Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 16th, 2020–Dec 17th, 2020

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

Regions

South Rockies.

Wind slabs are likely reaching threshold and could be reactive to human triggers. Choose conservative terrain and watch for signs of instability such as whumphing, cracking and recent avalanches.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Wednesday Night: Snow amounts 5-10 cm with ridgetop wind strong from the southwest. Freezing levels valley bottom. Ridgetop winds 40-70 Km/hr from the southwest.

Thursday: Cloudy with some sunny periods. Snow amounts generally light through the day. Ridgetop wind 45-85Km/hr. from the southwest.

Friday: Light amounts developing through the day and overnight. Ridgetop wind 55-85Km/hr from the southwest.

Saturday: Snow through the day near 10 cm with rising freezing levels to 1600 m. Winds continue to blow 35-95Km/hr.

Avalanche Summary

No new avalanches to report on Wednesday, but visibility was poor due to clouds and blowing snow.

Wind slabs may be reactive on Thursday at treeline and above.

Please consider sharing your observations on the Mountain Information Network. Thank you to those that have already submitted this winter.

Snowpack Summary

10- 20 cm of new snow and strong to extreme ridgetop wind from the southwest is forecast for the rest of the week along with a bit of new snow. New and reactive wind slabs will likely build at treeline and in the alpine.

Currently, 30-50 cm of snow from last week overlies a hard melt-freeze crust formed in early December at least up to 2000 m. To date, this layer has not been an avalanche concern but by Thursday it may reach its tipping point and that concern and hazard will likely increase with snow/wind load and rising freezing levels. Use caution if you find cohesive snow above the crust, particularly if there are weak, sugary faceted grains immediately above or below the crust. 

The snowpack depth varies substantially in the region and has been described as thin, wind-hammered, variable, and tapering rapidly at lower elevations. The average snowpack depth at treeline is approximately 100 cm.

The middle of the snowpack has been reported as being well-consolidated and may host another hard melt-freeze crust.

The base of the snowpack consists of a hard melt-freeze crust from early-November that may have faceted grains around it. There has not been recent avalanche activity on this layer but it remains on our radar. The most likely spot to trigger it would be on thin and rocky slopes.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • 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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.