Mon, December 10, 2018 Turnagain Pass Avalanche Forecast

Mon, December 10th, 2018

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Low (1)

Below Treeline
Below 1,000'

Low (1)

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

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Avalanche Problem 1

Wind Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Easterly winds blowing 15-30 mph with gusts into the 50s overnight will have moved any soft storm snow left available to transport into leeward areas. Additional snow falling today may also get blown around with 1-4″ in the forecast. Wind effect from the very strong winds during the wet storm on Friday and Saturday was evident in the Alpine yesterday. However, there was minimal signs of wind slab. Today that may have changed, wind-loaded, steep unsupported slopes above 2500′ may be tender. Look for stiff, pillowed snow and cracking and listen for hollow, drum-like sounds. Loading patterns can be very localized and it is crucial to look for clues indicating where the snow is being distributed.

Wind effect on the Tincan uptrack, 12-9-18

Additional Concern

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

Observations yesterday in Turnagain Pass found signs that the storm snow is bonding well to the old snow surfaces. We do not have evidence that there currently is a persistent weak layer issue in the this core area of the advisory zone. Above 2,500′ there is a thin layer of buried surface hoar anywhere from 2-5′ deep in the snowpack but it is not showing signs of reactivity and at this point is being regarded as a dormant layer to track. As we move south and the snowpack is shallower, the potential to trigger a persistent slab avalanche on weak snow near the ground increases. Observations prior to the storm showed weak facets in Summit Lake. If traveling in this area the likelihood of triggering a dangerous avalanche remains. Choose terrain carefully.

Red flags to watch for:
– Recent avalanches
– Whumpfing (collapsing) of the snowpack, a sign to avoid avalanche terrain.
– Shooting cracks, likely to be seen near ridgelines where the wind has formed wind slabs.

Summit snowpack observation: Tenderfoot, 12-3-18

Weather

Mon, December 10th, 2018

Yesterday: Skies were mostly clear and sunny. Temperatures were in the 20Fs to mid teens. Winds during the day were light and variable. Overnight easterly winds picked up blowing 15-30 mph with gusts into the 50s. Temperatures initially cooled into the evening and then rose again in the early morning into the 20Fs and low 30Fs.

Today: Cloudy skies and snow showers throughout the day. 1-4″ of snow above 300′. Easterly winds 10-20 mph with gusts into the 30s. Temperatures in the low 30Fs to mid 20Fs. Continued snow showers overnight with snow to sea level, 2-5″.

Tomorrow: Continued snow showers with more cold air moving into the region Tuesday night. From the National Weather Service: The colder air which moved across the Gulf and Southcentral yesterday was the beginning of what appears to be a prolonged shift to a more “typical” Alaska weather regime for this time of year. There are a number of features in the forecast that we will keep tabs on for the week! Stay tuned. Timing and precipitation amounts are still uncertain.

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	24	1	0.1	26
Summit Lake (1400′)	19	0	0	4
Alyeska Mid (1700′)	24	0	0	8

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	14	NE	12	53
Seattle Ridge (2400′)	20	*no data	*no data	*no data

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 Sat, September 23rd, 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	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Placer River	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Skookum Drainage	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Turnagain Pass	Closed	Scheduled opening on the Wednesday before Thanksgiving per Chugach National Forest plan. Subject to adequate snow cover.
Twentymile	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Seward District
Carter Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Lost Lake Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Primrose Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Resurrection Pass Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Snug Harbor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
South Fork Snow River Corridor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Summit Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.