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Avalanche Forecast

Archived

Dec 13th, 2020–Dec 14th, 2020

Alpine
Natural avalanches unlikely.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies.

Small wind slabs may remain reactive to human triggers in isolated locations. Use caution when transitioning into wind affected terrain.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

  

SUNDAY NIGHT: Cloudy / Moderate, northwest ridgetop wind / alpine low temperature -15 / Freezing level valley bottom.

MONDAY: Cloudy / Light, northwest ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.

TUESDAY: Snow; 3-5 cm. / Strong, southwest ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.

WEDNESDAY: Cloudy with isolated flurries; 0-3 cm. / Strong, west ridgetop wind / alpine high temperature -6 / Freezing level valley bottom.

Avalanche Summary

No new avalanches were reported in this region on Saturday.

Data in this region is very sparse. Please submit your observations to the Mountain Information Network. 

Snowpack Summary

Strong northerly winds formed wind slabs on lee features at treeline and above. 

10- 20 cm of recent snow fell at upper elevations while the rest of the precipitation came in as rain or freezing rain. Recent reports suggest that the freezing rain occurred from 1800m to 2000m “ish” with rain at lower elevations which may have destroyed the surface hoar at 2000m and below. All elevations are now hosting a burley crust under the new snow. Up high, stiff wind slab exists on leeward slopes where the new snow deposits into deeper drifts, especially where the new snow sits above this recent rain/freezing rain crust, or the older melt-freeze crust found on solar aspects.

Digging deeper in the snowpack two crusts exist from November. One down approximately 30 cm, just below the old surface hoar, and the other sits deeper (down 70-90 cm) and is widespread up to 2500 m. The deeper crust seems to be bridged by a well-consolidated mid-pack in most areas. These crusts have shown no recent reactivity in snowpack testing but remain on our radar moving forward.

The snowpack is generally thin, wind hammered, variable in wind-scoured areas, and tapers rapidly at lower elevations. Snowpack depths at sheltered upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid areas where the snow feels stiff and/or slabby.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.