent burn scars.”

He said that things have changed in the past week or so, and that the precipitation is increasingly convective in nature — or made up of showers and thunderstorms with torrential downpours.

“In the past week or so, it’s turning into a more regular monsoon with bursts of moisture riding up and rounds of storms in the afternoon and evening,” Jones said. “They weaken overnight and are usually done by the next morning, but we start up by noon and do it all over. But we have some issues with burn scars and flooding, mainly in the past 10 days.”

Since the start of the monsoon, his office has issued 47 flash flood warnings.

While the bulk of the monsoon’s influence thus far has been relegated to the Land of Enchantment, Arizona has gotten in on a bit of the action, too. Phoenix saw 0.32 inches of rain during June, which sounds unimpressive, but consider that 0.02 inches is the monthly average.

Farther to the north and west, monsoonal moisture at the mid-levels of the atmosphere has helped brew a few storms, but a dry near-surface layer evaporated much of the rainfall before it hit the ground. The result? A barrage of “dry thunderstorms,” a few of which produced lightning that ignited new wildfires.

More than 60,000 lightning strikes illuminated the skies over Central and Southern California during the penultimate week in June. One of the strikes killed a woman walking her dog through a park in the Los Angeles metro area.

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