Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 15th, 2014 - 7:00AM
Expires
Sun, March 16th, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Since Monday Turnagain Pass has another ~50 inches of snow on the ground.   This has come through 2 storms €“ one that started Monday, the other that just tapered off late last night.    

This is a huge additional burden for the snowpack to hold.  The kicker is that this new snow is sitting on a persistent weak layer above the February melt/freeze crust.  Avalanche danger will be  CONSIDERABLE  at all elevations.

 Partly cloudy skies and a fresh blanket of snow will make for an enticing combination today.   This is not an “anything goes” kind of day.  Conservative terrain choices will be essential today.

 Avalanches may be difficult to trigger, but if you get something to move it’s going to be big and dangerous.

Special Announcements

Placer river and Skookum are  CLOSED  to motorized use from the rain this week.  Seward district riding areas are  OPEN.  Check the bottom of this page for the latest information on riding areas.

Sat, March 15th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
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.
More info at Avalanche.org

It’s been snowing – a lot!  Anchorage got a significant dump last night.  That snow extended to Girdwood and beyond.  This is the kind of maritime storm pattern that we are famous for, and we’ve been missing during this drought winter.  

The storm snow problem is least stable during the active part of the storm, and tends to stabilize quickly over time.  The big message today is that we got a LOT of snow and it will need time to settle out, bond, and stabilize.  We are still within the 24 hour window since active storming, and still within the window of high probability to trigger avalanches in the new storm layers.  

Storms also create wind slabs and build cornices.  Cornices are likely to be bigger and less stable than they were last weeekend.

Time will make these storm layers stable, but today is not the day to test them in big and dangerous terrain.  

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

Underneath all the fresh snow from the last 5 days is the prominent crust layer that formed in February.  Just above this crust is a weak layer of faceted snow mixed with buried surface hoar.  

We did some snow pit testing yesterday.  Results indicated the most concerning weak layer (above the Feb. crust) is difficult to initiate, but propagation potential is high.  The triggering is difficult because our slab layer (40-50 inches of new snow) is thick and strong.  This information tells us that avalanches may be difficult to trigger, but when they do the resulting avalanche can be large and deep.  

This kind of deep slab problem is most likely to be triggered from an area of shallower snow.  Wind loading patterns during the storm caused scoured ridges which quickly transition to deeply loaded slopes on the downwind side.  A skier or snowmachiner is more likely to trigger this problem near the scoured ridge than far into the deep pocket.  Once initiated, it could propagate across into the deeper snow.

Larger triggers are also more likely to initiate the deep slab.  Snowmachines have the disadvantage here with 600+ pounds of sled and rider weight impacting the slope.  

Weather
Sat, March 15th, 2014

This has been a great week for snowfall.  Turnagain Pass more than doubled the total snow on the ground from 42 inches on Sunday to 88 inches last night.  Total new snow water equivalent is 5.9 inches.  Wind during the storm was predominately from the east on Sunburst.  Rain did reach up above 1000 feet at times during the storms, but the snow dried out at the tail end of the storm all the way to sea level.  

Last night we got a final shot of snow during a cooling temperature trend.  This last bit of the storm was widespread from Anchorage to eastern Turnagain Arm.  

A chance of snow continues today, with a couple more inches possible.  Decreasing clouds through the day may allow the sun to poke through at times.  Temperatures should be cooler, in the low 20s.  Wind will be light from the south.  

Observations
Recent Observations for Turnagain Pass
Date Region Location
05/13/24 Turnagain Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South
05/13/24 Turnagain Observation: Turnagain Pass non-motorized side
05/12/24 Turnagain Observation: Warm up Bowl
05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs
04/29/24 Turnagain Avalanche: Turnagain aerial obs
04/27/24 Turnagain Observation: Johnson Pass
04/23/24 Turnagain Observation: Turnagain Sunny Side
04/21/24 Turnagain Observation: Bertha Creek
04/20/24 Turnagain Avalanche: Spokane Creek
04/16/24 Turnagain Observation: Cornbiscuit
Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.


Subscribe to Turnagain Pass
Avalanche Forecast by Email

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.