Avalanche Forecast

After a mostly clear start to Saturday for much of the Cascades, a fast moving frontal system will bring light snow to the northeast Cascades by late morning and spread south to the central and southeast Cascades in the afternoon. New snow amounts through 4 pm will generally be light to insignificant, but westerly winds above treeline are expected spike up by mid-day. There is ample new snow available for transport along the east slopes closer to the crest. 

Wind slab should be the primary avalanche problem and mainly found near and above treeline Saturday. Wind slab should be less likely to trigger throughout the Cascades but look for wind loaded slopes further downslope than usual particularly in the Mission Ridge/Blewett area.

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. 

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 connected 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 slab 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.