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'Mountain wave' rips into Missoula, topples trees

'Mountain wave' rips into Missoula, topples trees

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A wind storm toppled trees Wednesday, slowing traffic and causing power outages throughout Missoula and across the state.

A National Weather Service sensor recorded gusts of 125 mph on Mount Sentinel. NorthWestern Energy crews expected to have power restored to everyone in Missoula and Hamilton by midnight Thursday, said Jo Dee Black, a public relations specialist for NorthWestern Energy.

Marie Anderson is an Urban Forestry Specialist with Missoula Parks and Recreation and was monitoring trees being buffeted by the winds in the University District. The ground isn't frozen right now, but is extremely wet, Anderson said. Because of this, many trees with shallow root systems were at risk of falling.

One tree fell behind the Unitarian Universalist Fellowship, 102 McLeod Ave., crushing the church's back fence and causing the house across the alley to lose power. Alice Barts, 6, saw it happen. 

"I was right in the middle of a meeting," Barts said. "And I was pretty stressed out and then I saw the tree fall."

Bailey Marvin's car was flattened by a tree outside his house on the corner of Livingston Street and Lester Street. Marvin said he saw the power go out and went outside to see what was happening.

The huge evergreen in the front yard fell right before his eyes, making a loud sound as the underground roots snapped. It took out a power pole on the way down before it landed squarely across his car. Marvin said the only good thing was the tree fell toward the street, and not on the house he had just finished renovating.

In the University District, city officials closed off Gerald Avenue between Keith Avenue and McLeod Avenue after a tree fell outside the University of Montana president's house. 

Bob Smith, director of Facilities Services at the university, said another tree on the property needed to be taken down as well due to the severe winds.

One tree fell across South Higgins Avenue near the McLeod Avenue intersection, which slowed traffic for several hours. The tree tangled in some power lines and the Missoula Fire Department had to wait for NorthWestern Energy to shut off power before they could move the tree.

NorthWestern Energy was overrun with calls about outages, low-hanging branches and downed power lines, Black said. The company turned off its outage map briefly on Wednesday due to the number of outages being reported across the state, Black said. 

"At some point there are just so many individual outages across the state, it becomes impossible to read," Black said. 

While it will take a few days to quantify how many outages took place on Wednesday, Black said it was unusual to have weather hitting so much of NorthWestern's service area at the same time. Blackouts stretched from eastern to western Montana.

A rare weather phenomena called a mountain wave helped cause the damage across Missoula, according to NWS meteorologist Alex Lukinbeal.

“It’s like in a stream, where you see water flowing over a rock to create a rapid — wind accelerates like that down a mountain crest,” Lukinbeal said. “What probably happened on Sentinel, is the wind accelerated coming down the mountain crest to the west, and slammed into the face of Sentinel. Thankfully it didn’t make it down the valley floor, or it would have done a lot more damage.”

Mountain waves differ from microbursts or straight-line waves, which have also toppled trees in the Missoula Valley. Those winds typically form as side effects of thunderstorms in warmer conditions.

On Tuesday, NWS meteorologists warned that 1 to 3 inches of rain could be soaking the Montana-Idaho border region. That would be followed by strong downslope winds lasting from 5 a.m. to 11 a.m., followed by gusty conditions across west-central and southwest Montana through Wednesday afternoon. Gusts of greater than 50 mph were expected. 

They showed up just slightly after predicted, with Missoula feeling the brunt around noon Wednesday.

However, the winds were expected to drop by Wednesday evening as the system was to move to the east.

Conditions are different in the mountains across western Montana. The Flathead Avalanche Center in Hungry Horse issued Backcountry Avalanche Watch alerts on Wednesday for the Swan, Whitefish and Flathead mountain ranges and Glacier National Park. Observers reported the new and extremely wet snow combined with high winds was overloading many slopes on top of very weak layers, resulting in long-running slides at lower-than-usual elevations.

Consult or for more detailed information.

Missoulian reporters Ashley Nerbovig, Tom Bauer, Ben Allan Smith and Rob Chaney contributed to this story.


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