Avalanche Forecast

A mix of sun, clouds and snow flurries for the next few days with the next low pressure moving in Sunday with minimal precipitation 

Friday Night: Mainly Cloudy, light and variable Northwesterly winds, freezing level 800 m. Alpine Low -10C / High -6C. 

Saturday: Cloudy with sunny periods and isolated flurries, light Southerly winds, freezing level 700 m. Alpine Low -10C / High -7C. Some areas may experience a Weak Alpine temperature inversion with cool valleys with clouds and slightly warmer temperatures above.

Sunday: Cloudy with snow flurries, AccumulationsTrace to 4cm (less to the north), light-moderate Southerly winds, freezing level 700 m. Alpine Low -10C / High -7C.

Monday: Cloudy with snow flurries, AccumulationsTrace to 4cm (less to the north), light-moderate Southerly winds, freezing level 700 m. Alpine Low -10C / High -7C. Freezing levels rise to 900m.

Avalanche hazard is highly variable and dependent on snowfall amounts and freezing lines experienced locally by this recent storm. Cooler temperatures and the passing of the storm mean that the natural avalanche cycle has tapered. However, reports continue to illustrate the poor bond of the new snow to buried surface hoar and rain crusts near the surface, particularly where there is more than 30cm of new snow.  

Reports of loose dry avalanches to size one from the steep terrain in the alpine and on steep solar slopes are further evidence of the poor bond of new snow to recent rain crust and sun crusts. Anticipate these releases, especially if the sun comes out or you are transitioning into steeper terrain.

There have been isolated reports of skier controlled small avalanches on the buried surface hoar. If and when more slab properties develop, we expect to see more reports like this. Larger skier controlled avalanches have been reported in wind loaded regions at ridge crests.

Earlier in the week at the peak of the avalanche cycle there were numerous reports of large (size 2) and very large (size 3-3.5) avalanches that ran natural and with explosive control, some running to valley bottom. Notably, on Wednesday avalanche control work was able to trigger large avalanches on the Nov 5 rain crust deep persistent layer in northerly shallow rocky terrain around 2000m in an adjacent region.  

Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN). Photos are especially helpful! Thank you so much for all the great MINs submitted so far!

The snowpack is highly variable demanding we are on the look out for where the snowpack structure remains weak: which is where a slab sits on top of buried surface hoar or crusts.   

The combination of heavy snow and rains with the warm storm earlier this week followed by cooler temperatures has reworked the snowpack. This storm deposited snowfall amounts of 20-40cm that fell on widespread large surface hoar and sun crusts on steep solar. Where this Surface Hoar layer is intact, you need to be wary of entering terrain where there are high consequences of a large Avalanche. 

We knew that prior to this storm this widespread large surface hoar was going to be an issue for a while. We suspect that heavy rains have made this layer less of an issue in many lower elevation areas (where it rained heavily). However, we KNOW this layer is still preserved in many tree line and below tree line locations which were not as affected by high freezing levels and rain events. In other words, if there is no THICK rain crust at and below tree line, be on the look out for buried surface hoar.  

Importantly, buried surface hoar is more preserved in the North and Eastern regions of the North Columbias, on cooler northerly slopes, and in some places where a thin rain /temperature merely "caps" intact crystals. From the far north region comes this MIN with reports of Rain up to 1500m and intact Surface Hoar. From Glacier National Park comes this MIN report from Dec 10 of intact Surface Hoar at 1600m at a below tree line location. We will continue to monitor this layer, because once slab properties develop (from warm temperatures or more snow) we may see it become more reactive.

Elsewhere, freezing rain with the recent storm has created a thick rain crust (or two) up to 2000m in the southern region of the forecast area. Its distribution and extent remains unclear - but we believe it is widespread in the southwestern portions of the North Columbias with reports of up 1- 5cm thick near tree line. In some areas there are two rain crusts: a thin crust near the base of the recent storm snow and a second thicker crust near the surface. See this MIN report from near Crowfoot Mountain & this MIN report from the South Columbia near Hall Mountain.  

In the Alpine, recent winds will have redistributed snow. These storm slabs sit atop suncrust on solar aspects. As ever, be aware of how direct sun is impacting steep solar slopes.

Down near the ground remains a thick rain crust with sugary facets above and below from early November rains (Nov 5 Crust). While we have not seen much reactivity on this layer, it continues to produce occasional Hard results in snow tests. It is most likely to be reactive to human triggers on shallow rocky slopes in the alpine or tee line "alpine-like" features or be triggered by a step down avalanche.

• Investigate the bond of the recent snow before committing to your line.
• Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
• Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
• In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.