ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday March 30th, 2019
Posted by Wendy Wagner on 03/30/19 at 7:00 am.
The Bottom Line
Considerable Avalanche Danger
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

The avalanche danger is LOW below 3,000′ this morning and will rise to CONSIDERABLE this afternoon/evening with the heat of the day. Once surface crusts soften and become unsupportable, human triggered wet loose avalanches will be likely on steep sunny slopes. These could be large and dangerous in big terrain and could initiate a wet slab avalanche, creating a much larger slide. Cornice falls are also likely late in the day and glide avalanches possible at anytime. Above 3,000′ where the snow is drier, a MODERATE  danger exists for triggering a deep slab avalanche on all aspects.  

PORTAGE VALLEY:   Summer trails with avalanche terrain overhead, like Byron Glacier Trail and Crow Pass, are not recommended in the afternoon or evening due to the possibility of an avalanche occurring above.  

SUMMIT LAKE (& INTERIOR EASTERN KENAI MTS):   Human triggered slab avalanches remain possible in upper elevation terrain on all aspects. This area has a thin  snowpack with many weak layers. High elevation sun-baked slopes are the most suspect for triggering a slab.  

SEWARD/LOST LAKE:   The snowpack is warming up and dangerous avalanche conditions are occurring late in the day in this area as well. A large avalanche released on Mt. Marathon Thursday. These types of avalanches remain possible.

3. Considerable
Alpine
/ Above 2,500'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
3. Considerable
Treeline
/ 1,000'-2,500'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
2. Moderate
Below Treeline
/ Below 1,000'
Avalanche risk
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Special Announcements

  • Headed to Hatcher Pass? Be sure to check out HPAC’s Saturday’s forecast!!  
  • The Friends of the Chugach National Forest Avalanche Center is an  official Pick. Click. Give. organization.  When you apply for your PFD please consider supporting your public avalanche center. We rely heavily on your contributions, which provides not only weather stations and daily forecasts but a host of other public avalanche services. Thank you to all of our donors past, present and future!
Avalanche Problem 1
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

As they say, timing is everything. Yes, it is still March for a couple more days…but the snowpack has been forced into a springtime transition, similar to what is typically seen in late April. Cool mornings with a frozen snow surface below 3,000′ harbors a low avalanche danger. By noon the day is heating up and crusts are softening on East aspects, 1-3pm South aspects and 3-5pm on West aspects. Once the crusts melt away and your boot easily sinks into mushy wet snow, your stay is overdue and it’s time to get onto shaded slopes or off the one you are on and well away from runouts. 

Wet loose and even wet slabs are likely to be triggered by people once the snow surface becomes soft and unsupportable. This was seen yesterday on Seattle Ridge. Check out the photos below. These slides can be small and easily escaped. They can also turn into large, destructive and unmanageable avalanches. The larger the terrain the more likely a small wet avalanche can grow into a large and scary one. These types of avalanches can be easily avoided if sticking to slopes that are still cool with a supportable crust or on shaded northerly aspects. 

 Seattle Ridge Up-Track: Heads up late in the day! 

    

Thank you to Sean Fallon (left photo) and Troy Tempel (right photo) for sending in these images of the Seattle Ridge motorized up-track. This ‘small-ish’ avalanche was triggered yesterday by a snowmachiner while descending through the trees above the uptrack. The rider was able to sidehill off the slab and was not caught. The debris entrained additional snow as it ran downslope, gaining momentum, and crossed the up-track.

 

Avalanche Problem 2
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
  • TYPE
    Deep Persistent Slabs
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

In the upper elevations, above 3000’, mostly dry snow exists. Southerly aspects are seeing the effects of the sun and sport a sun crust in the morning that is typically softening later in the day. Under the 5-10 feet of settled storm snow, from the mid-March stormy weather, sits a somewhat questionable old layer of facets/buried surface hoar and crusts. Many avalanches released on this layer during the storms, yet only a few avalanches have been seen since skies cleared – and these have been large. The last slab we know of was in Summit Lake on Butch Mtn. This was most likely triggered naturally, possibly by a cornice fall, we believe on Tuesday night or Wednesday (March 25/26). Although in dry upper elevation snow, the slope was being impacted by direct sunshine and warm temperatures; a contributing factor. 

If headed out for a long day in the hills, keep in mind deeper weak layers could be lurking and sunlit slopes are the most suspect. Some good rules of thumb are:

  • Identify and avoid cornices and dangerous terrain traps (large triggers such as a cornice fall could pull out a deep slab)
  • Avoid steep solar aspects that are heating up later in the day
  • Use safe travel protocols like traveling one at a time from established safe zones

 

For anyone that missed this photo yesterday. This is the natural slab avalanche on Westerly facing Butch Mt in Summit Lake. 

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

Don’t underestimate the glide avalanche problem! Many glide cracks have avalanched over the last few days. The Southeast face of Seattle Ridge looks like a war zone with several trademark brown streaks left from glide avalanches. Remember, glides are very unpredictable and fail at the ground pulling out the entire season’s snowpack. Many cracks are opening up in popular terrain and avoiding/limiting exposure under these is strongly recommended. 

Glide avalanche in Lynx Creek, released yesterday (Mar 28). Note how destructive even a small glide avalanche can be. The initial debris gouged to the ground on the descent, picked up more of snowpack in its the path, and sent the total debris far down the slope into low angle terrain.

Mountain Weather

Yesterday:    Sunny skies were over the area once again. A few convective clouds did develop due to moister air moving through along with the evaporation of the snowpack. Temperatures hit the mid 40’sF at the mid and lower elevations, while slopes above 3,000′ saw temperatures remain just under 30F. Ridgetop winds have been light and variable.  

Today:   Mostly sunny skies are forecast with a chance for some low clouds this morning before burning off this afternoon. Temperatures should climb from ~30F into the mid 40’sF in the mid and lower elevations with high elevations reaching 30F. A light Northerly breeze is expected along ridgetops (~5mph).  

Tomorrow:    Sunny skies and warmer air aloft looks to stream in tomorrow, pushing temperatures along 4-5,000′ ridgelines into the low 30’s F. Ridgetop winds are expected to remain light and variable. Weather models are pointing to a breakdown in the ridge of high pressure entrenched over Southcentral Thursday. Until then, sunny skies, warm temps and light winds should persist. Stay tuned!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37   0   0   68  
Summit Lake (1400′) 36   0   0   22  
Alyeska Mid (1700′) 37   0   0   62  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   W   4   10  
Seattle Ridge (2400′) 33   variable   2   6