ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday February 9th, 2019
Posted by Aleph Johnston-Bloom on 02/09/19 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 be large enough to bury, injure or kill a person.  Identify high consequence terrain and practice safe travel protocols.  Give cornices a wide berth, limit travel under glide cracks and watch your sluff.

SUMMIT LAKE / JOHNSON PASS:  Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present  including the MLK buried surface hoar. Human triggered slab avalanches 1-3′ thick remain possible. Choose terrain wisely.

LOST LAKE / SEWARD:  Thursday we received a report of a human triggered avalanche where someone was caught, carried and injured on the Harding Icefield trail. This avalanche occurred last Saturday, February 2nd. Seward and Lost Lake received new snow and winds over the past weekend. This area has very little snowpack info and extra caution is advised.  

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.

Special Announcements

Heading to Hatcher Pass? GET the forecast! Check out  the Hatcher Pass Avalanche Center Saturday Advisory click  HERE.

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

The MLK buried surface hoar roughly 1-3′ deep has been responsible for 13 human triggered avalanches over the past two weeks. The last one was three days ago on Eddies On that day snowpack tests were pointing toward a stabilizing weak layer and then the 2′-3′ deep avalanche was triggered remotely from the ridge on a steep, unsupported slope. This avalanche illustrates that snow pit tests are unreliable for the current problem. Furthermore, no signs of instability have been seen in conjunction with several of the 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 slope before it avalanches and slabs have been often triggered remotely from ridgelines. There are also many slopes that could in fact be stable, but unfortunately this problem is still a guilty until proven innocent situation.

What to keep in mind today:
   1-  This weak layer is widespread in the region and seems to be particularly suspect between 2000′-2500′ due to a melt-freeze crust associated with it. 
   2-  Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones 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. Steep, connected, unsupported slopes are the most suspect!

Eddies remote triggered avalanche, 2-6-19.

 The MLK buried surface hoar layer was easy to spot in a pit on Seattle Ridge, 2-7-19. 

Avalanche Problem 2
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
  • TYPE
    Cornice

CORNICES: Last weekend there was a large cornice fall triggered in upper Seattle Creek drainage. Cornices are looming large in some of the Alpine terrain. Give them an extra wide berth as they often break farther back than expected.

LOOSE SNOW AVALANCHES (dry and wet): Dry loose “sluffing” is possible in steep terrain. Daily warming and radiation from the sun could warm surface snow on steep Southerly aspects. Watch for roller balls and small wet-loose avalanches especially under rocky areas. 

Corniced ridge and loose snow avalanches on Magnum back towards Super Bowl, 2-8-19.

 

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.

Glide cracks below PMS Bowl on Magnum, 2-8-19.

 

Mountain Weather

Yesterday:  Skies were partly to mostly cloudy with high overcast clouds. Winds were light and westerly and temperatures were in the 20Fs. No precipitation. Overnight temperatures dropped a little and winds remained light.  

Today:  Mostly cloudy skies and light winds. Temperatures will be in the 20Fs to low 30Fs. No precipitation forecast. Overnight easterly winds will bump up with gusts into the 20s.    

Tomorrow:  Mostly cloudy skies and snow showers throughout the day as a trough moves in from the west. Temperatures will be in the 20Fs and winds will be easterly 10-20 mph with gusts into the 30s.  Monday looks to have a period of clearing before the next chance of snow Tuesday.  

*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′)  20      0      0     25  
Alyeska Mid (1700′)  29     0    0      51    

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  26  W  3 18  
Seattle Ridge (2400′)  29  *N/A *N/A   *N/A