How dry is it?

• Some areas of southwest Utah have gone 72 days without more than a trace of precipitation.

• Measurements of soil moisture show vast tracts of Utah are below the permanent wilting point. That means plants in those areas will die no matter how much rain eventually falls.

• Just a spark — from ammunition, fireworks or a dragging muffler — can start a fire that causes trees to explode.

"It is as bad as it can possibly be," said Randy Julander, snow survey supervisor for the Natural Resources Conservation Service (NRCS). "You can't get any worse than this."

Utah is experiencing a perfect storm when it comes to heat, wind, a lack of moisture and a wealth of dry vegetation that becomes perfect fuel for wildfires. Part of the problem is that not much has burned in the past couple of years.

"The fuels are the driest they've been in about 20 years," said Monica Traphagan, a forecaster for the National Weather Service. "We had this dry winter where we didn't have that snowpack to keep things moist. That, combined with the fact that the year before and the year before that we haven't had a lot of wildfires, means a lot of those fuels are just hanging around."

Salt Lake City is going on 30 days with no measurable precipitation. The last day a trace of rain fell in Utah's capital was May 27. But that's nowhere near a record, according to Traphagan: In 1952, no rain fell between Sept. 12 and Nov. 12 — 62 days.

But there's no rain expected in the next 10 days.

Julander said NRCS soil sensors show large areas south of Highway 6, which runs through Spanish Fork Canyon, are beyond the permanent wilting point. "Grasses and other kinds of short-rooted vegetation, most of them are dead now and have been dead for a month or more."

Trees have deeper roots, but prolonged periods without moisture can place them at risk for disease and insect damage, he said.

Many cities throughout Utah have enacted fireworks restrictions, and Gov. Gary Herbert has banned fireworks from any public land outside incorporated areas. But such rules only work if people follow them.

Randy Wilden, chief of the North Tooele Volunteer Fire Department, said the combination of low moisture and abundant fuel is already creating havoc.

"We were up chasing fireworks last night. It's already started," he said Wednesday during a meeting of the Tooele Local Emergency Planning Committee. "We had trees exploding."

Fire department Sgt. Harry Shinton explained that the sap in some trees, particularly cedars, can get so hot that they will spontaneously ignite near a fire.

"There is more moisture in a two-by-four you buy down there at Home Depot than in a tree up there," Shinton said of conditions in Tooele Valley.

Tribune staffer Kirsten Moulton contributed to this story