Avalanche Forecast

Issued: Jan 19th, 2014 8:54AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Deep Persistent Slabs and Wind Slabs.

jlammers, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

A ridge of high pressure will continue to dominate the region bringing dry conditions for the forecast period. An inversion is likely on Monday with valley cloud, clear skies above and alpine temperatures hovering at about 0.0. On Tuesday and Wednesday expect increasing high cloud and freezing levels at about 1400m. Winds should remain light out of the west/northwest for the forecast period. No significant precipitation is expected for at least a week.

Avalanche Summary

On Friday explosives avalanche control produced at least 3 size 3 slab avalanches which failed to ground in steeper alpine terrain. 2 size 3, and 1 size 3.5 natural slab avalanches were also noted. At least 2 of these failed at ground level. All avalanches observed failed on a variety of aspects.On Saturday explosives avalanche control in the Northwest of the region produced a few windslab avalanches to size 1.5 at treeline and in the alpine. No other avalanches were reported on Saturday.

Snowpack Summary

Between 60cm and 90cm of well settled storm snow exists as a stubborn hard wind slab in many exposed areas. Thanks to recent warming, steep, sun exposed slopes have seen a daily melt-freeze cycle while surface hoar has been growing in some shaded terrain. Below the recently formed storm slab you may find surface hoar buried around January 8th, although no recent avalanche reports have been attributed to this layer. In the mid to lower pack you may find a surface hoar layer buried in mid December. Further down you may also find the December facet/crust combo. These layers are likely gaining strength, but professional operators are treating them with caution.The biggest concern throughout the region is a layer of weak sugary depth hoar at the base of the snowpack which may coexist with a crust which formed in October. I would continue to be suspicious of any large or unsupported upper elevation slopes, especially if they haven't already avalanched. Possible triggers include a heavy load over a thin spot, a cornice fall or rapid temperature change. Any avalanche failing at this interface would be highly destructive.

Problems

Deep Persistent Slabs

I would continue to be suspicious of any large or unsupported upper elevation slopes, especially if they haven't already avalanched. Although they have become less likely, any deep persistent avalanche would be highly destructive.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.>Caution around convexities or areas with a thin or variable snowpack.>Conditions have improved, but be mindful that deep instabilities are still present.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 6

Wind Slabs

Some operators are still expressing concern for wind slabs that were formed last week. Although they may have gained considerable strength, triggering may still be possible in steep, unsupported terrain.

Watch for areas of hard wind slab in steep alpine features.>Be aware of the potential for wide propagations due to the presence of hard windslabs.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely

Expected Size

1 - 3

Valid until: Jan 20th, 2014 2:00PM