Plan your day around avoiding sun-exposed slopes and cornices at peak daytime warming when the avalanche danger is expected to rise to MODERATE.
Summary
Confidence
Weather Forecast
A gradual cooling trend begins
Tuesday night: Partly cloudy, strong northwest wind, alpine temperature near 0 C, freezing level dropping below 1800 m.
Wednesday: Mix of sun and cloud, strong northwest wind, alpine high temperature near 0 C, freezing level dropping to 1000 m overnight.
Thursday: Mainly sunny, light northeast wind with moderate ridgetop gusts, alpine high temperature near 0 C, freezing level rising to 1500 m.
Friday: Mostly cloudy, light variable wind, alpine high temperature -2 C, freezing level rising to 1200 m.
Avalanche Summary
Numerous large to very large (size 2-3) natural and explosive-triggered wet loose and wet slab avalanches were reported over the weekend across elevations. A couple of natural cornice failures on northeast alpine slopes triggered very large (size 3) avalanches on slopes below. Glide avalanches have also been reported.
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. 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. Check out the Forecaster's Blog for information on how to manage these spring conditions.
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.
Glide cracks releasing as full depth glide slab avalanches become more common in the spring and are extremely difficult to predict. Best practice is to avoid slopes with glide cracks.
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. Multiple very large wet slab avalanches have been observed in the last couple 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, West, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Apr 21st, 2021 4:00PM
