Avalanche Forecast

Fair - Intensity of incoming weather systems is uncertain on Wednesday

The high pressure system of late weakens and gives way to a series of Pacific frontal systems.Tuesday: Mainly cloudy, no precipitation, alpine temperatures -8, moderate northwest easing to light west winds.Wednesday: A Pacific frontal system starts to affect the interior regions. Cloudy with light to locally moderate snowfall, moderate to strong west winds. Freezing level in the valley bottom.Thursday: Light snowfall, Alpine temperatures -7, moderate west winds.

Reports continue to roll in about the extent of the avalanche cycle from last Thursday and Friday. While the large avalanches likely dug into deeply buried weak layers, it appears as though much of the activity was limited to the storm snow or the mid December surface hoar. More recent natural avalanche activity seems to be isolated to a windslab and cornice releases up to size 2.5. These are running within the storm snow in the alpine and at treeline elevations. There was also a report of a glide crack release running naturally to size 3.

Last week's storm delivered 20 - 50 cm of new snow bringing the average regional depth to 160 - 240cm. This new snow lies on top of old wind slabs, a thin melt freeze crust below 2100m and numerous weak layers. Down 40 -100cm is the mid December layer comprised of surface hoar, stellars and/or a crust. Around 70 -140cm down is the early December surface hoar, faceted snow and/or crust.There are two deeper layers of note. The late-November persistent weak layer consists of a sun crust on steep south facing slopes and surface hoar in sheltered areas and is now buried 90-160cm below the surface. The October deep persistent weak layer consists of a layer of facets sitting on a crust at the base of the snowpack. This layer is predominantly found on northerly aspects at treeline and in the alpine. The depth of both these layers makes directly triggering an avalanche on them unlikely (maybe a heavy load on a thin spot in steep terrain). Their presence could, however, increase the size of a potential avalanche through step-down.