The Bottom Line: Recent strong winds at Stevens Pass formed slabs in a variety of unusual locations including well below ridgeline. You can travel safely by avoiding open slopes greater than 35 degrees in areas were you see or feel signs of wind transported snow. Fresh cornices, the snow blown out of the trees, and firm hollow snow under you can all be signs that wind slabs are likely nearby.
Snowpack and Avalanche Discussion
This is a tricky weather forecast, and since the weather is driving the avalanche danger, we have a higher level of uncertainty. The weather models are struggling to determine the freezing levels, and how much new precipitation will fall Wednesday night into Thursday morning. Keep your eyes open. If you see observations that don’t line up with the weather or avalanche forecast, stop and reevaluate. We are confident the avalanche danger will slowly decrease as this weather system exits the region and unstable snow has time to gain strength.
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
You will need to use your eyes and sense of touch to locate wind transported snow as you travel. Look for signs like blowing snow, fresh cornices, and the snow blown out of trees. Feel the snow under you as you travel. Does it feel more firm in one location than another? Does it seem hollow? If you see or feel any of these observations, wind slabs may be nearby. Recent winds formed slabs in some unusual locations like well below ridgelines, on the sides of gullies, and in places that are normally scoured. You can stay safe by traveling on ridges, scoured areas, and any slope less than 35 degrees.
