What causes a flash flood in Southern Utah?

Weather

Courtesy: Zion National Park

SOUTHERN UTAH (ABC4) – The flash flooding that struck Zion National Park and much of Southern Utah earlier this week was quite the sight both while it was unfolding and in images shown after the fact.

Tons of dirty brown water flowed through the park, with dramatic video of the heavy rain and what seemed like a raging river cutting through the parking lot area captured and shared on social media.

When the rain finally let up, photos of roads, sidewalks, and cars caked in inches of mud were also especially captivating.

Even though the state is in the midst of what could be the driest and hottest summer in recorded history, heavy rain and flash flooding wouldn’t be uncommon at this time of year, according to ABC4 Chief Meteorologist Alana Brophy. Brophy says these kinds of extreme weather occurrences should be expected.

“This is severe weather season for Utah,” Brophy explains to ABC4.

Even though one would think heavy rain would alleviate the drought conditions, Brophy says that the previous dry seasons have set this year’s extreme status in motion for a long time coming. Last summer was especially dry, and the snowpack in the winter was also below what was expected or needed, she affirms.

“We still have very severe drought conditions, so even with severe weather moving in, that does not eliminate the drought, it doesn’t even really make a dent,” Brophy says. “We need so many more days of storms to see progress on our drought.”

The current monsoon season, which is commonly thought of as a rainstorm when it actually refers to a reversal of winds, coming from gusts originating from the Gulf of Mexico played a major role in this week’s downpour. The winds from Utah’s southern neighbors brought storms from New Mexico into the state, and the mountainous terrain of the Zion National Park area forced unstable, hot air to rise and create a thunderstorm, which resulted in a large amount of rain being dropped.

Brophy, who has lived all over the state, says that thunderstorms in the southern part of Utah are quite common this time of year. Combined with the slick rock geography of the region, the canyons were flooded as the water attempted to reach the lowest point of the land.

Flooding that also struck the Grand Staircase and Kanab areas came similarly.

Another big factor that contributed to this week’s flooding and will likely contribute to future flooding was the lack of soil moisture to handle the rain. Brophy explains that the dry sand in the park doesn’t lend well to absorbing the rainfall, and as a result, the powerful mudslide that picked up debris and rocks took place.

As for whether residents and visitors to the area can expect more flash floods, Brophy exclaims “100%.”

“Thursday, it’s possible at Bryce, probably at Grand Staircase, Capitol Reef and as well it’s possible at Zion,” she says, giving a quick forecast for the days ahead.

A former resident of St. George and a fan of spending time in Southern Utah’s natural wonders, Brophy says that when she or others see a probability or possibility of moisture, it’s best to stay inside and leave exploring outside for another day.

“Anytime you see anything other than not expected, you cannot safely recreate in the terrain down there, because a thunderstorm can develop very quickly and drop a lot of moisture in a short amount of time and if you don’t have an exit plan or you’re not prepared you can catch yourself in a really bad situation,” she cautions. “So, in any place that has the chance of a storm, you would not find me recreating on a day like Thursday, even with all the sunshine.”

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