ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday February 23rd, 2019
Posted by Wendy Wagner on 02/23/19 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.

There is a  MODERATE  avalanche danger on slopes above 1,000′. Triggering a wind slab avalanche around a foot thick is possible on wind loaded steeper slopes. Additionally, sunshine and warm temperatures may cause wet sluffs in steep southerly facing terrain. As always, give cornices a wide berth and limit exposure under glide cracks.

GIRDWOOD / PORTAGE / PLACER:   Wind slabs could be deeper, up to 2′ thick, due to more snow that fell last week.  

SUMMIT LAKE / JOHNSON PASS:    A shallow snowpack with various weak layers exist. Triggering a larger, more dangerous slab remains a concern. Conservative terrain choices and a cautious mindset is advised.

SEWARD / LOST LAKE:   Recent snowfall and strong northwest winds impacted this region as well. Watch for and be suspect of wind loaded slopes. Triggering a deeper more dangerous avalanche is uncertain due to limited snowpack information.

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!
  • Join us in getting snow depth data for the Community Snow Observations crew!! Website is communitysnowobs.org. It’s easy to do, you just need a smart phone and 30 seconds.  

Avalanche Problem 1
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
  • TYPE
    Wind Slabs
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

With a sunny and springlike weekend upon us, triggering a lingering wind slab is our main concern. Last Thursday’s impressive outflow event loaded predominantly south and easterly aspects as the northwest winds hammered the mountains. We can expect wind slabs to be generally hard, stubborn and around a foot thick. The problem is that some slabs are sitting on weak faceted older snow, which is keeping them from bonding quickly. Furthermore, warming over the next several days can do funny things in the snowpack and cause slabs to be more touchy.

All this said, keep a close eye out for recent avalanches, whumpfing and cracking in the snow. Many slopes have variable wind effect with loaded areas and scoured areas. Watch for rounded and pillow like features as these are the windloaded areas that could slide. 

SUN EFFECT:  The days are longer and the sun is higher. Although the snow surface has seen a good degree of wind damage, southerly facing slopes may be soft and susceptible enough to product wet sluffs. There are three things acting in sync over the next several days to cause warming, 1) direct sun, 2) calm winds and 3) warm ambient temperatures. Watch for the snow to start to become moist or wet and remember even a small moist of wet sluff in steep rocky terrain can become unmanageable. 

 

Snow pit from Seattle Ridge’s slide path Repeat Offender that sits just to the south of the motorized up-track.

 

 

Video is from Thursday (outflow event day) in the Skookum drainage. Video linked HERE

Avalanche Problem 2
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

South of Turnagain Pass in the Summit Lake and Johnson Pass area, a thinner and weaker snowpack exists. Various weak layers of facets and buried surface hoar reside in the middle and base of the pack. The strong NW winds Thursday proved these buried weak layers are still a concern as many natural avalanches were seen and many of these stepped down into the deeper weak layers. Moving forward, it’s good to be very suspect of these regions with a thin snowpack. Avoiding wind loaded steep slopes and large terrain is prudent as not only a wind slab, but a larger slab may be triggered.

As a reminder for all areas, including Turnagain Pass, there is an older weak layer we are continuing to track. This is the MLK Jr buried surface hoar 1.5’-3’ below the surface. It’s good to keep in mind this layer remains as well as the various layers of facets and crusts in the thinner snowpack zones. Keeping up on our safe travel protocol, including exposing one person at a time and watching our partners is key. 

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

New glide cracks are opening up around our region. The last known release was on the south side of Goat mountain in Girdwood Valley on Tuesday. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks. A short list of known cracks in popular zones:  Magnum, Lipps, Seattle Ridge, Eddies, Lynx Ck. Keep your eyes out for these! 

 

 

   

Magnum glide crack that has been slowly opening for over a month now. It is unknow whether this crack will release or not, it’s always best to hedge our bets and limit exposure under this and any other crack. (photo: Duncan Wright)

Mountain Weather

Yesterday:   Sunny skies were over the region with light and variable winds along ridgetops. Daytime temperatures were near 30F at sea level and near 20F along ridgetops. Overnight an impressive inversion has set up. At sea level and in valley bottoms temperatures have dropped to the single digits, while ridgetop temperatures continue a slow rise into the 20’sF.  

Today:   Another round of sun with light and variable ridgetop winds are on tap. Temperatures should recover into the teens in valley bottoms before cooling back down tonight. Upper elevation temperatures should continue a slow rise into the mid 20’sF.  

Tomorrow:    A ridge of high pressure has built over Southcentral is entrenching itself for the foreseeable future. We can expect sunny skies with gradually warming temperatures for the next 5 days or more. We could see very springlike conditions at mid to upper elevations as temperatures climb to 30F by Monday.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 20   0   0   62  
Summit Lake (1400′) 12   0   0   30  
Alyeska Mid (1700′) 18   0   0   57  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17   Variable   6   18  
Seattle Ridge (2400′) 20   Variable   3   9