The Bottom Line: A blustery storm is creating dangerous avalanche conditions. The most dangerous slopes are near and above treeline where you can trigger large avalanches that could break above and around you. You can avoid triggering avalanches by staying off thickly-pillowed, wind loaded slopes and steering well-around wind sculpted features on slopes 35 degrees and steeper.
Snow and Avalanche Discussion
Light, dry snow snow fell Sunday night through Tuesday with gusty winds. Expect a mix of snow and freezing rain with more wind to maintain avalanche conditions on Wednesday. In the past two days at Stevens Pass, observers have reported skier triggered avalanches in wind-loaded terrain, even below treeline. Close to 1.5 feet of snow has accumulated since Sunday with wind drifts forming in open terrain. There's uncertainty about how well the wind and precipitation forecast will verify. Carefully observe new snow amounts and drifts on Wednesday.
Regional Synopsis
January 7, 2019
This latest round of storms in early January continues to highlight some of this season’s region-wide themes in our snowpack. I’d describe them as Bottom to Top, North to South, and East to West. Let’s take a look at each of these.
Bottom to Top: In general this winter has been on the warm side in the Cascades. No where is that more evident than in the lack of low elevation snow. Heavy rain events continue to wash-away and thoroughly wet the lower elevation snowpack. In most regions you will see substantial increase is the height of snow from low elevations (3000 ft), to mid elevations (4500 ft), and again at upper elevations (5500/6000 ft). Above the typical rain lines (5000-6000 ft) a deep and cold mid-winter snowpack exists.
Jan 5, 2019: The dark timber in the Coast Range highlights the thin snowpack at lower elevations and the deeper winter-like snowpacks near and above treeline: Photo: Simon Trautman
North to South: With few exceptions, this season’s storm tracks have favored the North Cascades. Sunday, Mt Baker’s Heather Meadows weather station passed 100 inches of snow on the ground. A quick look around the state’s weather stations demonstrates just how deep this snowpack is. Most other locations are reporting between 50 and 75 inches. The massive amounts of snow for the northern forecast zones are reflected in several impressive avalanche cycles spread out over the last month.
NWAC weather station graph of the height of snow on the ground. Mt Baker passed the 100 inch mark Sunday.
East to West: Several stacked persistent weak layers have been buried in the eastern forecast zones. This isn’t unusual, but it is noteworthy. The thickness of the slabs over these weak layers can vary greatly. Closer to the Cascade Crest, the deep snowpack may more closely resemble Stevens or Snoqualmie Passes. Further east, shallower snowpacks, and significant variability are keeping snowpack assessment tricky.
Canadian sized surface hoar found buried by 18†of snow in Icicle Creek above Leavenworth on December 31st: Photo by Matt Primomo.
So what now? Well, on January 3 and 4 a high elevation rain event impacted areas from Mt Baker to Mt Hood. In many locations this has created a firm and thickening crust. In these locations, this new crust is limiting the impacts of any deeper weak layers. In locations that didn’t receive as much rain like WA Pass, Mission Ridge, Crystal Mt, and White Pass, how the small amount of rain impacted the mid and lower snowpacks remain to be seen.
Rain and rime crust at 6,500ft above Gallagher Head Lake in the East Central Zone, Jan 5th. This layer was 3 inches thick in this location. Matt Primomo photo.
One thing is for sure, we’re not even a month into the winter season, there’s a lot more winter to come.
Avalanche Problems
Wind Slabs
While you can trigger wind slab avalanches at all elevations, they could be big enough to bury or kill you near and above treeline. You’re most likely to trigger avalanches on slopes that are steeper than 35 degrees on the leeward (down wind) side of ridges. The combination of cold temperatures, light snow, and gusty wind has drifted snow very efficiently and into unique areas. Expect wind drifts in open areas below treeline, and cross-loading on slopes well below ridges. Drifting has occurred from both westerly and easterly winds this week. Take note of how the distribution of wind slabs will change as you move through terrain.
Watch for signs that you can trigger a wind slab avalanche, such as; Actively blowing snow, cornices hanging over a slope at the top of a ridge, wind sculpted features or thick lens-like pillows, especially smooth snow cover, and deeper snow compared to the opposite side of the ridge. The best way to manage the risk of being caught in a wind slab avalanches is to:
Avoid leeward, wind-loaded start zones and cross-loaded features low on slopes
Steer around wind features as well as convexities, where slopes roll steeper
Stop and re-group in safer areas, well out from under and away from wind-loaded avalanche terrain.
