ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Saturday March 9th, 2019
Posted by Wendy Wagner on 03/09/19 at 7:00 am.
The Bottom Line
High Avalanche Danger
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

The avalanche danger is CONSIDERABLE  this morning due to 1-2 feet of new snow in the past 24-hours. The danger is expected to rise to HIGH this evening as another round of snow and wind moves in. Human triggered slab avalanches, up to 2+ feet thick, will be likely. Natural avalanches will be possible. The new snow is falling on a very weak base and expected to slide easily on steep slopes.  We are entering spring break with a dangerous avalanche situation and restraint will be required as travel in avalanche terrain is not recommended.  

PORTAGE VALLEY:  Natural avalanches are possible today that could send debris to valley floors. Areas with steep slopes and avalanche terrain above you, such as the Byron Glacier Trail, should be avoided.

SUMMIT LAKE:   Despite little new snow, this area has a very shallow snowpack with multiple weak layers. Strong winds and the potential for a few inches of new snow today could overload buried weak layers, producing an unexpected slab avalanche. Caution is advised if heading to this area.

LOST LAKE:    Dangerous avalanche conditions are expected in the Lost Lake and Seward regions as well due to 1-2 feet of new snow and strong winds.  

4. High
Alpine
/ Above 2,500'
Avalanche risk
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4. High
Treeline
/ 1,000'-2,500'
Avalanche risk
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3. Considerable
Below Treeline
/ Below 1,000'
Avalanche risk
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Special Announcements

  • If you’re headed to Alyeska today, bring your avalanche beacon. Backcountry Access (BCA) and Alyeska Ski Resort will have a beacon training park set up all day on March 9, March 23, and April 6. Check in at any Ski Patrol station or visit the  Snow Report  for the location of the search park.
  • Heading to Hatcher Pass? Be sure to check out the Hatcher Pass Avalanche Center Saturday avalanche forecast  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

It’s a simple equation:  new snow falling on a slippery surface + wind loading = easily triggered avalanches.

Heads up for anyone headed out today. Storm snow avalanches are expected to be easily triggered. These will be in the form of wind slabs on wind loaded slopes, storm slabs in areas out of the wind, cornice falls and new snow sluffs. The size of the avalanche will depend on the amount of new snow and wind loading. In the Girdwood Valley slabs could be up to 3′ thick on wind loaded slopes. In the Turnagain Pass area, slabs could be up to 2′ thick. Come tomorrow, add another 10-20″ to the thickness of these slabs. 

Although hidden from view, under the storm snow is the old surface, which is a combination of sun and wind crusts, facets and surface hoar. Not only will this old surface inhibit bonding with the new snow, it may also allow slabs to propagate wider than expected. Remotely triggered avalanches are also possible, meaning triggering a slide from the ridge or the bottom of a slope. With another round of snow and wind slated to hit later today, pushing the danger to HIGH, now is the time for us to keep out of avalanche terrain and let the mountains do their thing. 

Estimated storm totals (mid-upper elevations) beginning Thursday ending Saturday 6am:

  • Turnagain Pass:  10″ – 16″ snow (1″ water)
  • Girdwood Valley:  16 – 24″ snow (1.5 – 2.3″ water)
  • Summit Lake:  1-2″ snow (0 – 0.1 water)
  • Bear Valley (Portage):  20 – 30″ snow (2 – 2.5″ water)
  • Seward area:  12″ – 20″ snow (1-1.5″ water)

 Rain has been falling below 1,000′ and expected to continue today. This whas saturated the low elevations and wet sluffs will be possible. 

Storm slab avalanche in the Tincan Trees from yesterday. Roughly 6 more inches of snow has fallen with more on the way, which will create much larger slabs for today. Photo: Allen Dahl.

 

The photo above shows the 6-8″ of new snow from yesterday sliding easily on the old sun crust that was the surface a few days ago. (Photo: Allen Dahl)

Mountain Weather

Yesterday:   Light to heavy snowfall was over the region as the second storm front passed through. Rain fell up to 500′ and in some areas up to 1,000′. Snowfall amounts across the region varied greatly from only a trace in the Summit Lake area to over 2 feet in the upper Girdwood and Portage Valleys. Turnagain Pass has seen around a foot of new snow. Ridgetop winds over the past 24-hours have been blowing 20-30mph from the east with stronger gusts. Temperatures have been steady in the low to mid 20’sF along ridgelines and in the mid 30’sF near sea level.

Today:   A brief break between storms is expected this morning with the third wave of precipitation moving in midday and peaking late tonight. An additional 3-6″ of snow is expected to fall today with 10-14″ tonight. The snow/rain line should creep up to 1,500′ in areas and therefore, rain will be falling at the low elevations. Ridgetop winds are forecast to remain easterly in the 20-30mph range with gusts up to 50mph. Temperatures may reach the upper 40F at sea level, 32 at the mid elevations and the mid 20’sF along ridgelines.

Tomorrow:    Stormy weather will continue Sunday and into Monday with an additional 6-12″ of snow at the mid and upper elevations. Cooler air looks to be entrained on Monday, which will lower the rain line and snow could fall near sea level. Another small break in storms may occur Tuesday before another round of precipitation hits. Stay tuned!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   10   0.8 63  
Summit Lake (1400′) 33   trace    0 26  
Alyeska Mid (1700′) 30   14   1.05   67  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   NE   29   57  
Seattle Ridge (2400′) 27   SE   14   27