Avalanche Forecast

On Saturday, two snowboarders triggered a slide at Stevens Pass off Cowboy Mountain. They were partially buried, and self rescued. See the accidents page for more details. 

Though quite a distance away, the weak layer is similar to what has been observed in some areas of the Northeast Cascades. On Sunday, an observer near Powder Cache found a layer of buried surface hoar about a foot below the surface on shaded aspects. This was within the storm layers. Professional guides reported two small (D1) ski triggered avalanches from Sunday on a northerly aspect at 5,400ft, failing within the storm layers about a foot down. Facets over a crust on southerly aspects have been observed.The last loading event was on the 12th and 13th, which created natural avalanches with the widest propagation occurred on east and southerly aspects in the area. Quite a bit of uncertainty remains and it appears that lots of variation can be expected between Washington Pass and areas further east. The commonality is that observers continue to find more than one different faceted layer to be concerned about. 

In places further east such as Goat Mountain and Twisp River, the danger may be closer to Considerable below treeline. Facets over a crust are the culprit.

February 15, 2019

Since February 8th, the mountains (and low elevation cities) of the Pacific Northwest have experience cold and very storm weather. Significant snowfall has added up in all forecast zones. Records from Snoqualmie Pass DOT avalanche workers back to 1973 show that February 11-12th set a record for the most snow recorded in a 24hr period at that location. The table below shows storm totals starting February 8th through the morning of the 13th

5 day totals ending morning of Feb 13th

Water Equivalent (inches)

24hr storm totals

(inches)

Difference in Height of Snow (inches)

Hurricane Ridge

1.97

N/A

+ 30

Mt. Baker

1.94

44

Washington Pass

1.66

NA

+ 16

Stevens Pass

2.71

49

Snoqualmie Pass

3.91

80

Mission Ridge

1.86

38

Crystal

2.91

59

Paradise

4.55

N/A

White Pass

N/A

57 (4400ft)

+ 26 (5800ft)

Mt. Hood Meadows

4.70

43

Heavy precipitation brought many mountain regions to their tipping point. Avalanches ran readily with a peak of snowfall intensity. For Stevens Pass, Snoqualmie Pass, East Central, West South, Mt Hood, and possibly West Central zones we have good confirmation that this cycle happened from the night of February 11th through the 12th. In other zones, snow totals haven’t been significant enough for widespread avalanche cycles, or we lack data (like in the East South zone).

A natural persistent slab avalanche (D2.5) on a southeast aspect at 6,600ft. Grindstone Mtn in Icicle Canyon. Likely ran 2/12. Photo: Matt Primomo

The high rates of precipitation drove avalanches in the storm snow. Notably, a persistent weak layer of facets and surface hoar was buried in most zones on February 8th. Storms produced a widespread and prolonged cycle of avalanches on the February 8th interface, involving a variety of aspects and elevations. Local ski patrols, highway workers, and backcountry travelers reported extensive avalanching with widely propagating crowns and very sensitive conditions. With less stormy weather, observers have just begun to get a sense of the extent of the avalanche activity. Triggering persistent slab avalanches will be a concern for backcountry travelers in zones where the February 8th weak layer is active for at least the near, if not distant future. Stay tuned for more updates.

Large surface hoar near Snow Lake Divide on February 7, 2019 just before it was buried on the 8th. Photo: Jeremy Allyn