Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to 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.

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.

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.

• 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.