Avalanche Forecast

On Saturday, several recent avalanches were observed at lower elevations in the Snoqualmie Pass area. Poor visibility and difficult access made observations near and above treeline nearly impossible. Remember, recent avalanches are the simplest sign that you can trigger an avalanche. Glide avalanches were observed on low elevation steep smooth slopes. In these events, the entire snowpack released on water over rock slabs. Glide avalanches are not listed as a problem Sunday but could still occur in very isolated locations. 

Unusual wet avalanches were combined with creek blowouts in several locations. It’s difficult to classify these events, but if you were unlucky enough to be caught by one, the consequences would be severe. Large blocky debris fields were deeply incised with fast-flowing creeks. Some of these avalanches crossed common travel corridors. While more of these unusual slides are not likely Sunday, they have left some truly challenging travel conditions. 

Expect difficult travel at lower elevations with numerous open creeks, punchy snow, and a variety of obstacles including bare ground. Simply moving over the snow at lower elevations may be the most dangerous part of your day. 

One of several unusual wet avalanche/creek blowouts in the Alpental Valley. The creek channel is 3-6ft deep and difficult to cross safely. Photo: Dallas Glass

December 19th, 2019 (The regional synopsis is updated every Thursday @ 6 pm)

Let’s take a moment to recap what happened over the past week:

A potent winter storm arrived on the 12th, adding to the very shallow snowpack throughout the region. Anywhere from 6-36” of snow fell between the 11th and 15th. Places like Mt Baker, Paradise, Mt Hood, and White Pass were the winners regarding snowfall, with quite a bit less for areas further east of the crest like Mission Ridge, Blewett Pass, and Washington Pass. 

The most notable avalanche activity occurred in the Mt. Baker backcountry where numerous human triggered storm slab avalanches occurred (with several big enough to injure, bury, or kill a person). The majority of these occurred on upper elevation, north and east facing terrain. Besides the danger posed by the size of the avalanche, many slides quickly revealed rocks and other obstacles barely hidden below the snow surface. 

The storm layer took time bond with the underlying snow surface, and we saw the likelihood of triggering slab avalanches slowly decrease over a handful of days. The avalanche danger was at Considerable for many places on Saturday the 14th, then tapered to Moderate on Sunday, and eventually reached Low in many places by Tuesday and Wednesday. 

A large, human triggered avalanche on the old snow interface. East aspect of Table Mountain (West-North Zone) at 5,500ft. December 15,2019. Photo by Brooks Broom. 

Backcountry travelers have noted generally thin and shallow snowpacks, with a range of structures across the region. Many folks were skeptical of the layering they found. People were able to dig down and observe weak layers in many areas. These were buried in late November and early December. In some places they presented as weak snow over a crust, in others, a layer of feather-like surface hoar. Cold temperatures have likely preserved many of these layers, and will be worth considering as the snow piles up.

Below is a list of commonly visited locations and their snowpack depths in inches (as of December 19th at 4am). Check the weather station hourly data feed and watch as the subtropical javelin of moisture (also known as a strong atmospheric river) changes conditions dramatically over the next few days. 

Total Snow Depth in Inches as of December 19th at 04:00 AM.

-Matt Primomo