Water and weather experts are fairly certain that five to seven consecutive days of high temperatures will bring widespread flooding. Less predictable, however, are mudslides and debris flows that can swallow roadways and structures with little warning.
The spate of landslides reported since Saturday after heavy rains in northern Utah is an unsettling reminder that flood season in the mountains is precarious in more ways than one. And with each passing day, the time frame for melting record amounts of snow at high elevations becomes more compressed.
If temperatures suddenly rose to normal — or above normal — creeks and rivers in much of Utah would jump their banks, according to Brian McInerney, a hydrologist for the National Weather Service.
That most likely would lead to more mudslides, too, said Rich Giraud, senior geologist with the Utah Geological Survey.
The average high temperature for valley locations in northern Utah during the first week of June is 82 degrees. But the forecast for the next five to seven days calls for relatively cool temperatures, according to the weather service, with highs ranging from 60 degrees to the mid-70s. Rain showers Tuesday should give way to partly cloudy skies for the remainder of the week.
A string of days with average to high temperatures could result in a quick melt that would continue to soak and destabilize already saturated soils, particularly on steep slopes, Giraud said.
“You really can’t forecast landslides. In terms of timing, we can’t do that,” he said. “But when we have above-normal precipitation and a lot of snowmelt, the potential increases. If it warms up, we may start to see a lot of landslides.”
Davis County, with its steep canyons, has had a history of mudslides and debris flows, including a number in 1983, a year remembered for widespread flooding, Giraud said.