Avalanche Forecast

Archived

Jan 7th, 2012–Jan 8th, 2012

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural and human triggered avalanches likely.

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.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

A polar warm front stalling north & west of the region will bring moderate to heavy precipitation to the surrounding areas Sunday. However, the Purcells will largely be "protected" from the action by a lingering ridge of high pressure. I expect scattered flurries in the region Sunday with snow amounts in the 5 - 10 cm range. Freezing levels rise to 1500m or so Sunday as the warm front affects the area. The trailing cold front associated with the system moves in late Sunday/early Monday bringing lower freezing levels and delivering another 5 -15 cm of snow. Expect strong SW winds at & above treeline Sunday with a daytime high of 0 C @ 1500 m.

Avalanche Summary

A few natural avalanches in the alpine to size 1.5 were reported from the region Friday. A skier was purportedly killed in an avalanche in the Molar area of the Dogtooth range near Golden on Friday, no details have been confirmed as of the writing of this forecast.

Snowpack Summary

The latest batch of storms has delivered around 50 cm of snow to the region. In some locations the new snow rests on top of a surface hoar layer buried January 3rd. Strong southwesterly winds have redistributed the new snow into windslabs that can be found on NW through SE facing slopes at and above treeline. Widespread crossloading is present throughout the region. A rain / melt/freeze crust formed by recent warm temperatures can be found as high as 1500m. The mid-December surface hoar layer continues to be a player, it's now buried 80 - 140 cm below the snow surface. Very weak snow near the ground is also a concern and while it has not been reactive recently, triggering a full depth avalanche near the ground is within the realm of possibilities right now.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.