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BACKCOUNTRY AVALANCHE FORECAST

WEST SLOPES SOUTH - SOUTH OF I-90 TO COLUMBIA RIVER

ISSUED
Saturday, January 18, 2020 - 6:16PM Sat, Jan 18, 2020 - 6:16PM
AUTHOR
Andy Harrington
THE BOTTOM LINE

We have a large amount of uncertainty about how the weather forecast will play out on Sunday. Avalanche hazard typically peaks during periods of rapid change, so make time for snowpack and weather observations throughout the day. You may experience changing conditions as the day proceeds with warm, wet weather changing the snow stability and avalanche character in a number of ways.

AVALANCHE DANGERi

Sunday, January 19, 2020
Above Treeline Considerable (3)
Near Treeline Considerable (3)
Below Treeline Considerable (3)

OUTLOOKi

Monday, January 20, 2020
Moderate (2)
Moderate (2)
Moderate (2)

OUTLOOKi

Monday, January 20, 2020
2 2 2
Danger Scalei
  • Low (1)
  • Moderate (2)
  • Considerable (3)
  • High (4)
  • Extreme (5)

AVALANCHE PROBLEM #1i

  • Storm Slab

    Avalanche Problemi
  • Above Treeline
    Near Treeline
    Below Treeline
    Aspect/Elevationi
  • Unlikely
    Possible
    Likely
    Very Likely
    Almost Certain
    Likelihoodi
  • Small (D1)
    Large (D2)
    Very Large (D3)
    Historic (D4-5)
    Sizei
Photo for Storm Slab

Shooting Crack in Storm Snow (1/16/2020)

Warming temperatures on Saturday started to transform our cold dry snowpack and recent snow into heavier storm slabs sitting atop lighter snow. Further warming and more precipitation on Sunday may continue to develop this upside-down snowpack structure, maintaining dangerous avalanche conditions on slopes greater than 35 degrees. Areas of wind deposited snow still linger from the strong winds on Thursday and Friday, allowing for thicker slabs. Take the time to investigate the upper snowpack structure, using test slopes and hand pits to see if you have heavy snow over weak snow.

 

AVALANCHE PROBLEM #2i

  • Loose Wet

    Avalanche Problemi
  • Above Treeline
    Near Treeline
    Below Treeline
    Aspect/Elevationi
  • Unlikely
    Possible
    Likely
    Very Likely
    Almost Certain
    Likelihoodi
  • Small (D1)
    Large (D2)
    Very Large (D3)
    Historic (D4-5)
    Sizei
Photo for Loose Wet

Example: Wet Loose Avalanche (1/18/2020)

As temperatures rise on Sunday, even after the possibility of rain ends, expect heavy snow and natural avalanches. If there is more rain, sun exposure, or warming than expected, this cycle will be more widespread. Loose Wet avalanches often start at a point and can entrain lots of snow as they travel downhill, even triggering slabs as they descend. Rollerballs, pinwheels, and fan-shaped avalanche debris are signs that Loose Wet avalanches are possible. Steer around slopes greater than 35 degrees and avoid terrain traps such as creeks, gullies, or cliffs if you notice these signs or witness rain on snow.

 

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.

No Corresponding Mountain Weather Forecast Available