Start (and finish) your day early and avoid sun-exposed steep terrain. Steer clear of cornices overhead and plan your egress route carefully.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to difficult to forecast freezing levels.
Weather Forecast
Sunday night: Clear, moderate southeast ridgetop wind, alpine temperatures near 0 C, freezing level dropping to 1100 m.
Monday: Sunny, moderate southeast ridgetop wind, alpine high temperature +2 C, freezing level 2000 m.Â
Tuesday: Sunny, light northwest wind, alpine high temperature +2 C, freezing level 2100 m.Â
Wednesday: Mix of sun and cloud, light northwest wind, alpine high temperature near 0 C, freezing level 1800 m.
Avalanche Summary
As the spring diurnal cycle continues, there have been reports of numerous large (size 2) wet loose avalanches on south-facing slopes at all elevations and a few large (size 2-2.5) cornice failures on a variety of aspects.Â
One wet slab was suspected to have released on the November crust layer on a shallow west aspect in the alpine, triggered by a loose wet avalanche from above. Triggers, such as cornice fall, loose wet avalanches, or a rider hitting a thin spot in the snowpack, are particularly concerning on steep, rocky slopes with a shallow or thin to thick snowpack as they are the most likely ways to trigger deeply buried weak layers.
Snowpack Summary
The snowpack has been undergoing a melt-freeze cycle with successive days of warm sunny weather. Strong solar radiation and warming will likely initiate wet loose avalanches as the snow loses cohesion. As the heat penetrates deeper into the snowpack, operators have reported larger wet slab avalanches. These avalanches are dense, destructive and can run far, reaching otherwise snow-free valley bottoms. Check out the Forecaster's Blog for information on how to manage these spring conditions.Â
Cornices are large and looming along ridgelines. Sun and warm temperatures will increase the chances of cornice failures, especially when temperatures remain above zero overnight.
The snowpack is overall strong and settled in most areas, however, sustained warming can increase the likelihood of large avalanches failing on deeply buried weak layers. This is most likely to occur on steep, rocky alpine slopes with a shallow or thin to thick snowpack.
Terrain and Travel
- Avalanche hazard is expected to to increase througout the day, think carefully about your egress.
- Back off slopes as the surface becomes moist or wet with rising temperatures.
- As surface loses cohesion due to melting, loose wet avalanches become common in steeper terrain.
- Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
Problems
Wet Slabs
The likelihood of wet slab avalanches increases during prolonged periods of warm temperatures, as the heat penetrates deeper into the snowpack. A couple large wet slab avalanches have been observed over the last few days. These avalanches are dense, destructive, and can run far, reaching otherwise snow-free valley bottoms.
Wet loose avalanche activity can also be expected on sun exposed slopes and below treeline. These avalanches are generally smaller than wet slabs but they can gather mass as they travel and reach low elevations.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Strong solar radiation and warming will likely trigger the large cornices that hang over ridge lines. Cornice falls are a hazard on their own, but could also trigger large avalanches on the slopes below.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Apr 19th, 2021 4:00PM
