Wet Slabs
N
NE
E
SE
S
SW
W
NW
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2
There will certainly be some wet loose avalanches, but the greater threat are wet slabs that may occur as buried persistent weak layers become wet.
Avalanche forecast
View on mapCooke City
Gallatin NF Avalanche Center
Avalanche danger
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
Out of date — this forecast expired 5 months ago. You’re viewing past conditions, not the current bulletin.
Highlights
Record heat is causing rapid changes in the snowpack with multiple overlapping avalanche problems making dangerous avalanche conditions. The best travel advice is to avoid avalanche terrain today and the next few days until the snowpack can cool off and refreeze.
Avalanche problems
Persistent Slabs
NNEESESSWWNW- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2.5
Some were remotely triggered just a few days ago like this one
Cornices
NNEESESSWWNW- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 1–2
Falling cornices trigger avalanches on the slopes below. They also break further back than you'd expect.
Avalanche Discussion
The snowpack is changing rapidly causing a lot of uncertainty with exactly how likely avalanches are today and how they will behave; however, there are a few things we do know for sure:
- There are widespread persistent weak layers buried 1-3 ft deep. Some are facets from the long dry period in January. Others are facets and/or surface hoar that formed in mid February.
- Liquid water on many slopes, especially on southerly facing ones, is starting to move down through the snowpack - a bad thing for stability.
- Last night, air temperatures remained above freezing everywhere which means the snowpack is starting off pretty warm and will become wet quickly today.
- Today should have record breaking temperatures with plenty of strong sunshine.
Yesterday there were two notable avalanches observed on Cedar Mountain near Big Sky triggered by falling rocks and cornice chunks (first one, second one). It’s hard to say if those slides were wet slabs or persistent slabs or some hybrid mix of the two, but the heat certainly caused the falling rocks and cornice chunks. I suspect there were at least a few other similar avalanches yesterday but no one saw them.
Prior to this heatwave, there were plenty of both wind slab and persistent slab avalanches. View avalanches in the past week HERE
What does this all mean? Liquid water percolating through the snowpack, possibly weakening buried layers of facets and surface hoar, can cause wet slab avalanches. Additionally the heat will cause cornices to break. Falling cornices make great triggers for avalanches. Avalanche activity often spikes during intense snow storms; consider our current weather to be an intense solar/heat storm which can also cause a spike in avalanche activity.
What to do today?
- Let the snowpack go through this transitional phase and don’t trust it. It’ll be grumpy, so give it space until it cools down (just like people).
- Avoid being under steep slopes that have overhanging cornices that may fall and trigger avalanches.
- If traveling on ridgetops, stay far away from the edge as cornices can break unpredictably and often break further back than you think.
There are likely some higher elevation, north facing slopes that harbor dry snow and good riding, BUT they also harbor persistent weak layers buried 1-3 feet deep. Even if the snow is dry and cool, I wouldn’t trust those weak layers due to the weirdness from this record heat.
Conditions today are dangerous and the avalanche danger is CONSIDERABLE with the possibility of wet slabs, persistent slabs, and falling cornices. Wet loose avalanches are much more likely on slopes where the snow is getting wet, but wet slab avalanches on those same slopes will be the much more dangerous problem.