Sat, February 23, 2013 Turnagain Pass Avalanche Forecast

Sat, February 23rd, 2013

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		Considerable (3)
Treeline 1,000'-2,500'		Moderate (2)
Below Treeline Below 1,000'		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 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 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

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/22/23	Turnagain	Avalanche: Tincan	Nick D'Alessio
05/12/23	Turnagain	Avalanche: Tincan, Sunburst, Magnum, Cornbiscuit	Heather Thamm
05/07/23	Turnagain	Observation: Tincan – Bear Tracks	CNFAIC Staff
05/05/23	Turnagain	Observation: Seattle Ridge	AS/ WW Forecaster
05/02/23	Turnagain	Observation: Cornbiscuit	Schauer/ Sturgess Forecaster
05/02/23	Turnagain	Observation: Seward Hwy Turnagain Pass	Joel Curtis
04/30/23	Turnagain	Observation: Magnum	Ayla, Kit Crosby, Barton
04/29/23	Turnagain	Observation: Tincan	John Sykes
04/28/23	Turnagain	Avalanche: Taylor Pass/Pastoral	Schauer/ Creighton Forecaster
04/28/23	Turnagain	Avalanche: Tincan	Andy Moderow

Riding Areas

Updated Thu, June 01st, 2023

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	Closed May 15.
Placer River	Closed	Closed May 15.
Skookum Drainage	Closed	Will close to motorized use on April 1, 2023 per the National Forest Plan.
Turnagain Pass	Closed	Will close on June 1.
Twentymile	Closed	Scheduled closure May 1.
Seward District
Carter Lake	Closed	Scheduled closure May 1.
Lost Lake Trail	Closed	Scheduled closure May 1.
Primrose Trail	Closed	Scheduled closure May 1.
Resurrection Pass Trail	Closed	Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor	Closed	Extended opening until May 15.
South Fork Snow River Corridor	Closed	Scheduled closure May 1.
Summit Lake	Closed	Scheduled closure May 1.