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Spring Flooding Ramps Up With More Rain For Montana, Wyoming, Idaho, Washington

By Jon Erdman
Published: March 9, 2014
  

This week, on the heels of another swipe of snow for the snow-weary, we've seen record-smashing cold in parts of the Midwest, South and East.

(MORE: Snowiest Cities | March Cold Records | Great Lakes Ice Nearing a Record)

With apologies to those of you who are sick of winter, I would submit Missoula, Mont. has had it toughest over the past week or so. 

Let's recap what they've gone through:

That's more snow in one month than their annual average of 39.9 inches! The 30-year average February snowfall, typically only the third snowiest month in Missoula, is 6.5 inches. According to the National Weather Service forecast office in Missoula, 26 of 28 February days featured at least a trace of snow.

This was punctuated by a snowstorm at the end of February into March during which 11.9 inches of snow fell.

Not only was travel snarled, but the combination of high winds and heavy snow created an unstable snow slab on Mt. Jumbo northeast of downtown Missoula, eventually releasing a deadly avalanche on Feb. 28 in Rattlesnake Valley.

(MORE: Avalanche Buries Montana Home)

According to an article in The Missoulian, the avalanche released an estimated 80 percent of the snow in the Mt. Jumbo basin. It was the first slide on the west face of the mountain in at least 50 years.

Then, on Tuesday, a plane slid off a runway into a snowbank at the Missoula International Airport while taxing. No injuries were reported among the 44 passengers and three crew members.

Now, it's rain and warmer temperatures that are a concern.

Flood Threat

Worland, Wyo. ice jam flooding

An ice jam triggered flooding in parts of Worland, Wyo. on Mar. 7, 2014. (Photo: WyoDOT via NWS-Riverton, Wyo.)

While the Arctic air has retreated, the Pacific storm track remains pointed at the Northwest and northern Rockies, as it typically is in late winter.

For most valley locations, this means a break from the snow. However, this isn't the rosy picture it may sound like. There are three main impacts from this warmer pattern change: 

  • Flooding in low-lying areas, as rain, coupled with warmer temperatures, melt the existing snowpack.
  • High avalanche threat due to heavy wet snow, even rain, loading on existing snowpack in the mountains.
  • Refreezing of meltwater overnight will lead to icy stretches on roads, driveways, and sidewalks during the morning.

Friday, an ice jam on the Big Horn River lead to flooding of some residential areas of Worland, Wyo.

Thursday, one waterproofing contractor in Missoula, Mont. fielded at least 50 calls from residents with flooded basements, according to a story in The Missoulian. Sandbags are now being made available to residents in Missoula, and other parts of the Big Sky State.

Standing water covered a stretch of Interstate 90 near Bozeman, Mont. on Thursday.

Background

Pacific Satellite Image

Pacific Satellite Image

Pacific Satellite Image

Pacific Satellite Image
Background

Rainfall Forecast

Rainfall Forecast

Rainfall Forecast

Rainfall Forecast

Flood alerts are posted from parts of Washington state to the northern High Plains. 

Another round of valley rain and high mountain snow is headed for the Northwest and northern Rockies this weekend.

In the flood-affected northern Rockies, the precipitation will continue on Sunday, with snow levels dropping by Monday into Tuesday before moving out later Tuesday.

(MAPS: Sunday | Monday | Tuesday)

How much more rain will fall in valley and foothill locations below snow level? 

  • Western/southern Mont., northern/central Idaho, far eastern Wash., northeast Ore.: Up to another inch possible, with local one-inch-plus in northeast Ore., Idaho.
  • Western Wash., western Ore.: 1-2 inches, with locally higher amounts on windward slopes of the Cascades and Olympics.
  • Northwest California: 2-3 inches, locally higher in coastal ranges; possibly up to an inch of rain in the northern Sierra foothills.

(FORECASTS: Missoula | Bozeman | Spokane | Seattle)

Expect rapid rises on small creeks and streams in the Northwest during periods of rain through Sunday. 

Once snow levels drop, over a foot of snow is possible by later Tuesday in some parts of the Bitterroots and Tetons.

The danger of avalanches will remain elevated. Avoid backcountry and out-of-bounds areas until the danger subsides.

MORE: Wilderness Career: Avalanche Forecaster

An avalanche dog frees a person buried in the snow, on December 11, 2012, during an avalanche dogs training session near Les Deux Alpes ski resort in the French Alps. (JEAN-PIERRE CLATOT/AFP/Getty Images)


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