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

Lizard-Flathead.

Slab avalanches are primed for skier and rider triggering. Remote triggering (from afar) is concerning and catching people by surprise. Conservative terrain choices are a great way to handle a persistent slab avalanche problem. 

Confidence

High - The number, quality, or consistency of field observations is good, and supports our confidence.

Weather Forecast

Overnight Thursday: Cloudy with snow 5-10 cm. Ridgetop wind light to moderate from the West. Alpine temperatures near -7 and freezing levels at valley bottom. 

Friday: A mix of sun, cloud, and flurries accompanied by a strong West wind. Alpine temperatures near -3 and freezing levels rising to 1000 m.

Saturday: Snow 3-5 cm. Moderate westerly wind. Alpine temperatures low at -20 and a high of -10.

Sunday: Snow 5-10 cm. Ridgetop wind switching to the East and blowing in the light values. Alpine temperatures low of -28 and high of -20.

Avalanche Summary

No new observations by publish time on Thursday.

On Wednesday, numerous natural storm slab avalanches were reported up to size 2, and several more slabs were triggered by explosives up to size 1.5. Loose-dry avalanches were seen up to size 1. 

The persistent slab proved to be reactive on Wednesday with skier and rider remote triggers and naturals up to size 2. Check out the awesome MIN posts here: MIN report, MIN report, MIN report. Sending a big shout out of appreciation to everyone posting these MIN's and sharing this pertinent information.

As natural avalanche activity tapers, wind and persistent slabs are still be primed for triggering. These will likely propgate far and can catch you by surprise even in low angle terrain. 

Snowpack Summary

Up to 60 cm of recent snow has formed a cohesive and reactive slab that sits above a weak interface of surface hoar and surface facets (weak sugar or feather-like snow crystals) and a crust that was buried late January. This slab of recent snow sits on top of a plethora of old snow surfaces comprising of hard wind slab, scoured areas, sastrugi, and isolated pockets of soft snow. Below 1800 m a hard melt-freeze crust underneath the new snow is found and a surface crust now exists up to 1700 m from the high freezing levels on Tuesday. 

A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which are currently unreactive. 

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Avoid terrain traps where the consequence of any avalanche could be serious.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.