Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

At least a foot of new snow in the Bitterroot will continue to raise the avalanche hazard. New snow totals across the Bitterroot range from less than a foot to upwards of two feet, with the central Bitterroot receiving the most snow so far. 

Storm slab exists on all aspects at mid and upper elevations, especially in areas where the wind has built fresh wind slab. Wet loose avalanches are possible at low elevations below the rain/snow line. 

Travel in avalanche terrain is not recommended today. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Overnight, at least another foot of snow fell in the Bitterroot. Storm totals vary across the range, with the central Bitterroot receiving the most water so far. Snow totals at upper elevation are unknown right now but judging by the amount of water, storm totals are likely up to 3 feet. In the southern Bitterroot, the storm was at 9 inches yesterday, bringing the total up to 2 feet for the storm. In the northern Bitterroot around Lolo Pass and Skookum lake, there was a foot of snow yesterday, with the storm total now about 2 feet. 

    There is a density inversion within the storm snow, with reports of high density snow falling yesterday on top of lower density snow from the start of the storm. Today, snow will return to low density as colder air arrives. There is also a thin crust midway through the storm snow that formed during a period of warmer temperatures and freezing rain on Sunday. 

    Yesterday, observers in the southern Bitterroot were able to trigger small soft slabs within the new snow with ski cuts and by dropping cornices. No large avalanches were observed, but visibility was poor into adjacent terrain. 

    Ridgetop winds for the past 24 hours have been steady from the west. In the southern Bitterroot, observers noted strong west winds throughout the day.  In the northern Bitterroot, winds started light yesterday before increasing to strong by mid afternoon. Previously, reports had come in of wind transport and loading onto mid and upper elevation north through southeast terrain. Expect wind slabs on east aspects and complex terrain cross loaded by strong winds. 

    Considerable hazard is a large spectrum. In fact, it is the largest spectrum of all the avalanche hazard ratings. We are at the upper end of considerable today in the Bitterroot. Some areas may reach high hazard. Today is not the day to be in avalanche terrain.

    Avoid slopes steeper than 30 degrees, convex rollovers, and terrain traps. Wind slab can be identified by its smooth rounded appearance. If you experience cracking or collapsing, stay on low angle terrain. Stay back from the edge of cornices as they can break back further than expected. 

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Temperatures have remained above freezing at lower elevations for the past 36-48 hours. At 6500’ in the central Bitterroot, temperatures did not reach freezing until 3am this morning. The elevation of the rain line is uncertain right now, but wet snow avalanches are possible anywhere rain is falling on fresh snow.

    If you find yourself in the rain today, expect wet snow avalanches. Stay off of slopes over 30 degrees, and be aware of what terrain is above you.

Avalanche Discussion

After a few weeks of relatively benign weather, a strong winter storm has been impacting the area since Saturday. Snow totals are impressive, especially around Seeley Lake with up to 5 feet of snow. South, in the Bitterroot, snow totals are significantly less but still 2-3 feet. 

Dangerous avalanche conditions exist in the mountains today. A density inversion in the storm snow brings the potential for storm slab avalanches. This forms when the storm starts cold, as it did Saturday with low density falling. Sunday, temperatures warmed, and snow densities increased. The dense snow forms a slab, with the low density snow below acting as the weak layer. These avalanches can be very sensitive and break slopes down to 30 degrees. The good news is that instability from storm slabs, especially from density inversions, is usually short lived and only lasts a few days. Give the storm snow time to settle and bond. Don’t get sucked into a powder panic today. 

We have been without our Point 6 weather station above Snowbowl for 24 hours now, likely due to a rime event. This complicates the understanding of overnight winds in the northern half of the forecast zone. Between field observations from yesterday and models of overnight winds, I have high confidence that winds continued to blow out of the west overnight. That being said, be suspect of all aspects for wind loading along ridgelines. 

During storms like this with degrees of spatial uncertainty, your observations help a lot! Even something as simple as letting us know how many inches of snow fell where you skied helps us fill in the gaps in the forecast area. A picture or video is even better! Please consider taking the time to submit an observation if you are in the mountains today. 

Ski and ride safe. 

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