Freezing Thawing

A truck drives through a large puddle of standing water on Missoula's Northside on Thursday. Warming temperatures are causing snowmelt to pool in areas that can't drain, and frozen water lines could continue to be an issue for another week.

The extended 2019 winter cold has produced a rare freezing effect on some underground water pipes in the Missoula area.

A handful of homes have reported frozen water lines due to unusually deep ground frost, according to Missoula Deputy Public Works Director Dennis Bowman. The problem is much more serious east of the Continental Divide, where hundreds of homes in Helena and Great Falls may be affected.

“The frost is getting down 5 to 6 feet deep in some places,” Bowman said on Thursday. “It’s been on the South Side and up in the Rattlesnake neighborhood and parts of East Missoula where it’s shaded. We felt it was better off to let everybody know.”

From Feb. 1 to March 12, the average temperature in Missoula was 16.8 degrees, according to National Weather Service records. That’s cold enough to freeze the soil to depths close to underground water lines, causing them to break. In counterintuitive fashion, melting surface snow can aggravate the problem. Snow actually insulates the soil. So uncovered ground, like cleared driveways or plowed streets, allows nighttime cold to penetrate deeper into the ground, occasionally reaching water lines.

A solution exists. Leaving a faucet running at a slow trickle will draw above-freezing water through the underground pipes, keeping them just warm enough to avoid ice formation.

“You might have to do it for another week,” Bowman said. “But it’s a lot cheaper to run the water for two weeks versus digging up the ground which will cost $5,000 to $10,000.”

Helena residents endured several days of minus-40 temperatures during the worst of the March winter cold. That’s pushed the frost line deep enough to break 3-inch service lines buried 5 feet deep.

Missoula-area weather has shifted toward spring conditions, with highs forecast in the upper 30s for Friday and the mid-50s by next Tuesday. However, nighttime lows will remain in the teens to upper 20s through at least Monday.

That may lead to snowmelt issues such as standing water on roads and lawns, potential for leakage into basements and outdoor buildings, and clogged drainage systems.

The National Weather Service has issued a hydrologic outlook for all of western Montana, warning that melting snow may not be absorbed by the still-frozen ground. While the agency has not issued the more serious flood advisory for the Missoula area, its outlook does warn of the potential for “lowland flooding, water on roadways and basement flooding.” It also suggests careful monitoring of creeks and streams for potential ice jams that can push water out of channels.

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Natural Resources & Environment Reporter

Natural Resources Reporter for The Missoulian.