Mon, December 31, 2018 Turnagain Pass Avalanche Forecast

Mon, December 31st, 2018

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

Storm Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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

Human triggered (skier or snowmachiner) storm slabs are likely today on slopes steeper than 30 degrees. The first in the series of storms forecast to impact the area is moving out this morning. The storm brought sustained strong winds yesterday and last night and heavy snow overnight. Do not let the potential for decent visibility today lure you into avalanche terrain. Look for signs of instability. Recent avalanches are the best clue that the snowpack is unstable.

24-hour precipitation and wind:

Turnagain Pass SNOTEL: 15″ (1.3″ SWE), Sunburst wx station winds: NE, 25-40 mph, gusting to 102
Girdwood – Alyeska Midway: 20” (1.5” SWE), Max’s wx station winds: E-NE 25-40 mph, gusting to 92
Summit Lake: 3-6″ (0.3” SWE)

With the strong winds and new snow we expect a buffet of storm related avalanche issues today. New snow was landing on a layer of surface hoar and may not bond well to the old snow. The temperatures increased during the storm putting heavier snow over lighter snow. Storm slabs may be very sensitive. Look for cracking and collapsing. With the buried surface hoar potential these slabs may be very reactive even on slopes in the Tincan Trees. Remote triggering may be possible. Avoid travel in runout zones.

Wind slabs: Strong winds will have the blown snow into the leeward start zones. Due to the high wind speeds slabs may have formed further down the slope than expected. Look for pillowing, drifting and cracking. Be suspect of hollow sounding snow or hard snow over soft snow.

Cornices: High winds and blowing snow will have added to already large cornices. These may be very sensitive and a cornice fall could trigger a large avalanche on the slope below. Remember these can break further back than expected.

Heavy snow overnight on Turnagain Pass.

Surface hoar observed 12-28-18, Photo: Trip Kinney

Avalanche Problem 2

Glide Avalanches
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

Likelihood of Avalanches

Size of Avalanches

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

Glide avalanches have been releasing over the past week. Remember these avalanches are not triggered by people and are unpredictable. The most recent release of a glide crack (glide avalanche) was noted Saturday on Lipps. The new snow may have covered some of the glide cracks up. Don’t forget they are looming over popular ski and snowmachine terrain and limit as much time under them as possible! The glide cracks are on the move… Don’t mess with the brown frown!

Lipps glide avalanche, 12-29-18. Photo: Andy Moderow

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

South of Turnagain: As we have been mentioning for some time, a shallow and poor snowpack structure exists in the Summit Lake zone. Buried weak layers of facets associated with crusts sit 1-3′ below the surface near the base of the snowpack. Although Summit did not get much precipitation in this first storm it will be important not to forget the possibility of triggering a larger avalanche that could release near the ground if recreating in that zone. Check out the Summit observations HERE for the most current information.

Weather

Mon, December 31st, 2018

Yesterday: Skies were overcast to obscured with snow and rain showers throughout the day intensifying overnight. Rain/snow line was around 500′. Winds were easterly 25-40 mph gusting as high as 102 on Sunburst. Temperatures were in the 20Fs to mid 30Fs.

Today: Skies will be mostly to partly cloudy. There is a chance of snow showers during the day. Winds will be easterly10-20 mph with gusts into the 30s. They shift to the north this afternoon and ease up briefly. Temperatures will be in the high 20Fs to mid 30Fs. This evening the next storm moves into the area with easterly winds increasing 20-40 mph gusting into the 50s. Precipitation may be heavy again with rain/snow line around 800′-1000′.

Tomorrow: Rain and snow in the morning decreasing in the afternoon. Winds will decrease as well. Temperatures will be in the high 20Fs to high 30Fs. The pattern remains active for the week but the model confidence remains low. Stay tuned for storm details.

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	15	1.3	67
Summit Lake (1400′)	30	3	0.3	15
Alyeska Mid (1700′)	30	20	1.5	55

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	NE	38	102
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.