Avalanche Forecast
Issued: Jan 23rd, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
jpercival,
Avalanche Canada
Strong winds and heavy snowfall will maintain the danger rating at high.
Seek conservative terrain choices that avoid avalanche terrain during this period.
New snow and a buried weak layer combined have the potential to produce very large avalanches.
Summary
Confidence
Moderate
Avalanche Summary
Sunday: A relatively quiet day for avalanche observations and reporting. Explosive control produced limited small (size 1 to 1.5) results.
Saturday: Numerous large (size 2) wind slab and storm slab avalanches have been reported. These avalanches were located on north aspect terrain between the elevation bands of 1400 to 1600 m. A few of them were naturally initiated with most being either explosive or ski-cut triggered.
Friday: Another round of ongoing avalanche occurrences has been reported, as visibility has been limited these reports suggest that many more have been occurring. Numerous both natural and explosive triggered large (size 2-2.5) have been reported. These avalanches have all initiated within the 1500 - 1600 m range just below ridgetop features. One very large (size 3) avalanche ran 1000 m in length and the common theme of running far and fast due to firm surface conditions has been a common theme. A rain-on-snow event triggered loose wet avalanches 1300 m and below.
On Thursday A naturally occurring and ongoing avalanche cycle was observed by numerous operations. Many of these avalanches were large (size 2). In the north of this forecast region, a very large natural wind slab avalanche (size 3.5) was reported.
Riders should exercise restraint and patience as the new and past storm instability requires time to settle and bond. Choose simple non-avalanche terrain that is low-angle and well-supported. Avoid steep and wind-loaded areas at upper elevations. Keep in mind the potential for deeper instabilities to produce large and surprising avalanches that will run far and fast.
Snowpack Summary
Last night's storm delivered amounts between 30 to 40 cm and has been redistributed by strong to extreme south wind. Expect at upper elevations, these southerly winds have scoured windward areas and redistributed this storm snow into wind slabs in lee areas. New storm snow now overlies the past 50 to 70 cm. Below 1000 m moist snow or a crust can be found at or near the surface.
A weak layer of surface hoar buried in early January is now down 30-60 cm. This layer is spotty in its distribution and is of greatest concern in sheltered and shaded openings at treeline.
Weak layers that were reactive over the Christmas and New Year's period have shown signs of bonding and gaining strength. These include a surface hoar layer buried on Dec 28 found 50 to 100 cm deep and a facet layer buried on Dec 23 found 70 to 120 cm deep.
Weather Summary
Monday night
Cloudy with snowfall, 5 to 20 cm of accumulation. Alpine temperatures -1 °C. Ridge wind west 80 km/h. The freezing level rises to 1000 m.
Tuesday
Cloudy with light snowfall, 1 to 5 cm of accumulation. Alpine temperatures are 1 °C. Ridge wind west 70 km/h. The freezing level rises to 1500 m.
WednesdayCloudy with rain and snowfall, 5 cm of accumulation. Alpine temperatures 2 °C. Ridge wind west 50 km/h. Freezing level 1800 m.
ThursdayCloudy with very light rain and snowfall, trace amounts of accumulation. Alpine temperatures 2 °C. Ridge wind west 50 km/h. The freezing level beginning to descend to 1200 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Dial back your terrain choices if you are seeing more than 30 cm of new snow.
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
Problems
Storm Slabs
Storm slabs will grow in size and sensitivity as the snowfall and wind increase. Expect the deepest and most reactive slabs to exist in wind-loaded terrain at upper elevations.
Keep in mind that storm slab avalanches have the potential to step-down to deeply buried weak layers, resulting in large and consequential avalanches.
Winds are expected to maintain at a sustained 80 km/hr. Expect wind slab to build adjacent to ridgetops, lower in the terrain, and for the downflowing wind to deposit snow near the base of steep cliffs and steep areas near ridgetops.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A series of storms have added a significant load to buried weak layers in the upper meter of the snowpack. The primary layer of concern is a layer of surface hoar now buried 30-50 cm deep. This layer is spotty in distribution and is not present on the very western boundary of the region. Primarily the PWL is found inland and most likely to be a concern in sheltered and shaded openings around treeline.
The second layer is comprised of facets and in isolated areas surface hoar that was buried in late December. This layer is now down 70-120 cm. It has shown evidence of strengthening but remains on our radar as active loading continues.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 24th, 2023 4:00PM
