Mon, December 28, 2015 Turnagain Pass Avalanche Forecast

Mon, December 28th, 2015

Alpine
Above 2,500'

High (4)

Treeline
1,000'-2,500'

High (4)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		High (4)
Treeline 1,000'-2,500'		High (4)
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

After a break in storm systems yesterday, we have another strong Pacific storm over us currently. This system is a bit warmer and bringing varying snowfall amounts around the region. The rain/snow line is hovering around 800′ (good news for keeping the snow at Turnagain Pass, which is at 1,000′). It is also a “Girdwood Special” as far as snowfall totals go: Girdwood Valley has picked up 16″ so far, Turnagain Pass 8″ with Summit Lake only seeing 2-3″. Snowfall will continue through the day with an additional 8-14″ expected.

What this all means for avalanche conditions is another HIGH hazard day in the backcountry. If you are considering heading out keep in mind:

1) Natural wind slab avalanches are likely on slopes being loaded by the winds. These will be 1-3′ thick and have the potential to break into older snow.

2) If slides break into older weak layers, we could see very large avalanches, up to 6′ thick (more on this below).

3) In sheltered areas, out of the wind, slabs up to 2′ thick are still possible due to a layer of surface hoar and near surface facets that sat 10-15″ below the surface yesterday. Very careful snowpack assessment is needed if you are in a sheltered zone – in the Tincan Trees for example.

4) Cornices: With such strong winds and warm snow at the high elevations, we can expect cornices to be forming and breaking off. These ‘backcountry bombs’ are likely triggering avalanches below. Even if the winds subside today, these can still break naturally

Avalanche Problem 2

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

There are two older weak layers in the pack we are watching. These can be seen in the photo below. Both layers are composed of a mix of surface hoar and near surface facets. These are persistent grains types that can produce large avalanches during, and after, a ‘rapid loading’ event such as today. If today isn’t enough load, then possibly the next storm cycle coming tomorrow through Wednesday. An avalanche breaking this deep in the pack can be very large, connect across terrain features and run to valley bottoms. We are unsure if this could happen today, but it is definitely on our minds.

Weather

Mon, December 28th, 2015

Overcast skies, light snowfall and moderate to strong winds covered the region yesterday. Only around 1-2″ of snow accumulated with rain falling below ~600′. Ridgetop winds averaged in the 20’s mph from the East with gusts in the 40’s mph.

Overnight, a strong low pressure system moved into the Gulf and is bringing warm air and moisture with it. See the Satellite image below. Sunburst is averaging Northeast winds in the 60’s this morning with a peak gust of 110mph! The rain snow line has crept up to ~800 feet and models are showing it rising to 1200 feet today. Precipitation amounts vary significantly across the region, see the 24-hour charts below. The storm will begin to move out today but strong Easterly ridgetop winds and lingering snowfall (rain below 1200′) will remain. Ridgetop winds are slated to average in the 30-40’s mph with another 8-14″ of snow above treeline and around 1″ of rain at sea level.

Another warm, wet and windy storm is on tap for Tuesday and Wednesday. We are watching the rain/snow line closely and so far it looks to fluctuate between 500 and 1200′ for this one.

Image below is from the NWS: 5am infrared satellite picture of the strong Pacific storm over us today.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	8	0.7	68
Summit Lake (1400′)	32	2	0.3	19
Alyeska Mid (1700′)	31	16	1.35	57

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	23	NE	38	110
Seattle Ridge (2400′)	25	N/A	N/A	N/A

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.