All winter and spring, it’s been looming on mountaintops throughout the West.

Like a frozen volcano, above-average snowpack has been accumulating and threatening to overwhelm streams and rivers when the temperatures rise, and county officials have braced for what will eventually rush downhill. It’s deferred precipitation.

Throughout the West, the U.S. Department of Agriculture’s National Water and Climate Center maps show remaining snowpack in early May well above 150 percent of median snowfall for the date, backing up anecdotes that many of these communities haven’t seen snowfall like this for decades.

The Wasatch Mountains along Salt Lake County, Utah’s border flow westward into seven canyons, many of which contain entire communities of hundreds of residents, giving County Mayor Jenny Wilson roughly 600 square miles of stream front to be concerned about since the scope of the snowfall became apparent.

In mid-April, a string of days that topped 70 degrees prompted her to declare a state of emergency April 13, allowing the county to supplement its flood control and public works staffing. 

“We don’t know when the temperature hits, we don’t know if we’re going to have gradual temperature increases — that’s our best friend,” Wilson said.

“It was in the 50s last week and it will be in the 80s this week, so it will be all-hands-on-deck.”

Salt Lake County public works and flood control staff work to clear culverts and clear debris from streams, which could create blockages along streams or add hazards to flooding.

The county has asked residents to bring in firewood and other supplies that would ordinarily stay outdoors to prevent them from being washed away and added to the debris. 

Most of the sandbagging has been a volunteer effort, drawing hundreds of residents to protect their homes and neighborhoods.

“We have an incredible amount of community engagement, residents are filling sandbags, they’re helping their neighbors, our cities are all preparing locations,” Wilson said.

A $3.7 million budget adjustment has added 11 contracts for emergency management crews.

A total of 54 county staff have been rotating on 12-hour shifts for weeks, with an additional 20 during peak times.

“We’ve had public works personnel going in to give flood control a break, trying to keep the workload manageable,” Wilson said.

“Once the temperature falls again, it slows the melt and gives us a lull to regroup and get ready for the next melt.”

The eastern communities in Salt Lake County are among the most densely populated areas threatened by heavy snowmelt flooding, but many other counties are facing similar challenges.

Montezuma County, Colo. has already had its fair share of snowmelt, particularly in the city of Dolores, which suffered from flooding for a week.

“We have significant amounts of water spreading off the north side of the canyon,” said Vicki Shaffer, the county’s public information officer. “There’s a lot of National Forest service land up above that and they received a lot of snow. When it melted, it quickly overwhelmed the system of ditches and culverts.” 

When the flooding infrastructure fails, the water keeps moving where it can, washing out roads and in one small Montezuma County community’s case, deteriorating the supports for a bridge that connects residents to the rest of the county.

Like in Salt Lake County, the volunteer response has been crucial to protecting homes.

“We had hundreds of people come out to fill sandbags and then place them where they were needed, so they helped the public works people out there quite a bit,” Shaffer said. “We were very impressed with the turnout.” 

It’s been a long winter in Mono County, Calif., in the Sierra Mountains, where everything is at high altitude, getting a lot of snow.

Supervisor Bob Gardner said the county’s focus has been on keeping culverts clear and hoping warmer rain doesn’t compound the pace of melting.

“We’re trying to anticipate where the water will get backed up and make sure there’s somewhere for it to go that isn’t people’s crawl spaces,” he said. 

Highway 395 was closed for several weeks due to severe avalanches, and another community was cut off entirely. 

“All along we’ve been saying, ‘Look, we need that precipitation, so we don’t want to look this gift horse in the mouth, but we’re not used to having you know three, four, five feet in one storm,” he said.

“You can’t plan or staff for an extreme situation like this, because they’re so rare.”

Lawrence County, S.D. is on the northeastern end of the higher-than-average snow zone, and Emergency Management Director Paul Thomson said the steep slopes work to his community’s advantage when it comes to snowmelt. 

“It’s steep enough here that the water just rushes by on its way downhill,” he said.

“We don’t get inundated like they would on the eastern side of the state, where there’s about a foot’s difference with Nebraska.”

As the calendar moves deeper into May, counties are getting closer to the end, and it’s up to the weather whether it will come swiftly.  

“We’ve been working with the National Weather Service in Grand Junction and they’ve been incredibly helpful and just so we know kind of what to expect,” Shaffer said.

“This morning’s report detailed that we’re at 196 percent of the snow water equivalent still left up in the mountains for this date, so we’ve got a lot more coming.”  

Thomson said the best thing to hope for is consistency.

“I always tell people I don’t get nervous if we get a lot of snow,” he said. “I don’t get nervous if we get a lot of rain. I get nervous if we get both.”

In Salt Lake County, what is likely the last act of snowmelt season will come from Big Cottonwood Canyon and Little Cottonwood Canyon to the south.

Wilson said the snowmelt flooding will likely last through the end of June.

“We hope to be in the clear by July 4.”