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SALT LAKE CITY — Federal forecasters say there's an increased risk of flash flooding in slot canyons, dry washes and areas near recent burn scars in southern and central Utah Thursday and Friday as monsoonal moisture returns to the state.
They add that flash flooding is "probable" across many Utah national parks and recreation areas because of the elevated risk.
The National Weather Service placed Arches, Canyonlands, Capitol Reef and Zion national parks, as well as Glen Canyon National Recreation Area, Grand Staircase-Escalante National Monument and Grand Gulch into the third tier of four flash-flood risk levels Thursday. The agency adds that flooding is also possible at Bryce Canyon National Park, Natural Bridges National Monument and the San Rafael Swell.
All of those areas list between possible and probable flooding Friday, as well.
Some of the risks have already materialized. The weather service issued a flash flood warning for parts of Iron, Kane and Washington counties, including Zion National Park, because of a thunderstorm with the potential to 1 to 1½ inches of rain in an hour. The warning remains in effect through 3:30 p.m. Thursday.
KSL meteorologist Matt Johnson explains that a low-pressure system over the Southern California coast is pushing tropical moisture back into the southern half of Utah, providing more scattered showers and thunderstorms. Most of the storm activity is expected to begin Thursday afternoon in southern Utah, spreading across southern and central Utah as the day continues.
"We are looking at that deeper monsoon moisture in play, so (there's) a better chance for some soaking, heavy downpours with some of those thunderstorms," he said, noting that areas south of Interstate 70 have a higher probability for these types of storms on Thursday.
Showers/thunderstorms producing heavy rain expected across southern & central Utah today, with threat increasing significantly after 11AM. This will especially impact recreation in slot canyons and normally dry washes, and bring the potential for isolated urban flooding. #utwxpic.twitter.com/YBIsI5BrqG
— NWS Salt Lake City (@NWSSaltLakeCity) August 10, 2023
Another wave of moisture is expected across the state on Friday. Johnson said that is when the central Wasatch Front, northern Utah and wider swaths of the state's eastern side are more likely to receive storms. He adds there's a slight chance the pattern continues along the Wasatch Front into the weekend, "depending on how this monsoon moisture pans out," while there's a greater chance across southern Utah.
Full seven-day forecasts for areas across Utah can be found online, via the KSL Weather Center.
Monsoonal moisture caused more of an issue along the Wasatch Front last week, though several communities throughout Utah received a "summer's worth" of rain from those storms. Draper Mayor Troy Walker declared a state of emergency after one storm caused widespread flood damage on Aug. 3.
But the moisture could help efforts to quell the Thompson Ridge Fire located 11 miles southeast of Beaver, which has quickly grown into the state's largest wildfire this season.
"Firefighters are scouting for areas to begin implementing direct and/or indirect fireline — such as dozer line, hand line and use of natural barriers that will provide the greatest opportunity to work toward (the) containment of the fire safely and effectively," the Bureau of Land Management reported Wednesday.
The lightning-caused fire has burned more than 7,200 acres and remains 0% contained, the report added.
