Wed, February 19, 2014 Turnagain Pass Avalanche Forecast

Wed, February 19th, 2014

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Considerable (3)

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

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Avalanche Problem 1

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

We have received a plethora of snowpack and avalanche observations from the skier side of Turnagain pass over the last several days thanks in part to the Alaska Avalanche School hosting a couple different courses in the Turnagain region over the weekend. A common theme since Saturday has been parties remotely triggering avalanches that are failing on a thin layer of facets above the January rain crust. This persistent weak layer seems to be most evident at elevations greater than about 2500’.

With a moderate load of new snow overnight and forecasted through today, this known weak layer will move closer to its tipping point. Terrain (such as the backside of Seattle ridge, snowmachiner side) that has not seen much traffic this season warrants extra caution today as the weak snow in these areas has not been tested by skiers or snowmachiners like it has in areas such as Tin Can and Sunburst. Slopes greater than 35 degrees deserve a wide berth when travelling on or underneath, specifically for the possibility of remotely triggering an avalanche.

For sledders, there is a lot of fun to be had in the flats without exposing your party to avalanche terrain today.

Avalanche Problem 2

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

Snowfall amounts varied significantly during the last 24 hours across our zone with Girdwood picking up 12-16 inches, Turnagain pass picking up 1-2 inches and for comparison Anchorage accumulated about 6 inches. The lion’s share of this snow fell during a short but intense period yesterday evening and through the early morning hours though totals fell well short of the forecasted storm.

Storm slab avalanches will be of increased concern in areas that have seen favorable accumulation, spanning all elevations today. Included in this will be the possibility to trigger a wind slab on leeward slopes or cross-loaded gullies, as there is ample snow available for transport to build tender wind slabs. Though Turnagain saw less snow than other zones overnight, that area has been favored over the last several days of storms (since Friday).

Furthermore, loose snow avalanches are likely today in steep terrain above 35 degrees. Though usually a manageable problem, loose snow avalanches prove most hazardous when initiated above a terrain trap.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Cornices are growing quite large as of late. These “backcountry bombs” not only have a tendency to break much further back on a ridge than one expects but also have a great potential to initiate an avalanche on the slope below. Do not test your luck with cornices today (or ever for that matter!), as a fortunate outcome is highly unlikely.

*Note: The AKDOT webcam is working again on Turnagain Pass! Keep tabs on snowfall as well as the road conditions with this link.

Weather

Wed, February 19th, 2014

Though yesterday’s winter storm warning was canceled mid-day and we didn’t quite see forecasted snowfall amounts, there was a brief and intense burst of snowfall from about 5PM last night to 2AM this morning. Areas north of Turnagain pass including Whittier, Portage, Girdwood and Anchorage all woke up to measurable snowfall.

Yesterday in the core advisory area (Turnagain Pass), temperatures reached the mid to high 20’s with winds peaking around noon in the mid-20mph range. Skies were broken all day during the daylight hours with no snow accumulating during the day.

Today we can expect slightly cooler temperatures in the low to mid-20’s with light winds out of the south east. 2-4 inches of snow is expected throughout the day before tapering off into the overnight hours. Tomorrow looks to be the best chance for some sunny skies before we return to what appears to be an active weather pattern for the weekend.

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.