Avalanche Forecast

A passing front overnight should move south of the Cascades by early New Year's Day. Generally light to moderate amounts of new snow accumulation are expected by Sunday, however strong and shifting winds should redistribute any available surface snow to a variety of aspects. 

New or lingering wind slabs should be the primary avalanche problem and mainly found near and above treeline New Year's Day. Strong and gusty winds and very low density snow may deposit snow further downslope than usual and on a variety of aspects.

The persistent slab problem still warrants attention in the Mission Ridge/Blewett area where several PWLs represent a touchy snowpack. Remember that persistent weak layers are generally involved in larger avalanches. Avoid steeper slopes in areas where you still find this layer in snow pits or especially if you experience direct observations of this layer such as whumpfing or shooting cracks. 

Weather and Snowpack

Strong storms around the Solstice deposited generally half to 1 inch of water equivalent along the east slopes. Storm totals generally ranged from 6 to 12 inches. 

A strong front and strong west flow aloft was seen over the Cascades on Monday and Tuesday. NWAC and Snotel stations along the east slopes had 4 to 18 inches of new snow through 48 hours ending Wednesday morning along with a cooling trend. The higher amounts were seen closer to the crest while the lower amounts represented the Blewett/Mission area.   

A warm front kept light snow and moderate winds going through much of day in the Washington zone Thursday before pushing south Thursday night. 8-12 inches of snow fell in the Washington Pass zone, Holden and Lake Wentachee while 1-2 inches accumulated further east toward and Blewett/Mission area and further south. 

Clearing Friday night allowed areas of surface hoar to form in some zones below tree line, reported in the Washington Pass area Saturday.

Recent Observations

In the Delancey Ridge area in the Northeast zone Thursday, NCMG reported the new snow totaled 15-20 cm (6-8 inches) through the afternoon but was lacking a slab structure near and below treeline. In the same area Friday, small loose dry avalanches were the primary avalanche problem, but wind affected snow surfaces were visible above treeline. Besides loose dry avalanches in steep terrain, no evidence of natural avalanche activity was observed. In the Washington Pass zone, the 12/17 PWL has been found to be unreactive and has been removed from the set of avalanche problems.  

A different story continues in the Mission Ridge/Blewett area.

Last week Mission Ridge ski patrol produced 1.5 to 3 ft hard slab avalanches during control work. These avalanches were releasing on basal facets about 15 cm from the ground. 

On Saturday 12/24, a backcountry ski tourer in the Lake Clara area near Mission Ridge reported a huge whumpfing noise, likely indicating a collapse of the basal facets. While no avalanche occurred, the terrain where the collapse occurred connecting to a large avalanche path that was NE facing near treeline. 

Two reports from the NWAC observation page tell the continuing story of a much shallower snowpack with multiple persistent weak layers in this portion of the central-east zone. 

Tom Curtis was out at Mt. Lillian Friday and found reactive wind slabs along ridges with shooting cracks and whumpfing on north aspects near 5900 feet.  The wind slab was likely collapsing down to the 12/17 Persistent Weak Layer (buried surface hoar) about 25-35 cm down. Wind slabs were found on NW-E-SE aspects with some wind loading apparent well below treeline.

Touring in the Washington Pass area Saturday reported no results from hand shears in the near and below treeline bands and no avalanches while avoiding possible wind loaded terrain above treeline. Nice, low cohesion surface snow conditions were reported below treeline.