Sun, April 14, 2019 Turnagain Pass Avalanche Forecast

Sun, April 14th, 2019

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Low (1)

Below Treeline
Below 1,000'

No Rating (0)

Alpine Above 2,500'		Moderate (2)
Treeline 1,000'-2,500'		Low (1)
Below Treeline Below 1,000'		No Rating (0)

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Avalanche Problem 1

Wet Loose
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic

Very Large

Large

Small

Size

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

A couple sunny days are in the forecast and we are generally back into a springtime avalanche regime. Meaning, low hazard in the morning (frozen snow surface) transitioning to a moderate hazard in the afternoon on solar aspects (melting snow surface). Wet loose sluffs should be easy to trigger once sunny slopes warm enough to melt the top 2-3″ of frozen snow. If the surface becomes even more sloppy (6″ or more of wet/mushy snow) then sluffs could become larger and more dangerous, especially in larger terrain. Paying attention to surface warming/melting will be key for the next several days.

Other springtime concerns are cornice falls. Cornices heat up and can destabilize rapidly during daytime warming; making them easier to trigger.

Cornice along the Sunburst ridge yesterday.

Avalanche Problem 2

Persistent Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic

Very Large

Large

Small

Size

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.

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

In the dry snow that sits on shaded aspects generally above 3,000′, even over 3,500′ in places, a questionable weak layer exists 1-2′ below the surface. The layer is composed of facets and buried surface hoar and was found at 3,300′ on Tincan. It is suspect to be lurking on other high elevation northerly slopes. We had a good look around yesterday and did not see signs of natural avalanches breaking in the layer during last Thursday’s storm, which is good news, but we still need to tread cautiously. Listening for whumpfing and digging a test pit to look for and test the layer are good ways to gather information. Sticking to safe travel protocol is also wise; exposing one person a time, watching our partners and having escape routes planned.

Taylor Pass and Basketball Chute on the right. Many higher elevation northerly aspects remain intact. The only evidence of avalanche activity from Thursday’s storm were old wind slabs; no signs of avalanches breaking in deeper weak layers.

Additional Concern

Glide Avalanches

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.

More info at Avalanche.org

A few glide cracks that were filled with new snow on Thursday are slowly opening up again. This tells us some movement is still taking place. A chance remains that a crack could release into an avalanche. It has been a week since the last known glide released (Hope Wye area south of Turnagain). Being suspect of cracks and limiting/avoiding time spend under them is always a good idea as they can avalanche at any time.

Seattle Ridge with the up-track on the looker’s right of photo. After many glide avalanches turned this ridge brown, new snow has brightened it up a bit. It has been over a week now since any glide avalanches have occurred on this slope – that doesn’t mean one can’t occur today however.

Weather

Sun, April 14th, 2019

Yesterday: Partly cloudy skies were over the region as high pressure slowly built in. Ridgetop winds have been light over the past 24-hours, blowing 5-10mph from the east. Temperatures climbed to 30F at 4,000′ and to 40F at 2,000′. Clear skies have allowed overnight temperatures to cool to the upper 20’sF below 2,500′.

Today: Mostly sunny skies with light and variable winds are expected. Temperatures should climb to 32F, or higher, at 4,000′ and to the mid 40’sF at 2,000′.

Tomorrow: Monday we can expect another sunny day that could be slightly warmer than Sunday. Winds should remain light with an easterly push (~5mph). One more clear sky day for Tuesday before clouds and a chance for precipitation heads our way Wed/Thurs.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	34	0	0	64
Summit Lake (1400′)	32	0	0	18
Alyeska Mid (1700′)	34	0	0	58

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	26	NE	6	21
Seattle Ridge (2400′)	31	SE	4	10

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/28/22	Turnagain	Avalanche: Turnagain Pass – late May wet slab cycle	CNFAIC Staff
05/21/22	Turnagain	Avalanche: Magnum, Lipps and Tincan	CNFAIC Staff
05/17/22	Turnagain	Avalanche: Sunburst	CNFAIC Staff
05/17/22	Turnagain	Observation: Tincan Ridge	Joe Kurtak
05/11/22	Turnagain	Avalanche: Cornbiscuit and Magnum west faces	CNFAIC Staff Forecaster
05/07/22	Turnagain	Observation: Granddaddy	Kit Barton
04/29/22	Turnagain	Observation: Sunburst wx station	AS/ MM/ AM/ NH
04/28/22	Turnagain	Observation: More Turnagain Pass/Summit Lake wet slab activity	Alex Marienthal
04/27/22	Turnagain	Observation: Magnum	Sykes / Buttrick Forecaster
04/27/22	Turnagain	Observation: Girdwood/Summit/Turnagain Road obs	A S

Riding Areas

Updated Wed, June 01st, 2022

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 as of May 1 per Forest Plan.
Placer River	Closed	Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage	Closed	Closed as of April 1st per Forest Plan.
Turnagain Pass	Closed	Closed as of June 1st.
Twentymile	Closed	Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake	Closed	Closed as of May 1 per Forest Plan.
Lost Lake Trail	Closed	Closed as of May 1 per Forest Plan.
Primrose Trail	Closed	Closed as of May 1 per Forest Plan.
Resurrection Pass Trail	Closed	Closed as of May 1 per Forest Plan.
Snug Harbor	Closed	Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor	Closed	Closed as of May 1 per Forest Plan.
Summit Lake	Closed	Closed as of May 1 per Forest Plan.