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Archived

Avalanche Forecast

Jan 26th, 2020–Jan 27th, 2020
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Snoqualmie Pass.

More precipitation is on the way to Snoqualmie Pass and expected to thicken any existing slabs at upper elevations on Monday. With a more significant storm impacting the area on Monday night, the possibility exists of increased avalanche danger late in the day if the storm arrives earlier than expected. Take note of changing weather conditions and be sure to have travel plans with plenty of options to avoid avalanche terrain.

Discussion

The Snoqualmie Pass zone went through an impressive avalanche cycle at the tail end of last week after receiving multiple inches of rain. These natural and explosive triggered avalanches were all wet in nature, with Wet Loose, Wet Slab, and Glide avalanches up to size D3. Although less likely moving forward, the snowpack still has lingering potential for glide and wet avalanches as it adjusts to the large volume of water it recently received. Keep an eye out for glide cracks, steep convex rollovers, or unsupported slopes such as cliff bands that did not avalanche during the previous cycle as likely slopes where these wet avalanches may still occur.

Additionally, the large amount of rain received has collapsed many snow bridges and made creek crossing a difficult task in areas of the zone. Take care when traveling around these features.

Snowpack Discussion

Update: January 24th 2020 (The regional synopsis is updated every Thursday @ 6 pm)

During the afternoon of January 23, 2020 one person was buried and killed by an avalanche that released from the roof of a home north of Blewett Pass near Highway 97. The elevation was approximately 1,700ft above sea level. She was found underneath 4 to 5ft of debris. She was discovered and excavated some time after the accident, where CPR was performed. Additional emergency response arrived within 15 minutes, but they were unable to revive her.

Our deepest condolences go out to the family and friends of the victim.

 

January to Remember

A parade of storms since the New Year began brought relentless precipitation, and impressive snowpack growth throughout the region. Areas along the west slopes of the Cascades have rarely gone more than 24-48hrs without precipitation. In the past three weeks, the Volcanoes and Passes received 20-28in of water equivalent, translating into incredible snowfall totals - Mt. Baker Ski Area reported 240in of new snow since January 1. The majority of NWAC weather station sites are reporting snow depths well over 120% of normal for this time of year. Ongoing precipitation and fluctuating snow levels have maintained elevated avalanche danger throughout the month, with avalanche warnings issued for nearly all forecast zones on 4 separate days (January 6, 7, 12, 23).  

Snow depth imagery for the Northwest Region on January 23, 2020. Many areas in the Cascades and Olympics show well over 100 inches of snow on the ground. Image courtesy of NOHRSC Regional Snow Analysis. 

Location

January 1-23 Precipitation (Water Equivalent)

Hurricane Ridge

14.79”

Mt Baker Ski Area

28.65”

Harts Pass

11.2”

Stevens Pass

20.26”

Leavenworth

4.01”

Snoqualmie Pass

25.43”

Paradise, Mt Rainier

24.13”

Mt Hood Meadows

22.34”

Table 1: Precipitation totals for select weather stations January 1-23, 2020. Huge numbers at Baker, Rainier, Hood, and the Passes and there is still another week left this month.

MLK Weekend and a Pattern of Rain on Dry Snow

After a prolonged cold period with arctic air and lowland snow, MLK weekend brought unseasonably warm temperatures and a rapid thaw. High snow levels and rain caused wet avalanche activity throughout the region January 18-19. A few very large natural avalanches occurred at upper elevations where all precipitation fell as snow. A cooling trend followed, creating a pronounced crust that is now buried in almost all forecast zones. Cold, dry snow January 21-22 was followed by a rapid warm-up and the most significant rain on snow event yet, causing avalanche warnings on January 23 for 5 of our 10 forecast zones.

The crown of a very large avalanche around 10,000ft on the Newton Headwall of Mt Hood which likely occurred during the storm late last week. 01/19/20 Photo: Kevin Kayl

The buried MLK crust is widespread throughout the region and a prominent marker in the snowpack. Crystal Backcountry 01/20/20 Photo Jeremy Allyn

One More Week To Go

January isn’t over yet, and the long term forecast continues to show an active and wet weather pattern for the Northwest. The low-snow, drought-like conditions of the early season seem like a distant memory at this point. We’ve certainly made up for lost time in 2020, and this already impressive month looks to end with a bang.

Avalanche Problems

Storm Slabs

With more snow in the forecast, Storm Slabs may be present near and above treeline Monday. Over the weekend, Snoqualmie picked up around 4 inches of snow and built a new surface crust daily. This layering gives plenty of interfaces to investigate as new snow Monday may further thicken any existing slabs. Expect drier and deeper slabs as you ascend in elevation or in areas where winds have deposited new snow on lee slopes the past few days. Use small test slopes and hand pits to investigate the bonding within any new snow along with it's bond to the previous snow surface. Shooting cracks as you travel or blocks of cohesive snow in your hand pits can give you clues about slab potential. If you find a poor bond and more than 6 inches of cohesive snow, avoid slopes greater than 35 degrees. 

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

 

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

 

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1