Avalanche Forecast

We received a public observation of a snowmobile triggered slab avalanche SE of Darland Mt on a NE aspect around 6600’ (photo below). The avalanche was triggered on Saturday afternoon. No one was buried or injured. Snow depths averaged around 4 ft. in this area.

Recent storm snow instabilities at upper elevations should be healing over time with the avalanche danger trending down overall. However, persistent weak layers may continue to be a problem well after the storm. Without more direct evidence, you’ll have to tread carefully in terrain connected to slopes steep enough to slide. Persistent slab avalanches can break in surprising ways and from lower angled slopes. 

This observation also helps us paint a picture of the rain/snow-line following the recent atmospheric river event. Rain likely reached at least 6000’ for much of the zone with remote weather stations showing a decrease in total snow depths due to a sustained period of rain and above freezing temperatures on the back end of the multi-day event. 

Keep in mind that exposed or shallowly buried ground hazards, like rocks, stumps, and creeks can amplify the consequences of even a small avalanche.

If you travel to the East South backcountry, please submit an observation.

Forecast Schedule and No Rating definition

At this time, we do not have enough specific snowpack information to issue an avalanche hazard rating for the East South zone. However, even when No Rating is applied, applicable avalanche conditions and backcountry travel advice will be provided throughout the season. When weather systems produce very dangerous avalanche conditions in adjacent zones, NWAC will issue an avalanche warning for this zone as well.

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