Avalanche Forecast
Issued: Mar 16th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Loose Wet.
JSmith,
Avalanche Canada
Lingering wind slabs below ridgetops may remain reactive to human triggers. Strong solar radiation weakens cornices and often causes them to fall onto slopes and trigger large avalanches. Pay attention to what's above your head if the sun is out.
Summary
Confidence
Weather Forecast
Monday night: Clear, Moderate to strong northwest winds, alpine low -6 C, freezing level valley bottom.
Tuesday: Sunny, light to moderate northeast winds, alpine high 2 C, freezing level 1100 m.
Wednesday: Mix of sun and cloud, light northwest winds, alpine high 1 C, freezing level 1000 m.
Thursday: Sunny, light to moderate southeast winds, alpine high temperature 1 C, freezing level 1000 m.
Avalanche Summary
During the arctic outflow winds, operators reported small to large (size 1-3) wind slab avalanches releasing naturally in lee terrain features at treeline and alpine elevations. There were numerous reports of avalanches releasing on persistent weak layers last week. Several of these avalanches were remotely-triggered. Check out this MIN from the Shames area as one example.
Snowpack Summary
Several days ago, strong arctic outflow winds formed wind slabs in a reverse-loading pattern. Last week's storm delivered 30-60 cm of new snow to the region with strong southwest winds creating ample snow available for wind transport. The recent snow is sitting on a weak layer of surface hoar buried 30-60 cm deep in many areas, especially in sheltered areas at treeline and below treeline. See this MIN from the Shames area that shows this layer when it was on the surface. Observers have reported widespread whumpfing and propagation in snowpack tests on this March 9th surface hoar, confirming its propensity for human triggers.
There are several additional layers of surface hoar that are now buried 70-120 cm and 110-160 cm deep that may also be the most prominent around treeline. On south through west facing slopes, this surface hoar may be sitting on a crust, which may increase the potential for triggering avalanches on these layers.
A weak layer of facets that formed in January may be found about 150 to 200 cm deep, and an early season melt-freeze crust lingers at the base of the snowpack. These layers have produced a few very large natural and explosive triggered avalanches over the past two weeks. Sunday's warm-up may have the potential to re-awaken these deeper layers.
Terrain and Travel
- Extra caution for areas experiencing rapidly warming temperatures for the first time.
- Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
- Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
- The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Problems
Wind Slabs
Strong outflow winds have drifted recent snow into wind slabs in a reverse loading pattern that may remain possible to human trigger.
Aspects: East, South East, South, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Multiple surface hoar layers have been buried by successive storm events and have shown continued reactivity to human triggering. These layers can be found buried 35-50 cm, 70-120 cm, and 110-160 cm below the surface. These weak layers are most problematic at treeline elevations where the surface hoar is well preserved. Rapid warming is expected to increase the likelihood of triggering deeper layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Loose Wet
Strong solar radiation may trigger a natural wet loose avalanche cycle on steep solar aspects.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 17th, 2020 5:00PM
