ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Wednesday March 27th, 2019
Posted by Aleph Johnston-Bloom on 03/27/19 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  MODERATE  across the Advisory area this morning but will rise to CONSIDERABLE in the Alpine later in the day and natural deep slab and wet loose avalanches will become possible. With warm temperatures and direct sunshine on steep, solar aspects triggering a large, dangerous slab avalanche in the Alpine is also still a concern.  Choose terrain carefully.  Give cornices and glide cracks a wide berth. Pay attention to changing surface conditions and avoid solar aspects later in the day.  

PORTAGE VALLEY – Byron Glacier trail.    There is a still a chance that direct sunshine and afternoon warming could initiate wet loose avalanches that run to lower elevations or loosen cornices above this terrain. Hiking the summer trail is not recommended.  

SUMMIT LAKE (& INTERIOR EASTERN KENAI MTS):   The snowpack in this zone is shallow and has many weak layers, with the direct sunshine and warm temperatures  human triggered slab avalanches remain possible in upper elevation terrain. In addition, look for wet loose avalanches and changing surface conditions in the afternoon.  

SEWARD/LOST LAKE:  Similar to Turnagain –   Human triggered avalanches will be possible will today with warm temperatures and direct sunshine. Extra caution especially on steep, solar aspects in the Alpine is recommended.

3. Considerable
Alpine
/ Above 2,500'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
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.
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.

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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

Small wet loose avalanches were observed yesterday and remain a concern today as temperatures remain unseasonably warm and the sun shines on the snow. It will be crucial today to pay attention to changing conditions and adjust travel to avoid hazard. Springtime travel in avalanche terrain is generally safer in the morning when the slopes are more frozen. If heading out note that the temperatures overnight were higher than the past two nights especially in the mid-elevation band and there may be a longer stretch of above freezing temperatures today. The Alpine may see some of the highest temperatures yet. Increasing cloud cover is in the forecast for the day and has the potential to trap more heat and “greenhouse” the snow. Pay attention to crust supportability, if you are sinking in on your skis or trenching on your machine or dropping in with your boots it’s a good idea to get off the slope. In the Alpine drier snow may feel like mashed potatoes as it heats up. Look for roller balls and push-a-lanche conditions i.e. small avalanches initiating from skis or machine starting to entrain snow. Plan your route to avoid travel on or under steep, solar slopes later in the day and recognize that the greenhouse effect could warm shaded aspects in the Alpine as well. Choose terrain carefully! 

 

Do you know what aspect you are on? What elevation are you traveling at? Do you need to travel on or under snow that is heating up? Looking towards Taylor Pass, 3-25-19

 

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

Yesterday we received a report of a large natural slab avalanche that was observed running later in the day in terrain north of Girdwood. The details are limited but this was on a southeast aspect around 4500′ and was classified as a D3, which is quite large and destructive. It was wide and the crown was deep. Although this is out of the Advisory Area, and may be somewhat of an outlier type of avalanche, it is important to remember that the colder snow in the Alpine is now getting warmed by direct sunshine and rising temperatures. Again, avoiding travel on or under steep, solar aspects later in the day is prudent at this time of year. The warming of the potential slab also adds to the lingering concern of triggering an avalanche that fails on an old persistent weak layer. Finding the trigger spot in a thin area of the snowpack could produce a very large avalanche. Signs of instability won’t necessarily be present with this type of avalanche problem. Use good travel protocol and think about consequences if a slope does slide. It could be the 1st or 10th skier or machine on the slope that triggers the avalanche. In addition, if traveling in the Alpine look for areas that are more wind-loaded, watch for cracking and listen/feel for hollow snow indicating wind slabs in upper elevation terrain. 

CORNICES:  Cornices are very large and warm air temperatures and direct sunshine could destabilize them today. They have the potential to trigger very large avalanche on the slopes below and break way farther back than expected. Give them a wide berth. 

Deep avalanche in 20-Mile that ran during the last storm, photo: 3-25-19. Deep persistent slab avalanches continue to be a concern. 

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

There were a few new glide avalanches observed in the Girdwood Valley yesterday and many glide cracks are opening around the advisory area. These are very unpredictable and not triggered by humans. Glide avalanches fail at the ground pulling out the entire season’s snowpack and could be very dangerous. The only way to avoid this hazard is by not spending time under terrain with glide cracks. 

Glide cracks on Seattle Ridge that could run into traveled terrain. 3-25-19. Avoid spending time underneath glide cracks! 

Mountain Weather

Yesterday: Mostly sunny skies with highs in the 40Fs at lower elevations and highs in the 30Fs at upper elevations. Overnight temperatures barely dipped below freezing on a few weather stations but generally temperatures were in the mid to high 30Fs. Skies were mostly clear initially but became partly cloudy and winds were easterly 5-10 mph with gusts into the teens.  

Today: Skies are forecast to be partly sunny with temperatures in the Alpine in the mid to high 30Fs and temperatures in the 40Fs at lower elevations. Winds will remain easterly 5-15 mph with gusts into the teens. Overnight will be partly cloudy becoming mostly clear. Temperatures will be in the high 20Fs to mid 30Fs.  

Tomorrow: More sunshine and warm temperatures with clouds building overnight. Cloudy skies will continue Friday but will clear for the weekend as the next ridge of high pressure sets up and dictates the weather into next week.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36   0   0   70  
Summit Lake (1400′)  34     0    0     23  
Alyeska Mid (1700′)  36     0   0   65  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  28  W 6   30  
Seattle Ridge (2400′)   34    variable 2   20