Mt Hood

Mt. Hood has received a massive storm cycle over the past week, giving rise to very large and dangerous wind slabs at upper elevations. These slabs formed through Tuesday night, but with fresh wind transport Thursday night and Friday, you can still trigger them and the consequences of a slide would be severe. Avoid all wind-loaded slopes above treeline, recognizing that wind slabs may be difficult to identify under lower density snow, and limit time in drainages connected to large avalanche slopes on the upper mountain. In lower-elevation wind-sheltered terrain you might trigger a small or large avalanche on a steep rollover where you can feel denser snow layers just below the snow surface.

On Mt. Hood, evidence of active avalanche activity this week is abundant, although some of it may be slightly masked by new snowfall. With unusually cold temperatures, weak layers are slow to heal, maintaining the avalanche hazard elevated. Crowns from naturally triggered storm slabs have been up to 18” and loose dry avalanches are abundant and many can even be seen from Highway 26 and 35. Keep this activity in mind as you plan your tour and note avalanche activity in the areas you travel. Consider making travel plans that minimize time spent in canyons or gullies below large avalanche paths that have seen 5-6” of water in the form of snow over the last 6 days along with strong to extreme westerly winds.

With all this new snow, deep snow hazards exist at lower elevations and less wind-affected areas. Before heading out, learn about tree well or snow immersion suffocation risks and travel with a partner (www.deepsnowsafety.org). 

January 16th, 2020 (The regional synopsis is updated every Thursday @ 6 pm)

In the past week and a half, there have been five avalanche fatalities in three separate accidents in the US. One occurred near Kellog, ID and another outside of Baker City, OR. Local avalanche centers will perform accident investigations including final reports. You can find preliminary accident information at avalanche.org.

From January 9th to 16th the Pacific Northwest slid into deep winter. A cold and snowy regime brought a nearly continuous barrage of storms through the area. Temperatures bottomed out as modified arctic air made its way south from interior Canada, and many stations recorded the lowest temperatures of the season so far. A snowpack has been growing at lower elevations due to some lowland snow on both sides of the Cascades.  NWAC’s snow depth climatology report shows most stations have surpassed average depths on the ground for this time of year. Quite the comeback from two weeks ago, when most were at 25-64% of normal. 

Location

Total Snow Depth (in) 1/8/20

Total Snow Depth (in) 1/16/20

Hurricane Ridge

51

91

Heather Meadows Mt Baker

95

126

Stevens Pass

63

85

Snoqualmie Pass

33

77

Mission Ridge Mid Mtn

18

28

Crystal Mt Green Valley

66

92

Paradise Mt Rainier

105

138

White Pass Upper

69

110

Timberline

57

118

Mt Hood Meadows

53

98

Snow depths continued to rise. Total snow depths doubled in some locations.

The mountains went through a period of prolonged dangerous to very dangerous conditions as the snow kept coming. Many locations picked up over a foot of new snow per day for a number of days in a row, and storm slab instability was widely experienced across the region. At times, instabilities within new snow layers were very reactive, and you didn’t have to do much to provoke an avalanche. Many people triggered small to large soft slab avalanches, even well below treeline. The cold temperatures tended to preserve these instabilities longer than usual during this time. 

Small ski triggered storm slab near Mt Hood Meadows. January 11, 2020. Scott Norton photo.

This cold, low density snow was also susceptible to wind drifting as westerly winds buffeted the alpine zone from the 8th to the 15th. On the 15th the mean winds shifted, and a south and east wind event disturbed the powder on open, exposed terrain near the passes and at upper elevations throughout the region. This created wind slab problems in some unusual locations.

Wind slabs formed over the low density powder snow. Mt Baker Backcountry. January 15, 2020. Zack McGill photo.

Trailbreaking in undisturbed snow was often very deep and difficult. In most places at any point in the week you could step off your skis or machine and sink in up to your chest in deep powder snow. The deep snow presented hazards of its own such as tree wells, and made it very easy to get stuck on a machine or lose a ski. Many folks experienced excellent, deep powder conditions and stuck to conservative terrain choices. 

-MP

A cold winter’s day over the Chiwaukum Range, from Stevens Pass. Matt Primomo photo.