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

Feb 4th, 2021–Feb 5th, 2021

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

Regions

Purcells.

Human triggering of LARGE avalanches continues to be LIKELY on Friday. The persistent weak layer of surface hoar will be slow to gain strength and requires continued conservative terrain choices.

Confidence

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

Weather Forecast

  

THURSDAY NIGHT: Cloudy with isolated flurries; 0-3 cm. / Light, northwest ridgetop wind / alpine low temperature -14 / Freezing level valley bottom.

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

SATURDAY: Cloudy with flurries; 0-3 cm. / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.

SUNDAY: Cloudy with isolated flurries; 0-3 cm. / Moderate, northwest ridgetop wind / alpine high temperature -12 / Freezing level valley bottom.

Avalanche Summary

On Tuesday, several skier triggered storm slabs up to size 2 and numerous explosive triggered storm slabs up to size 3 were reported near Golden. 

Most notable was a report of skier remotely triggering a size 2.5 storm slab from a ridgetop at treeline near Quartz Creek. This avalanche failed on the very weak layer of surface below the recent storm snow. It was reported that light wind effect had stiffened the recent storm snow just enough to be highly reactive to skier triggering. Min report HERE.

Touchy storm slabs are sitting on a weak layer of surface hoar which is likely to be reactive to human triggers. Avalanches may be larger than expected due to the presence of this weak layer.

Snowpack Summary

Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.

40-60 cm. of recent snow is sitting on a very weak layer of surface hoar which has potential to surprise backcountry users by how easily it may be triggered and how wide the persistent slabs propagate across slopes. Recent avalanches on this layer have primarily been reported at treeline and below.

60-100 cm. down is an older surface hoar and/or a thin melt crust from mid January. This layer was more prominent in the north Purcells in sheltered, open slopes at treeline.

Deep persistent weak layers can still be found in the lower snowpack. These weak layers are most likely to be triggered from rocky areas with a shallow or thin to thick snowpack.

Terrain and Travel

  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
  • In times of uncertainty conservative terrain choices are our best defense.
  • Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
  • Be careful as you transition into wind affected terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Problems

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.

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.