Areas of flash flooding likely in southern Utah, Southwest US through the weekend

(CNN) — The desert Southwest, including southern Utah, an area dealing with long-term megadrought, is bracing for a moderate risk of extreme rainfall which could lead to flash flooding as we head into the weekend.

Nearly 10 million people are under flood watches as widespread rainfall totals of 2-4 inches are expected across Arizona, New Mexico, and southern Utah.

Showers and thunderstorms are possible today across this region, but rain chances really increase, especially in terms of heavy rainfall, Friday and Saturday.

⚠️ Flash flood threat is increasing again today across southern Utah. This threat will expand northward tonight into Friday.

If your plans include slot canyons, normally dry washes and slick rock areas in the flood watch, monitor the weather and consider a plan B! #utwx pic.twitter.com/5Hd3aS9oJv

— NWS Salt Lake City (@NWSSaltLakeCity) August 18, 2022

Zack Taylor, a senior meteorologist at the Weather Prediction Center, pointed out there are multiple factors creating the new surge of moisture, including the remnants of a tropical wave currently over northern Mexico embedded within the larger-scale monsoon.

A special weather statement has been issued for Millard County, UT until 3:15 PM MDT pic.twitter.com/WWL0sRF81p

— NWS Salt Lake City (@NWSSaltLakeCity) August 18, 2022

One thing making the particular event different is the timing of the storms. Typically, monsoon storms are diurnally driven, meaning they occur in the afternoon and early evening. This time, rain chances will be around the clock. Storms will fire up in the afternoon and early evening as usual, but will also occur Friday overnight and early Saturday morning.

On Wednesday the Weather Prediction Center issued a rare “moderate risk” (Level 3 out of 4) for Friday in preparation for the surge of rain expected this weekend.

“It doesn’t happen too often that we issue a moderate risk for excessive rainfall three days out, certainly not for the Southwest,” said Taylor.

There are also two impact timelines with the next system: the short term, which would be flash flooding, and the long term, which would be the influence on the rivers, creeks, and streams in the area.

“The main concerns with the flash flooding initially,” Jeff Davis, senior meteorologist for the National Weather Service office in Tucson told CNN. “But we’re transitioning into a situation where we may have some of the larger washes that are normally dry and some of the main stem rivers starting to see significant flows by Monday.”

By the end of the weekend, the rain will spread east into Texas, another state experiencing significant drought. By early next week, 3-5 inches of rain is possible from Lubbock, Texas, to Shreveport, Louisiana, increasing the potential for flash flooding in those areas.

Monsoon rains are helping the drought, but not enough

While the desert Southwest may not be known as a wet part of the country, this time of the year is when they are most likely to get rainfall. The rainy season helps the Southwest, but it often leads to superficial improvement.

The drought-plagued region is already dealing with a water crisis, so they need the rain, but it may not be as beneficial as you might think.

One of the concerns with the upcoming heavy rain is it is not expected to surge far enough north or west where the water is needed most: California, Nevada, Oregon, and northern Utah.

“Several large areas of improvement were noted this week, with the heaviest rains and most widespread improvement covering Arizona,” the latest US Drought Monitor details. “After an extended period of serious drought, the heavy rains have prompted broadscale improvement in monsoon-affected areas.”

The recent rains have helped, but only for some areas of the West. Roughly 70% of the West is still in some level of drought, down from 90% just three months ago. Most of the improvements have been in just two states, Arizona and New Mexico. The recent rains have helped those two states even more.

“Monsoonal rains are only a fraction of the water needs of the West,” said Chad Myers, CNN meteorologist. “That said, the recent rains have raised the level of Lake Mead by 1.8 feet over the past three weeks.”

Myers pointed out the main driver for water in this region is the melting winter snowpack, but it doesn’t mean the rainfall isn’t beneficial.

“Although the heaviest of the upcoming rain will miss the Colorado River basin and Lake Mead, plenty will still fall in Utah and Colorado directly into the upper drainage basin of the river,” Myers said.

The US Southwest monsoon officially runs from June 15 to September 30, putting the region beyond the halfway point of the season.

The recent rain in Las Vegas has brought their monsoon total up to 1.29″ marking the wettest monsoon season in a decade. However, the city is still well below where it should be at this time in the year, having received just over half of its average rainfall up through mid-August. The 1.29″ this season already makes 2022 Vegas’ third-wettest monsoon in the 21st century. It comes just two years after the driest monsoon on record back in the summer of 2020 when there was no measurable rain.

Down the road in Tucson, they’ve had a roller coaster of monsoon seasons recently. 2020 was the second-driest on record (1.62″) while 2021 managed to be the third wettest (12.79″). So far this season, a little over 2″ has fallen in the city, below the average to date of 3.48″.

Salt Lake City has had 6.70″ so far this year, but their average is more than 10 inches. It is an ever-present sign of how bad the drought has been the last few decades in the region we are celebrating getting a little more than half of what is normal.

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