National Weather Service hydrologist Brian McInerney said fire-scarred mountain slopes will almost certainly unleash debris flows if the rains continue for days or turn heavy.
He said the light rain could fall across much of Utah for another two days.
Rain and cooler temperatures helped crews hold fire lines on the 8,200-acre Shingle fire about 30 miles southeast of Cedar City. It threatens 550 cabins or summer homes in Dixie National Forest.
Meanwhile, up to a quarter-inch of rain fell on the Clay Springs, which has blackened more than 160 square miles east of Delta and threatens the ranching town of Scipio. It was 64 percent contained.
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