“It’s a lot easier when the snowpack is predictably unstable rather than unpredictably unstable”. That is the quote of the night from a 5th Annual Snowball attendee; A BIG THANKS to all those that sold-out the 49th State Brewing Co. for our mid-season fundraiser last night!!
What that quote is conveying is our snowpack is not giving us signs a slope may be unstable until it is too late, it is unpredictable. Under the excellent soft surface snow is a layer of buried surface hoar, roughly 1-3′ deep, that has been responsible for 13 human triggered avalanches over the past two weeks. Heather’s experience two days ago on Eddies is a perfect example. Snowpack tests were pointing toward a stabilizing weak layer then moments later boom, she and her partner ski away from the pit on the ridge and remote trigger a 2′ thick slab (photo below). This is telling us that snow pit tests are unreliable for the current problem. Furthermore, no signs of instability have been seen in conjunction with several other large human triggered avalanches on this layer.
This is a tricky situation if wanting to get on slopes over 35 degrees and have a safe day. Several tracks may be on a slopes before it avalanches and slabs have been often triggered remotely from ridgelines. There are also many slopes that could in fact be stable, but this problem is guilty until proven innocent. What can we do?
1- Keep in mind this weak layer is widespread in the region.
2- Use safe travel protocol. Expose one person at a time, watch our partners and be rescue ready.
3- Consider the consequences of an avalanche. Will the debris pile up deeply in a terrain trap or strain a person over cliffs and rocky terrain? Slopes with a fanning runout, spreading the debris, are more favorable for a positive outcome in the event of an avalanche.
4- As always, one can simply stick to slopes under 35 degrees with nothing steeper above to avoid the issue.
Slab avalanche triggered remotely from the ridge on Eddies southwest face. This slide was 2′ thick and debris piled up in a terrain trap (gully) below. Note the glide crack on the right flank of the slide as well.
Snow pit near the top of the Repeat Offender slide path, just to the south of the motorized up-track along Seattle Ridge. The weak layer is easily seen in the pit wall.
South of Turnagain – Johnson Pass/Summit Lake zone: Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present, including the MLK buried surface hoar. This area also received additional snow on Sunday and Monday and elevated Easterly winds. Similar to Turnagain Pass an avalanche triggered in this zones could propagate an entire slope and be large enough to bury or kill a person.
Sunny skies, light wind and warm temperatures may heat the snow surface enough on southerly facing steep slopes to initiate wet/moist sluffs. It’s that time of year the sun can have an effect. Dry sluffs in steep terrain should be expected on steep shaded slopes.
Glide cracks are moving and opening across the region again. The last glide crack to release into an avalanche was roughly a week ago in the Summit zone just north of Manitoba. Look out for glide cracks and limit exposure under them.
Yesterday: Mostly sunny skies with a few high clouds were over the region. Ridgetop winds were light from the east (5-10mph). Temperatures have been holding steady in the mid 20’sF along ridgelines and near 30F at 1,000′.
Today: Another nice day is on tap with mostly sunny skies. Temperatures should remain near 30F at 1,000′ and in the mid 20’sF along ridgelines. Ridgetop winds are expected to also remain light, yet from a southwesterly direction, in the 5-10mph range.
Tomorrow: There is a good chance the high-pressure ridge over us currently will stay for most of Saturday, keeping skies mostly clear and winds light. Clouds associated with the next weather system look to move in on Saturday night with a chance for precipitation on Sunday. Stay tuned.
*The Seattle Ridge anemometer (wind sensor) was destroyed. We have a replacement on the way and it should be operational by mid February.
|Temp Avg (F)||Snow (in)||Water (in)||Snow Depth (in)|
|Center Ridge (1880′)||30||0||0||58|
|Summit Lake (1400′)||23||0||0||26|
|Alyeska Mid (1700′)||30||0||0||52|
|Temp Avg (F)||Wind Dir||Wind Avg (mph)||Wind Gust (mph)|
|Seattle Ridge (2400′)||27||*N/A||*N/A||*N/A|