Spring storm boosts Wyoming flooding threat

2011-05-18T23:45:00Z 2011-05-18T23:55:06Z Spring storm boosts Wyoming flooding threatThe Associated Press The Associated Press
May 18, 2011 11:45 pm  • 

CASPER, Wyo. — It’s late May, but snow keeps falling in the Rockies, adding to record snowpack that could mean major flooding come spring melt.

“These are historic levels of snow,” said Don Day, meteorologist with Cheyenne-based Day Weather Inc. “It’s amazing, and we’re just adding to it, not getting rid of it.”

A strong spring storm system was expected to bring up to 2 feet of fresh snow by the end of this week to Wyoming’s mountains, along with up to 3 inches of rainfall at lower elevations. All of the state is in line to receive snow and rain through at least Friday morning, forecasters say.

Coming on top of snowpacks that already exceed 200 percent of average in some areas, and saturating soils at lower elevations, the latest storm appears to be setting the stage for a wild and woolly June along Wyoming’s rivers and streams.

“At this point, everybody is just sitting back chewing fingernails and waiting because the longer it stays cold and wet, the worse it’s going to get,” said Randy Julander, a supervisor with the U.S. Department of Agriculture’s Natural Resources Conservation Service.

In southwestern Carbon County, the swollen Little Snake River has already begun flooding low-lying areas upstream and downstream from the town of Baggs, Mayor Kathy Staman said Wednesday.

On Mother’s Day, town residents began reinforcing levees in preparation for high water. Locals have also laid sandbags to protect homes and businesses.

It rained in Baggs on Wednesday morning, and the town was expecting snow to fall in the surrounding mountains overnight. Residents are concerned, Staman said.

“A lot of them had gone through the flood of ’84, which totally flooded the town,” she said. “So they know how much water has to come down the river. ”

‘Delaying the inevitable’

Major flooding in Wyoming generally occurs with a combination of high snowpack, rapidly warming temperatures and rain. The good news with the current storm system, Day said, is that below-average temperatures haven’t unleashed high-elevation snowmelt.

“With big rain like this coming in, if it were after three or four days of highs in the 70s and 80s, things would be really wild,” he said. “It’ll still be touch and go, but not like it could be.”

The bad news, though, is that all the moisture is still sitting in the mountains, waiting for warmer temperatures to send it downstream.

Julander said in a typical year the weather warms gradually, allowing snow in the mountains to melt slowly and ease into rivers and streams over time. That’s not the case this year.

“June is right around the corner and sooner or later, it’s going to warm up,” he said, noting that instead of gradually warming over eight to 10 weeks, the West will likely see a rapid rise in temperatures heading into summer, a worst-case scenario.

“It’s been so cold that it’s not melting out. It’s just delaying the inevitable,” Day said. After observing southern Wyoming mountains from the air last weekend, he said the high-elevation snow fields look like they generally would in February or March, rather than May.

Snowpack numbers from the Natural Resources Conservation Service confirm Day’s observation. As of Wednesday morning, before the latest storm hit, water content in snow in the Upper North Platte Basin stood at 200 percent of the historical average. Other areas with big numbers included the Snake River Basin, 195 percent; Powder-Tongue river basin, 194 percent; the Little Snake River Basin, 204 percent; the Upper Green River Basin, 203 percent; and the Upper Bear River Basin, 267 percent.

“I’ve never seen it that high,” Day said, while cautioning that some snowpack numbers are beginning to be skewed because there’s still snow at some low-elevation measuring stations that usually don’t have any at this time of year.

Soggy situation

Jim Fahey of the National Weather Service in Riverton said the current storm system isn’t expected to cause anything more than minor flooding in parts of southern Wyoming immediately. But it’s still going to be wet.

The cold low-pressure system from the Northwest, drawing moisture from the Pacific and Gulf of Mexico, began hitting the state Wednesday and was expected to linger through Friday morning. While rain was falling at lower elevations, snow was expected to accumulate at elevations above 6,500 feet — up to 14 inches in the Absaroka and Owl Creek mountains, 2 feet in the northern Big Horns, 12 inches in the Wind Rivers and Rattlesnake Range, and 18 inches in southern Wyoming mountains.

Colorado and Utah mountains also were seeing significant snowfall, and officials said mudslides, avalanches and flooding could become major issues in the coming days.

As for when the runoff will begin in earnest, forecasters say it’s not imminent. Daytime temperatures are expected to be in the low to mid 60s well into next week, and Day said more springlike storm systems are possible.

In Baggs, Mayor Staman said that while there’s been no flooding in town yet, residents know the worst is still ahead.

“We are in good shape right now,” she said. “But there is a lot of water content in the mountains, and we are probably not going to be out of the woods for another two weeks.”

Day was less optimistic, saying he expects high water in Wyoming’s rivers and streams “the whole month of June.”

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