ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Tuesday January 29th, 2019
Posted by Wendy Wagner on 01/29/19 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 remains CONSIDERABLE  on slopes above 1,500′. Fresh wind slabs and cornice falls, due to strong wind and 6-12″ of new snow overnight, may release naturally along ridgelines and  human triggered avalanches will be likely. The new snow and wind loading  may also overload and trigger much larger avalanches  that break in a weak layer of buried surface hoar sitting 2-5′ below the surface. Continued cautious route finding and conservative decision-making will be essential for a safe day in the mountains.  

SUMMIT LAKE / JOHNSON PASS:    Natural avalanches are possible and human triggered avalanches are likely due to  strong wind, 4-6″ of new snow and a poor snowpack structure.  

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.
1. Low
Below Treeline
/ Below 1,000'
Avalanche risk
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Special Announcements

  • Remember 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 the CNFAIC. We rely heavily on your support, thank you to all of our donors, past, present and future!
  • *Early Bird Special* tickets are only $25 for the 5th annual SNOWBALL until midnight January 31!!  Get them now, this show sells out! Snowball is our fun way of saying thank you and celebrating another great season together. Click  HERE  for tickets!
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

New snow overnight with an additional 3-6″ expected today along with strong ridgetop winds are overloading the tenuous snowpack. If you’ve been following along, you’ll know that a weak layer of buried surface hoar sat 1-3′ below the surface before this new snow. The layer was highly reactive during last weekend’s clear skies and resulted in nine human triggered avalanches. Today, we will see how reactive it still is with another shot of stress by new snow and wind loading. 

Total snowfall as of 6am this morning for the past 24-hours:

  • Turnagain Pass – SNOTEL (1800’):  4″ at station, 6-8″ estimated above 2,500′
  • Girdwood – Alyeska Midway (1700’):  5″ at station, 10-12″ estimated above 2,500′
  • Portage – Bear Valley Tunnel (100’):  1.7″ of rain, 16″ – 2′ estimated above 2,500′
  • Summit Lake – SNOTEL (1400′):  4″ at station, 5-6″ estimated above 2,500′

Wind loaded slopes above 1,500′ are the most suspect for both naturally occurring avalanches and human triggered avalanches. Below 1,500′ the snowpack is composed of mostly crusts and avalanches are unlikely. Although fresh wind slabs and cornice falls may be the most common avalanche today, the more dangerous avalanche is the one that breaks deeper in the snowpack. If you are headed into the mountains and skies clear enough for travel above treeline keep in mind:

1-  Large avalanches have the potential to occur naturally and send debris to valley floors
2-  Fresh wind slabs and cornice falls may step-down and trigger a large avalanche
3-  Sticking to lower angel slopes, less than 30 degrees, with nothing steeper above you is a way to avoid these dangerous avalanche conditions. 

 

Storm snow avalanches from last week’s storm cycle in Lynx Creek Drainage (1/25). The debris in these slides covered the route into the upper portion of the valley. Additional slides like this are expected off steep ridgelines today. 

 

The thin gray line easily seen about a foot deep in the pit wall is the MLK buried surface hoar responsible for the rash of human triggered avalanches last Saturday and our worrisome weak layer being overloaded today. (Lynx Creek Drainage, 1/27/19, 2,800′ north aspect)

Avalanche Problem 2
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

Ridgetop winds have been blowing strong out of the east (20-35mph) for the past 24-hours. We can expect fresh wind slabs and cornices to be forming as winds transport not only the new snow but older soft snow. Wind slabs are likely to be in the 1-2′ foot deep range and easily triggered. This is also a prime condition for step-down avalanches. Meaning a fresh wind slab that triggers a deeper slab underneath. One that breaks 2-5′ deeper in the pack creating a much larger and dangerous avalanche. 

Mountain Weather

Yesterday:   Overcast skies with light rain below ~500′ and light snow flurries above dominated yesterday. Snowfall increased overnight with a total 24-hour accumulation of between 3-6″ at mid-elevations as of 6am this morning. Ridgetop winds have been strong, averaging 20-35mph from the east with gusts to the 60’s, for the past 24-hours. Temperatures have been in the upper 30’s to 40F at sea level, 32F near 1,000′ and in the mid 20’sF along ridgelines.  

Today:   Cloudy skies with snow falling above ~500′, rain below, is expected to continue through today. The mountains should see between 3 and 6″ of snow (.3 and .5″ of water equivalent) today with an additional 2-3″ tonight (~.25 water). Ridgetop winds are expected to remain in the 20-35mph range from the east. Temperatures look to sit in the upper 30’sF at sea level, in the low-30’sF at 1,000′ and mid-20’sF along ridgetops.

Tomorrow:    The low pressure systems and associated fronts look to move north tomorrow decreasing ridgetop winds and snowfall. We could see some flurries tomorrow before skies begin to break. A return to clearer skies and cooler temperatures heads into the region for Thursday/Friday.    

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.   We are currently working to replace it.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   3    0.4 60  
Summit Lake (1400′) 32   4     0.3   24  
Alyeska Mid (1700′) 32   5   0.8   48  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   NE   24   62  
Seattle Ridge (2400′) 28   *N/A   *N/A     *N/A