Avalanche Forecast

Update Monday morning for the central east and southeast zone: The NWAC Blewett Pass and Mission Ridge stations, the Mission Ridge pro-patrol and Snotels in the southeast Cascades report 1-3 feet of new snow on Monday morning. Further moderate to heavy snow seems possible in these areas Monday morning. Along with strong E-NE winds this should make new wind slab likely or very likely on lee mainly west to south slopes. Storm slab is also likely or very likely on most slopes. The avalanche forecast for these areas will be updated to high in the near and above treeline and considerable in the below treeline in the central east and southeast zones.

In the northeast zone:: snow showers should give way to clearing skies and continued cold temperatures. Strong NE-E ridgetop winds should continue to transport the ample loose surface snow and build touchy wind slabs on more non-traditional or unusual SE-SW aspects, mainly above tree line and possibly near tree line.

Deep, low density snow will make sluffs or loose slides likely on steep wind sheltered slopes. Watch for travel on steep slopes above terrain traps, such as cliffs or creeks where the entertainment of loose snow may bury someone caught more deeply. 

Fresh, touchy wind slabs near ridges and non traditional aspects, will be the primary avalanche problem on Monday. Wind affected snow should be widespread Monday, especially with strong shifting winds, watch for wind transported snow on a variety of aspects and cross loaded features.

Along all of the east slopes the 12/17 PWL persistent slab problem is gaining strength, becoming more deeply buried and less sensitive in snowpack tests. However, continue to avoid large open terrain in areas where an overall shallow snowpack exists, or where you find this layer in snow pits, especially if you experience direct observations 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 series of storms beginning last Monday have deposited 1-2 feet of snow over most east slope areas through Friday. 

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

A deep cold low pressure system has added another 5-15 inches of snow through New Year's Day. With the exception of crest level and exposed ridges, this recent snow has accumulated with a cooling trend and little wind effects. 

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.  

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 skier 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. 

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. 

On New Year's Day, reports from multiple snow pits by Mission Ridge patrol testing the basal facet layer, now indicate a much stronger more settled snowpack from a week ago. The basal facets remain intact, but show signs of rounding and overall consolidation and bonding.