THIS AVALANCHE FORECAST EXPIRED ON January 7, 2020 @ 11:33 pm
Avalanche Forecast published on January 7, 2020 @ 6:33 am
Issued by Clancy Nelson - Flathead Avalanche Center

Swan Range
Flathead Range and Glacier National Park

How to read the forecast

New and drifted snow will cause the danger to rise rapidly by this afternoon. Exercise more caution the higher up you go. Today, large avalanches can fail in the new snow and on buried weak layers. Rain and rising freezing levels may cause loose wet avalanches at lower elevations. Traveling at upper elevations is not recommended. Choosing low angle slopes and simple terrain will help keep you safe at lower elevations.

4. High

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Above 6500 ft.
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

3. Considerable

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5000-6500 ft.
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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3500-5000 ft.
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
  • 1. Low
  • 2. Moderate
  • 3. Considerable
  • 4. High
  • 5. Extreme
Avalanche Problem 1: Storm Slab
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Dense new slabs over softer, weaker snow will become larger and more sensitive as you gain elevation. Expect slabs to be larger and stiffer in exposed, leeward terrain. Very dangerous avalanche conditions are developing as more heavy snow falls and gusty southwest winds continue to blow. Avoid slopes steeper than about 30 degrees. Avoid undercutting avalanche terrain. Shooting cracks, blowing snow, and natural avalanches are red flags directing you avoid avalanche terrain. Avoid tracks and runouts of avalanche paths that extend below treeline.

Avalanche Problem 2: Persistent Slab
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Very weak layers of surface hoar and sugary facets have been buried under soft snow since New Years. Feedback on these layers has been spotty because in many places there hasn’t been much of a slab over above them. That’s changing as dense storm snow and wind drifts overload these fragile layers. Crusts below will act as sliding surfaces. Whumpfing noises and shooting cracks are like alarm bells telling you to stick to lower angled, simple terrain. Smaller storm slab avalanches may suddenly overload buried weak layers, resulting in larger, dangerous slides.

Avalanche Problem 3: Loose Wet
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Rising freezing levels and rain at lower elevations will saturate the surface snow and may cause loose wet avalanches in steep terrain. Watch for rollerballs and wet snow as signs of instability. Wet sluffs will be most dangerous where there was already snow cover and where 10 inches or more of new snow gets wet. Terrain traps like gullies, cliffs, and trees will amplify the consequences of even small wet sluffs.

Forecast discussion

Another strong, warm, windy storm is impacting our area. As of early this morning, weather stations are reporting between 0.7” of new water at Flattop Mountain and 1.7” SWE at Noisy Basin. By this afternoon, those amounts could almost double. If the wind forecast verifies in higher terrain, new storm slabs could be very large. Temperatures and freezing levels are expected to rise, causing up-side-down, top-heavy snow, above 5,000 feet, with rain below that elevation.

The dense storm snow is falling on lighter, softer old snow, polished wind board, or bare, wind-scoured ground. Since Jan. 1st, observations from across the forecast area have described buried weak layers of surface hoar and sugary faceted snow sandwiched between crusts (example 1, example 2). Natural and triggered avalanches failed on these layers after the New Year’s storm, and this storm is rapidly loading them again. 

Below the snow line, triggered and natural wet snow avalanches are possible on steep slopes that had continuous snow cover before this storm. 

We have had no reports of avalanche activity on early season weak layers at the base of the snowpack since December 20th. But there have been few opportunities to view or access the terrain where those layers are most prominent. That creates uncertainty over how well they have adjusted to new loading. Treat very big alpine terrain with uneven snow cover with a healthy dose of skepticism.

Weather and CURRENT CONDITIONS
weather summary

Subtropical moisture streams across the region today with gusty ridgetop winds and rising freezing levels. Several inches to a foot plus of new snow is expected by this evening with freezing rain down low. A weak cold front will drop snow levels and create even stronger winds late tonight.

Two-Day Mountain Weather Forecast Produced in partnership with the Missoula NWS
For 5000 ft. to 7000 ft.
Tuesday Tuesday Night Wednesday
Cloud Cover: Overcast Mostly Cloudy Overcast
Temperatures: 26 to 32 deg. F. 20 to 25 deg. F. 24 to 30 deg. F.
Wind Direction: Southwest Southwest Southwest
Wind Speed: 10 to 15 gusting to 25 15 to 20 gusting to 40 15 to 20 gusting to 35
Snowfall: 10" to 12" in. 3" to 4" in. 6" to 10" in.
Snow Line: 4000' 4000' 3000'
Disclaimer

This forecast applies only to backcountry areas outside established ski area boundaries. The forecast describes general avalanche conditions and local variations always occur. This forecast expires at midnight on the posted day unless otherwise noted. The information in this forecast is provided by the USDA Forest Service who is solely responsible for its content.