Avalanche Forecast
Issued: Mar 1st, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
swerner,
Avalanche Canada
There is still the potential to trigger persistent weak layers. These are producing large and consequential avalanches. A conservative mindset and patience are required.
Fresh wind slabs may be reactive to human triggers on northeast and east slopes.
Summary
Confidence
Weather Forecast
Tuesday: Cloudy with a trace of new snow. Ridgetop wind 50 km/hr gusting to 75 km/hr from the southwest and alpine temperatures near -5. Freezing levels valley bottom.
Wednesday: A mix of sun and cloud. Ridgetop wind strong from the southwest and alpine temperatures near -4. Freezing levels 2000 m.
Thursday: A mix of sun and cloud and freezing levels rising to 2000 - 2500 m.
Avalanche Summary
We received no avalanche reports on Sunday.
Our primary avalanche problem is persistent slabs. The persistent slab is down 40-100 cm and mostly found around treelne elevations. It is likely to trigger by the weight of a skier or sledder, initiating large and consequential avalanches. Almost daily we've received reports of skier and rider-triggered persistent slab avalanches from the SoRo and Lizard forecasting regions. These avalanches have been size 2 or larger and have caught people by surprise. This problem is not healing quickly and the conditions are not easily managed. A conservative mindset and patience are crucial right now.
New wind slabs may exist on East to Northeast aspects on Tuesday and loose-dry avalanches may spill from steeper terrain features, especially when the sun is out.
Snowpack Summary
Extreme ridgetop wind from the West has formed wind slabs in exposed terrain at treeline and alpine elevations. Loose-dry surface sluffing may occur from steep terrain features. 40 to 60 cm (in some places up to a meter) of snow now sits above sugary faceted snow that formed mid-February. Snowpack testing done by the South Rockies field team on Saturday in the Mear Lake area showed a relatively easy to moderate failure on the mid-Feb layer which propagated across the whole column (ECTP 13 down 40 cm). This indicates that a persistent slab can be triggered by the weight of a person and produce a consequential avalanche. This test was on a south-facing slope at treeline.
Deeper in the snowpack (50 to 90 cm deep) is yet another weak layer that was buried at the end of January. This layer consists of surface hoar, faceted grains, and/or a hard melt-freeze crust. On Wednesday a rider-triggered avalanche size 3 was reported on this interface. Check out this MIN report from Ruault Lake area in the western flank of the region.
Weak faceted grains and a decomposing melt-freeze crust can be found near the base of the snowpack.
Terrain and Travel
- The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
- Choose simple, low-angle, well supported terrain without convexities.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Problems
Persistent Slabs
Two layers of concern exist and have been reactive over the past couple of days. The upper layer being buried mid-February down 30-60 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 50-90 cm and consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. Avalanches have occurred on surprisingly shallow slope angles and the layer can easily be remotely triggered.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Wind Slabs
West to southwest wind has formed reactive wind slabs on leeward slopes. These could be triggered by the weight of a skier or rider, especially on east-northeast aspects.
Large looming cornices exist along ridgelines and require a wide berth from above and below, especially if they're baking in the sun.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 2nd, 2021 4:00PM
