ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday February 16th, 2019
Posted by Wendy Wagner on 02/16/19 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  at all elevations and expected to rise to CONSIDERABLE tomorrow. New snow and wind is on the way and may create fresh wind slabs, up to 6-10″ thick, by sunset in areas seeing 4-6″ of new snow. New snow sluffing off steep slopes should also be expected. Additionally, triggering a larger slab avalanche 1-3′ thick that breaks in weak snow deeper in the snowpack remains unlikely, but is not out of the question. Give cornices a wide berth, and avoid travel under glide cracks.

SUMMIT LAKE / COOPER LANDING:   Central and Western Kenai mountains may see snow amounts from 4-8″ today. This area has a very poor snowpack with multiple weak layers. New snow avalanches are a concern, but triggering a slab 1-3′ thick, breaking deeper in the snowpack is a much more dangerous problem. Watch for whumpfing, shooting cracks and recent avalanches.

SEWARD/ LOST LAKE:   Higher snowfall amounts are expected in the Seward zone, possibly over a foot today. Heads up that storm snow avalanches will be likely once snow accumulates to over 6″.

BYRON GLACIER TRAIL Hikers:    Natural avalanches may send debris to valley floors by Sunday. Avoid being in the runout paths. Also, the popular snow cave is very dangerous and unstable. See this video from Valentines Day!

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.
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

  • New snow and wind will increase the avalanche danger region-wide.  Heading to Hatcher Pass? GET the forecast! Check out  the Hatcher Pass Avalanche Center Saturday Advisory click  HERE.
Avalanche Problem 1
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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
    Storm Slabs
  • Chance
    Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size
    Historic
    Very Large
    Large
    Small

The National Weather Service has issued a Winter Weather Advisory from Girdwood to Seward beginning at 0800 this morning. After 11 days with nearly no new snow and strong northwest outflow winds wreaking havoc on Wednesday, snowfall this weekend is a welcomed relief. The current snow surface is less than ideal, described in yesterday’s reports as “scoured, boney, pretty terrible, difficult to find any soft snow”, I’ll stop there. Snowfall should begin midday with 1-4″ falling by sunset, with more possible in favored areas such as Portage Valley. An additional 4-8″ is expected overnight. Snow should make it to sea level with the cool temperatures in place. 

Today is a ‘watch for changing weather’ day. Avalanche danger will increase in sync with new snowfall and wind. The hard existing snow surface will make inital bonding with the new snow poor. Once snow piles up to a good 4-6″ we can expect easily triggered sluffs on steep slopes and shallow wind slabs along ridgelines. With lower snow amounts today, fresh wind slabs should be in the 6-10″ range, relatively small. As temperatures climb and when new snow accumulates to over 6″, we could start seeing storm slabs in areas out of the wind. This issue is more likely to be seen overnight and into Sunday. 

 

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

Roughly 1-3′ below the old hard wind affected surface sits a layer of buried surface hoar and in some areas facets. The layer of buried surface hoar was responsible for several large avalanches triggered a couple weeks ago and has slowly become unreactive. New snow this weekend and more through the week will be adding a load, and hence additional stress, onto these buried weak layers. Our concern is, will these layers become reactive again? In areas near Summit Lake the potential is higher for triggering a large slab breaking in old snow due to a weaker snowpack. As we move forward with new snow and stoke, we can’t forget there are some hidden dragons, especially in thin snowpack zones. 

If you’re headed into the mountains and visibility is good enough for travel above treeline, keep in mind:

  1. Wind loaded steep features, large connected and unsupported slopes are the most suspect.
  2. There is more potential for triggering a large slab in Summit Lake, Johnson Pass and Lynx Creek due to a generally thinner and weaker snowpack.
  3. Use safe travel protocol. Expose 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.

  

Alaska Avalanche School’s Level 2 snowmachine course investigates the currently unreactive layer of buried surface hoar in God’s Country of Seattle Ridge. The photo on the right is also from the course and illustrates the hard wind affected surface that this weekend’s new snow will be falling on (don’t be fooled, those tracks are raised anit-tracks!).

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 still on the move. Two glide cracks released into avalanches this week, one near the Hope Wye and another in Girdwood Valley. Several cracks threaten popular routes on the South facing slopes of Lipps and Magnum. There is also a new glide crack opening on Seattle Ridge on Repeat Offender. Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.

Big thanks to Tom Enzi for capturing this photo of a large glide crack on SW facing Magnum ridge yesterday (2/15). This crack has been slowly opening for several weeks. 

Mountain Weather

Yesterday:   Mostly clear skies with light and variable ridgetop winds. Temperatures remained generally in the 5-15F range at all elevations for the day. While cold air has remained at the lower elevations, temperatures have climbed overnight above treeline from the single digits to 20F.  

Today:   Clouds have moved in, temperatures continue to rise and snowfall – to sea level – is expected to begin mid-day. Between 1 to 4” of snow is expected today with an additional 4 to 8″ tonight.  Ridgetop winds have turned easterly this morning and expected to pick up to the 30-40’s mph from the east with stronger gusts through today and into tomorrow. Temperatures look to hover in the 20’sF at all elevations.

Tomorrow:   Snowfall and wind will continue through tomorrow. Another 2-4″ is expected through the day before tapering off Sunday night. Temperatures will continue a slow rise and we could see a rain/snow mix at sea level.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15   0   0 56  
Summit Lake (1400′) 6   0   0   24  
Alyeska Mid (1700′) 14   0   0   50  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13   variable   6   23 (east)
Seattle Ridge (2400′) 12   variable   5   17 (east)