Bitterroot

Human triggered avalanches will be likely today in wind loaded terrain. Larger avalanches 3-5 feet deep are possible in areas with buried surface hoar or weak snow around crusts. Smaller avalanches have the potential to step down and trigger larger or more destructive avalanches. 

You may not see any red flags like collapsing or cracking before triggering a larger persistent slab avalanche.

If you want to avoid avalanches today, stick to slopes less than 30 degrees in slope angle and be aware of what avalanche terrain is above you at all times.

Considerable danger, like all avalanche danger ratings, are a spectrum. The central and southern Bitterroot are in the middle of the considerable rating, where the northern Bitterroot and Rattlesnake are on the lower end.

Yesterday, multiple people were buried in avalanches in Utah with one fatality. Condolences to their friends and family.

The snowpack is trending in a good direction, but we still have a 1 meter slab on top of a known weak layer. Observations have shown intermittent propagation in tests, but don’t let that fool you into thinking there is no danger. Enough SWE (snow water equivalent) is above the weak layers to produce dangerous D3 avalanches. So are we in “low probability/ high consequence” conditions? Not quite. Buried surface hoar is never a low probability problem. Be suspect that any non solar slope is holding buried surface hoar and dig in multiple areas to look. It will present as a thin grey line across the pit wall. 

We are in a period of complex avalanche conditions with a lot of uncertainty. The more complex and overlapping the problems are, the more it pays to keep your decision making simple. If you try to outsmart the overlapping problems, you are asking for trouble. 

How did we get here? Since the beginning of month, a series of storms has hit the forecast area putting down between 2-5 feet of snow, with the higher totals found in the central Bitterroot and along the Bitterroot crest. This new snow greatly improved skiing and riding, but is not without problems. Ahead of the storm a long period of high pressure with no new snow and cold temperatures formed an overlapping assortment of weak layers at the snow's surface that are now buried by the new snow. New snow following a prolonged period of cold high pressure is a well known avalanche danger pattern. 

The distribution of the weak layers across the mountains still has some uncertainty. Prime surface hoar growth weather was present from the 19th of January through the 27th. In addition to surface hoar, all aspects formed near surface facets at the surface. On the 28th and 29th, temperatures warmed into the low 40s with strong sun on solar aspects, forming a melt-freeze crust on top of the near surface facets, while destroying the surface hoar on solar facing slopes. 

Then we began to see snow on February 1st with light winds as the storm arrived. Since then, it's kept snowing and the SWE (snow water equivalent) totals are upwards of 3 inches of water. The new snow has been low density, but is slowly forming a more cohesive slab. On February 3, an Avalanche Warning was issued for warming temperatures and high precipitation rates with potential for this to tip us into a natural cycle. Since then, we have had a few more days of steady but light snowfall and shifting winds. 

Please continue to submit observations and help us keep an eye on changing conditions. Check out this video on what makes a useful observation. 

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Ski and ride safe.