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Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 23rd, 2013 - 7:00AM
Expires
Sun, February 24th, 2013 - 7:00AM
Forecaster
Kevin Wright
The Bottom Line

Today’s avalanche forecast is largely based on the weather forecast.   A blizzard warning is in effect, meaning severe winter weather is expected or occuring.   The danger rating will start out as MODERATE above treeline this morning, and transition to CONSIDERABLE if storm snow builds to the 10 inches that may accumulate by this afternoon.  

Avalanches today will be low volume and shallow in depth, but will be found in many areas.   The main concern to backcountry travelers won’t develop until later today.

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Sat, February 23rd, 2013
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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

Building storm snow, combined with wind today will add a new slab on top of an already loose and weak surface.  We can expect tender soft slabs from wind buildup today to travel far and fast, but initially low volume.  We have a couple questions to answer while in the backcountry today.

1.  How much snow is building from today’s storm?

2.  How is the new snow bonding to the old snow?

If the answer is “lots of new snow” and “poor bonding”, then the danger rating will be bumping into CONSIDERABLE by the afternoon today. 

Yesterday we saw medium size natural and skier triggered sluffs, with a few small slabs from wind (see picture below from Pete’s South).  With new snow expected today, we can expect a similar avalanche character but on a larger scale.  Loose snow sluffs are likely, and soft wind slabs 1-2 feet deep are possible by this afternoon.

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

I was almost ready to drop the discussion about persistent weak layers, then Wendy and Sean found a great example of this problem lingering in Turnagain Pass yesterday.  We still consider this problem to be isolated, but the red flags and pit results indicate that those isolated areas may still be triggerable by a person.  This problem is from the late January crust that produced a weak layer between 1900 and 3000 feet and has been responsible for a handful of human triggered avalanches.   Be aware of this problem at mid-elevations and especially in areas with a thinner snowpack where the weight of a person could collapse the problem weak layer.

Weather
Sat, February 23rd, 2013

Yesterday was sunny, with a little wind up high.   The sun from the last 2 days has just barely added a crust to direct south facing aspects, thin enough that it’s not a big issue for skiing quality.   Wind had enough force to build and trigger some very shallow slabs in steep terrain.  

Today, a blizzard warning is in effect until 4pm.   5-10 inches of snow are predicted for the mountains of Turnagain Arm, with east wind 35-45mph.   Temperatures should remain cold enough for snow to sea level.   The front responsible for today’s blizzard will pass by this evening, but snow showers remain in the forecast for tonight and the next several days.


Wendy will issue the next advisory tomorrow morning, February 24th.

Observations
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Date Region Location
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Riding Areas
Updated Mon, October 26th, 2020

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.