Warmth remains the primary driver of avalanche hazard as we shift into a more spring like pattern. Minimize your exposure to large slopes if the snowpack is becoming moist or wet.
Weather Forecast
Thursday: Freezing starting near 1000m, rising to about 1600m in the afternoon. Partly cloudy skies. Light variable winds at all elevations. No significant precipitation expected.Friday: Freezing level starting at valley bottom, rising to about 1700m throughout the day. Mostly clear skies. Moderate SW winds all elevations. No significant precipitation expected.Saturday: Freezing level hovering around 1500m. Moderate SW winds at treeline, strong SW winds at ridgetop. Scattered cloud. No significant precipitation.
Avalanche Summary
No new activity to report from Tuesday. On Monday a few large avalanches were reported: Our field team was in the Crown Mountain area where they noticed a large slab avalanche on an extreme E/NE face that was likely triggered by cornice fall. In the neighboring Waterton region cornice failure resulted in two large avalanches that stepped down to the mid-February interface on NE facing features at 2400m. On Saturday in the neighboring Lizard Range cornice fall produced a size 2.5 avalanche.
Snowpack Summary
Both Monday and Tuesday brought good overnight temperature recovery to the region with temps getting down to +0.8c at 960m. These colder temps are forming a surface crust that should become supportive if it isn't already. On Wednesday ridge-top transport of snow was observed which is likely resulting in wind slab formation in the alpine. The snowpack is reportedly isothermal as high as 2000m at this point and even the highest elevations are probably not far off. The mid-March rain crust is down 35 to 70cm and has shown a good bond with snow above. Old persistent weak layers are still intact in the mid and lower snowpack and there may be potential for these layers to wake up with a big cornice fall, sustained warming and/or a significant rain event.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.