Sawtooth & Western Smoky Mtns

The combination of new snow and wind will build slabs and cause the avalanche danger to rise throughout the day. Danger will likely increase to CONSIDERABLE overnight. Be on the lookout for slabs near features that slow the wind down like ridges and mid-slope gullies and ribs. In the past week, layers of weak snow buried in the snowpack have produced slab avalanches breaking 1-2 feet deep. These are most likely where the wind has been building slabs but are possible in sheltered terrain as well. Rain on dry snow at lower elevations will increase the threat of loose snow avalanches as the day progresses.

COVID-19: Please recreate responsibly close to home. The medical system cannot spare the resources to care for backcountry skiers and snowmobilers. Follow social distance requirements to protect yourself and others. 

The month of March has been marked by unsettled spring weather. Much of our forecast area received measurable amounts of precipitation on 10 of the past 29 days. It looks like today we will make that 11 out of 30. In between these stormy days we've seen patchwork skies with a mixture of sun and clouds depending on your location. Let's take a minute to think about how this affects the snowpack:

Intense spring sunshine can quickly melt fresh snow. After this wet snow refreezes, this process tends to result in a strengthening of the snowpack. Simple enough. However, when the sun starts to melt the snow but clouds put a halt to the process something else happens. A thinner, more fragile crust is left behind in this case, often accompanied by some small, angular snow crystals known as facets. Warm ambient air temperatures can also build these sorts of layers. Periods of storms followed by periods of partly cloudy skies left behind layers of crusts and facets that are buried in the snowpack. Light snowfall yesterday helped to bury another set of these layers and continued snowfall and wind drifting today will add stress to the underlying snow. 

The tricky thing is that these layers have proven to be variably reactive. Why is that? Our forecast area spans quite a large chunk of terrain, over 3000 square miles. On any given day, the weather varies significantly across this area. Passing clouds might provide some cover for one mountain while the sun is shining brightly on a neighboring mountain. But the weather isn't the only important factor in this equation. The direction a slope faces and the steepness of the slope both affect how much incoming solar radiation hits the slope. Because of these factors, the character of the weak layers that are buried in the upper portion of the snowpack varies from slope to slope. In some areas, the bonds at these interfaces are strong enough to support the slab on top of them, but in others they are not. On Saturday, skiers in the Smoky Mountains found an area where this interface was weak when they triggered an avalanche on a sheltered, north-facing slope.

Today will be a transitional day for the snowpack in our region. By tomorrow morning many areas will have been hit with a more substantial load than they have seen in weeks. This new snow will be accompanied by increasingly intense winds, a great combination for building wind slabs and adding weight to the snowpack. This loading event will help resolve just how widespread and reactive the weak layers in our snowpack are. If you decide to head out today, particularly this afternoon, I'd recommend dialing back your terrain choices and treat these layers as guilty until proven innocent.