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

Jan 28th, 2019–Jan 29th, 2019

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

Regions

Purcells.

The snowpack in the Purcells this season is exceptional, and not in a good way. We've summarized our thoughts on this precarious snowpack in the latest forecasters blog here. Take it easy out there, this is not the time for the big lines.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

High pressure, cold temperatures and clear skies should allow for great travel and visibility Tuesday. Cloud cover starts to build back in Wednesday ahead of two storm pulses that should deliver a bit of snow beginning on Friday.MONDAY NIGHT: Freezing level at valley bottom, light northerly wind at most elevations with moderate northwest wind at ridgetop, no precipitation expected.TUESDAY: Clear skies, freezing level at valley bottom, light variable wind, no precipitation expected.WEDNESDAY: Broken cloud cover, freezing level at valley bottom, mostly light variable wind with moderate northwest wind at ridgetop, no precipitation expected.THURSDAY: Scattered cloud cover, freezing level at valley bottom creeping up towards 1000 m in the afternoon, light variable wind, trace of snow possible.

Avalanche Summary

Wind slabs to size 2.5 were observed Sunday on north, northeast, south and southwest facing terrain features between 1900 and 2800 m. These are likely the wind slabs that formed Saturday night.On Thursday explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a great MIN report from January 22nd that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check it out here.

Snowpack Summary

Saturday delivered warmth and strong to extreme wind out of the south, southwest and northwest. This left a robust crust (up to 4 cm thick) on steep south facing aspects and redistributed snow into potentially deep wind slabs in lee alpine features. The warmth also allowed 10 to 50 cm of snow to settle into a well consolidated slab above the mid-January persistent weak layer (PWL). This PWL is made up of large surface hoar that is most prevalent at and below treeline. On steep solar aspects this interface presents as a crust, there may be locations where the surface hoar actually sits on the crust.The snowpack is also harboring a nasty weak layer near the ground that is made up of weak faceted grains above a crust. This interface continues to produce sporadic avalanches that are very large and destructive. Avalanches triggered on this weak layer take the entire seasons snowpack with it and have resulted in numerous close calls and serious incidents. This layer is most likely to be triggered from zones where the snowpack is thin and weak. Rock outcroppings and ridge crests around large open slopes and bowls in the alpine are particularly suspect

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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.