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Avalanche Forecast

Archived

Mar 18th, 2019–Mar 19th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

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The snowpack is undergoing a major thaw. Large and dangerous natural wet avalanches are possible. This is a good time to step back, and allow the mountains to make the transition. 

Discussion

Snow and Avalanche Discussion:

After a prolonged cold and snowy period, and in some cases record breaking snowfall (Wenatchee and Yakima), we are experiencing a heat wave with record high temperatures. The snowpack is making a transition from cold and dry, to a spring-like pack. Meltwater is beginning to make its way through the upper snowpack. Along with this, there is a high degree of uncertainty regarding avalanche size over aspects and elevations. The only dry snow left is on direct north facing slopes, elsewhere wet snow is commonplace. Cornices are beginning to sag and break off. The most active period for wet avalanches will likely be late in the afternoon.

The proof is in the avalanches. Observers have reported wet loose avalanches the past few days on a variety of slopes, some big enough to bury or kill a person. A significant avalanche cycle occurred in Tumwater canyon with avalanches on almost all aspects with avalanches running as recently as Sunday and closing Highway 2. A widespread wet loose cycle continues in Icicle Creek through the 18th, with slides starting on northeast aspects above 7,000ft, and many at lower elevations. On Monday, I went to Swakane Canyon to have a look, and found many, more recent full depth wet loose slides right next to older slabs, that had also run on the ground.

 

The heat wave is on. Temperature graph from early March through current.

Snowpack Discussion

Coming soon.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.