ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Friday February 8th, 2019
Posted by Wendy Wagner on 02/08/19 at 7:00 am.
Avalanche risk
The Bottom Line
Moderate Avalanche Danger
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

The avalanche danger is  MODERATE. Triggering a large slab avalanche 2-3′ thick remains possible on steep slopes above 2,000′. These slabs can be triggered remotely from ridgelines and large enough to bury, injure or kill a person. In addition, watch for wet sluffs on steep sunlit slopes. Give cornices a wide berth and limit travel under glide cracks. Identify high consequence terrain and practice safe travel protocols. A lot of uncertainty exists in our current snowpack.

SUMMIT LAKE / JOHNSON PASS:  A variety of weak layers exist in the snowpack and human triggered slab avalanches 1-3′ thick remain possible. Choose terrain wisely.

LOST LAKE / SEWARD:  We received a report of a human triggered avalanche yesterday, which occurred on last Saturday on Exit Glacier trail. New snow and winds over the weekend have elevated the avalanche danger near Seward and Lost Lake. This area has very little snowpack info and extra caution and conservative decision making is necessary.

2. Moderate
Alpine
/ Above 2,500'
Avalanche risk
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2. Moderate
Treeline
/ 1,000'-2,500'
Avalanche risk
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1. Low
Below Treeline
/ Below 1,000'
Avalanche risk
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Avalanche Problem 1
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
  • TYPE
    Persistent Slabs
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

 “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.

 

Avalanche Problem 2
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
  • TYPE
    Wet Loose
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

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. 

Additional Concern
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
  • TYPE
    Glide Avalanches

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.

Mountain Weather

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.

PRECIPITATION 24-hour data (6am – 6am)

  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  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25    E 4   17  
Seattle Ridge (2400′) 27   *N/A   *N/A     *N/A