Avalanche Forecast

Rain likely reached at least 6000’ for much of the zone last week and left a firm crust in many locations. Above this elevation, previously formed wind slabs are unlikely to trigger but use caution on steep slopes with wind drifted snow. Steer around steep convex slopes below cornices and when you find pillow-like snowdrifts.

Shooting cracks are a sure sign you could trigger an avalanche in terrain steeper than 35 degrees. Photo: Heiko S.

Also at elevations higher without a prominent and firm crust, persistent weak layers may still be sensitive to human triggering. 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 can be triggered remotely or from low angled slopes.

At low and mid elevations, exposed or shallowly buried ground hazards, like rocks, stumps, and creeks can amplify the consequences of even a small avalanche.

If you’re out testing new holiday gear remember to submit an observation! The easiest way is to post a photo of avalanches or general conditions. 

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 26, 2019 (The regional synopsis is updated every Thursday @ 6 pm)

No matter where you are in the northwest, the snowpack looks a world different than it did a week ago. A major storm, widespread avalanches, developing weak layers, and an initially thin snowpack made for a hectic week. Let’s take a look at a few large scale trends for our holiday season. 

A very large natural avalanche (D3) on the Shuksan Arm near Mt Baker that occurred during the storm cycle. Photo: Adam U. 

Wet and Wild

“Some of the highest precipitation rates I’ve ever seen.” “Absolutely puking!” “Rivers running in the streets.” “Snowing snow hard I can’t see my hand in front of my face.” These were all statements we heard describing the wet and wild storm that impacted the Northwest from about Thursday (12/19) through Sunday night (12/22). Water totals were staggering in many locations (Table 1). For Hurricane Ridge, Mt Baker, Washington Pass, and high elevation terrain this deluge translated into significant snowfall. However, warm air in the central and southern parts of the region brought rain well into the near treeline bands. Whether your favorite spot saw rain or snow, four things are clear. 1. This was a huge loading event. 2. A widespread natural and triggered avalanche cycle (up to D3) occurred. 3. Avalanche danger spiked during and just after the storm before trending down through the week. 4. The snowpack changed dramatically. 

Location

Precipitation 12/19-22

Hurricane Ridge

4.97”

Mt Baker Ski Area

7.35”

Washington Pass

3.53”

Stevens Pass

6.28”

Leavenworth

2.94”

Snoqualmie Pass

7.89”

Crystal Mt Ski Area

7.45”

Paradise, Mt Rainier

6.57”

Mt Hood Meadows

2.18”

Table 1: Precipitation totals for select weather station locations December 19-22.   

The Emergence of Persistent Slab Avalanche Problems

Coming out of this huge loading event, there was hope that many of the early season weak layers had been destroyed. Unfortunately, this was not the case in some locations. Old weak snow layers reared their heads in areas east of the Cascade Crest and near Crystal Mountain. While the exact extent and character of these layers can differ slightly, most locations are finding a layer of weak sugary facets associated with a crust about a foot above the ground. Persistent slabs are tricky to assess. Do not solely rely on snowpits and snowpack tests to help you choose terrain. How will these layers change going forward? Only time and observations will tell. 

You may find weak sugary facets near a crust about 12 inches above the ground similar to what you see here. Photo: Jesse Charles

Low Tide Snowpacks During the Holidays

The storm this past week definitely helped the meager early-season snowpacks in all locations. Areas like Hurricane Ridge, Mt Baker, and Washington Pass experienced a jump of 20 or more inches in their snow depths over the past week. However, even with these increases, an early season snowpack still describes most locations. Expect numerous obstacles as you travel including open creeks, rocks, and trees. With this thin snowpack, limited access, and difficult travel we still have limited observations in some regions. 

Open, deeply incised creeks in the Alpental Valley. Photo: Dallas Glass

Lack of information leads to a higher than normal degree of uncertainty. If you travel to higher elevations or more remote trailheads, recognize you could experience different conditions than the forecast suggested. You can help us fill in the gaps by submitting your observation here. 

Happy Holidays! 

-Dallas Glass