Avalanche Forecast
Issued: Dec 27th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
lbaker,
Avalanche Canada
On Tuesday explosives control produced numerous large destructive avalanches on the persistent weak layer.
Human-triggered storm slab avalanches may step down to deeper layers resulting in high-consequence, large, destructive avalanches.
Summary
Confidence
Avalanche Summary
On Tuesday, Explosives control produced several persistent slab avalanches, up to size 3. This is evidence that with the persistent weak layer is still with us and will result in large destructive avalanches with the right trigger.
On Monday, evidence of a natural avalanche cycle, both wet slab, and wet loose avalanches, was observed on all aspects at all elevations. Avalanches were up to size 3 and likely occurred during the rain event Sunday night.
On Sunday, explosives control triggered several storm slab avalanches up to size 2.5. Storm slabs were 30-50 cm deep. Explosive also triggered one size 2.5 persistent slab avalanche that is suspected to have run on the Dec 8 surface hoar.
Please continue to post your observations and photos to the Mountain Information Network.
Snowpack Summary
40 - 50 cm of storm snow has fallen since Dec 22. Extreme southerly winds have pressed surfaces and redistributed snow into thick slabs in alpine lees. A melt-freeze crust is found below 1800 m. The new snow covered a layer of weak and unconsolidated snow produced by the recent cold weather.
A number of layers persist deeper in the snowpack, consisting of facets, surface hoar, and crusts. Most recently, these layers have been unreactive and this heavy load of new snow should provide insight into any deeper instabilities. Total snow depths are roughly 90-140 cm at treeline and up to 200 cm in the alpine.
Weather Summary
Tuesday Night
Precipitation continues tonight with another 10-20 mm. Variable 25 km/h winds. Ridgetop low temperature -7. Freezing levels 800 m.
Wednesday
An additional 2 - 5mm of precipitation diminishes in the morning. Southwesterly 40 km/h winds easing to 20 km/h in the afternoon. Ridgetop high temperature -7. Freezing levels 800 m.
ThursdayScattered flurries, 10-20 mm. Southerly 40 km/h winds increasing in the afternoon. Ridgetop high temperature -4. Freezing levels hover from 500 -1000m.
FridayCloudy with flurries, 15 - 25 mm. Westerley 20 km/h winds. Ridgetop high temperature -4. Freezing levels hover near 800 - 1300 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
- Be alert to conditions that change with aspect and elevation.
Problems
Storm Slabs
Extreme southerly winds have redistributed upwards of 50 cm of new snow into deep pockets at higher elevations. Where snow remained dry expect to find pockets of storm slabs that are reactive to human traffic. Be especially cautious transitioning into wind-loaded terrain, more reactive deposits lurk in leeward features.
If triggered storm slabs may step down to deeper layers resulting in very large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A crust with weak, facetted snow above and below is buried by roughly 50-150 cm of snow. On Tuesday explosives control triggered numerous on this layer. Above 2000 m avalanches broke under the crust and stepped down to deeper layers resulting in large avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 28th, 2022 4:00PM
