Avalanche forecast

Banner Summit

Sawtooth Avalanche Center
View on map

Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You are most likely to trigger a 1-3 foot thick avalanche on slopes where the wind has formed drifts or stiffened the snow at or near the surface. Large avalanches are also possible in terrain sheltered from the wind. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. 

The avalanche danger will increase dramatically after dark and is likely to reach HIGH by tomorrow morning. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    You could trigger 1-3 foot thick avalanches on buried weak layers (sugary facets or crust + facet combinations). The steady stream of snowfall and windblown snow has many slopes teetering on the edge, just waiting for a trigger.

    The distribution, character, and sensitivity of the weak layers vary from slope to slope. Your best bet is to assume this problem exists and choose terrain accordingly. Conditions are most dangerous where wind slabs and drifts have formed a thicker, more cohesive slab. However, the snowfall from the past couple of weeks has become cohesive enough to act as a slab on most sheltered slopes.

    You can reduce your risk by avoiding slopes steeper than 30 degrees—especially large avalanche paths and those with ugly consequences if you are caught in a slide. Persistent weak layers can fail unpredictably and break significantly wider, deeper, and higher on slopes than you might expect, producing much larger avalanches. You could remotely trigger avalanches from gentle terrain above, below, or to the sides of steep slopes. Avalanches could be triggered by the second, third, or fourth rider on a slope.

    ADDITIONAL DISCUSSION: Small amounts of snow and light to moderate SW-S-SE wind over the past 36 hrs may have combined to build fresh, thin, sensitive wind slabs. Look for them near ridgelines and mid-slope terrain features like ribs and gullies. Small wind slabs can make effective triggers for the larger persistent slab avalanches described above.

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain (great skiing and riding conditions) is an excellent example of a slope that did not need wind loading to become unstable. 

Avalanche Discussion

Concerning the weather, today is the "lull before the storm." As far as avalanche conditions go, however, we're experiencing one of the riskiest weeks of the season. A weak snowpack, loads of inviting powder, and Spring-like sunshine are a dangerous mix. Avalanche conditions remain dangerous across the majority of the Forecast Area. Recent signs of instability are numerous and easy to find:

  • Skiers and riders triggered many large avalanches in recent days (list).
  • Several of the slides were triggered remotely, from gentler terrain above, below, or to the sides of steeper slopes.
  • Some of the avalanche crowns formed higher than usual, where the slope looks too flat to avalanche (photo).
  • Yesterday, Ben experienced several booming snowpack collapses throughout his tour east of the Wood River Valley, and observed an additional 7-8 recent large avalanches. Similar snowpack collapsing was reported from the north side of Galena Pass. 

Two trends in recent avalanche activity are apparent:

  1. Conditions become more dangerous as you move south of Banner Summit and the Stanley area (see "Avalanches by Zone" graphic below). 
  2. Triggering avalanches has been most likely on NW-N-NE-E-SE aspects (see "Avalanches by Aspect and Elevation" graphic below). While we have not seen large avalanches release on W-SW-S aspects in the past week, the snowpack structure is concerning on many of those slopes.  

Continue to treat the ugly snowpack structure with respect; don't let powder lull you into complacency. Build in a larger-than-normal safety margin, and expect to be surprised. Thankfully the unusually fluffy powder allows us to have fun on low angle and flat terrain.

Regions covered