Avalanche Forecast
Issued: Feb 24th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
ghelgeson,
Avalanche Canada
We're moving into a very stormy period which will be a great test for our snowpack, although it's "orange" Tuesday natural avalanches may become likely late in the day as new snow and wind form fresh slabs. Travel plans for Tuesday should have lots of mellow terrain options.
Summary
Confidence
Weather Forecast
Batten down the hatches, the storm train is coming.
MONDAY NIGHT: Freezing level around valley bottom, moderate to strong southwest wind, 5 to 10 cm of snow expected.
TUESDAY: Overcast, freezing level around 700 m, strong southwest wind, 5 to 10 cm of snow during the day, with another 10 to 20 cm expected Tuesday Night.
WEDNESDAY: Overcast, freezing level rising to about 1000 m, strong southwest wind, 5 to 20+ cm of snow during the day with another 10 to 20 cm Wednesday night.
THURSDAY: Overcast, freezing level holding around 1000 m, strong southwest wind, 10 to 30 cm of snow.
Avalanche Summary
On Sunday a few different observations of the avalanche cycle that occurred during (Feb. 21) and just after the last storm emerged. Natural avalanches were widespread to size 2.5 at all elevations, likely running on facets and surface hoar. Explosive control work Sunday produced avalanches to size 2.5 at alpine and treeline elevation bands. Glide crack openings and failures continue to be reported too.
On Saturday natural slab avalanches ran on the February 19th surface hoar producing avalanches to size 2 on north and northeast facing aspects at 1200 m. Storm slabs running on the surface hoar were sensitive to skier triggering between 1300 and 800 m, this is worth highlighting as these elevations are at and below treeline. Small loose dry avalanches were also reported in the Shames backcountry in this MIN report.
Snowpack Summary
40 to 70 cm of new snow has formed storm slabs at all elevations. The slabs are likely deepest in lee alpine terrain features, as upper elevations have seen a significant amount of strong wind from the southwest and even a bit of northwest in the last few days.
These slabs may slide easily where they overly a couple layers of surface hoar that may be found in sheltered terrain at and below treeline or a melt-freeze crust on sun-exposed aspects. You may find these layers around 50 and 80 cm deep.
A thin layer of weak and sugary faceted grains that formed in January may be found about 120 to 170 cm deep, and an early-season melt-freeze crust lingers at the base of the snowpack. These layers produced a few large natural avalanches in early-February but have recently been unreactive.
Terrain and Travel
- Watch for changing conditions today, storm slabs may become increasingly reactive.
- As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
- Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
- Be aware of the potential for human triggerable storm slabs at lower elevations, even on small features.
Problems
Storm Slabs
Storm slabs are a serious problem at all elevations, and we need to be extra cautious at and below treeline where up to 60 cm of snow rests on well-preserved surface hoar. The alpine is a different story, at that elevation the storm snow has been heavily affected by wind and slabs are 30 to 90+ cm in depth. Storm slabs may rest on a melt-freeze crust on sun-exposed aspects too. The deepest deposits will likely be in lee terrain features near ridges, as the snow fell with strong south to west wind. The train of coming storms will exacerbate all of these issues.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 25th, 2020 5:00PM
