Avalanche Forecast

A warm front on Sunday night will be rapidly followed by another warm front on Monday. Strong southwest to west winds should be seen in the alpine with moderate to heavy rain or snow mainly Sunday night and  again by Monday midday with further warming. Snowfall so far in December by Monday morning along the west slopes should range from 1-4 feet which has been fairly evenly distributed but with the most at Mt Baker.

More new potentially large wind and storm slab will continue to be the focus on Monday along the entire west slopes. Back country travel in the near or above treeline is not recommended on Monday. Visibility will probably be poor on Monday with slab layers increasing making it difficult to avoid avalanche terrain.

Note that the west slopes do not have a uniform snowpack! The weather in late November is expected to have caused a persistent slab at Stevens and Snoqualmie Passes. Persistent slab is especially dangerous because it may be harder to trigger and propagate rapidly causing larger faster moving avalanches.

With less snow below treeline, wet loose snow avalanches will not be in the forecast. But change your plans if you find wet snow deeper than a few inches or see signs of wet loose activity such as pin wheels or natural wet loose avalanches.

Note that the discussion and forecast text is the same along the west slopes but the avalanche danger forecast varies by zone.

Weather and Snowpack:

We had a wet and wild November with about 12-25 inches of water at NWAC station along the west slopes only amounting to about 3 feet of snow in the north above 4000 feet and above 6000 feet elsewhere. This formed a strong crust in mid November all areas near and west of the crest.

Then strong high pressure led to strong temperature inversions and brought very cold air east to west through the Cascade passes mainly Stevens and Snoqualmie in late November. This caused widespread hoar frost and faceted snow near the November crust along the Cascade east slopes and east to west through the Cascade passes mainly Stevens and Snoqualmie.

The weather so far in December has gotten very active with heavy snowfall along the west slopes and an overall warming trend. 

This weather and snowpack scenario better get everyone's attention because it is a great set up for avalanches!

Reports:

New NWAC observer Simon Trautman was near the Mt Baker Ski Area on Saturday and reported reactive upside down P hardness snow slab over lower density 4f snow layers. He reported shooting cracks and numerous size 1-2 natural storm slab avalanches up to 15 inches on northeast slopes and some skier triggered storm slab avalanches on south to west slopes.

We have a report of a skier burial at Stevens Pass in Corona Bowl on Sunday. A party ducked a rope and traversed to mid slope and the skier triggered a 1-2 foot x 100 foot crown and was buried with her head at about 2 feet below the surface and was dug out in about 15-20 minutes. The avalanche was on a southeast facing slope at about 5000 feet and ran on the November crust. Control at the ski area Sunday also gave widespread releases of the recent snow mainly on northwest facing slopes with crowns to 25-30 inches also running on the late November crust.

A brief email report received by the NWAC indicates that the buried hoar frost from the Thanksgiving weekend is also present to some extent at Snoqualmie Pass.