Thu, April 13, 2023 Turnagain Pass Avalanche Forecast

Thu, April 13th, 2023

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Moderate (2)

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

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Recent Avalanches

We saw multiple natural and human-triggered avalanches yesterday as the sun came out and warmed all of the storm snow that we’ve gotten this week. This includes a large avalanche near Johnson Pass/Bench Peak, which was up to 7′ deep and most likely only involved new and wind-loaded snow, a skier-triggered avalanche on Tincan’s Common Bowl, and a small snowmachine-triggered avalanche in the Placer Valley. We also saw many wet loose avalanches releasing as things heated up yesterday.

It’s a little misleading in the photo, but that crown in the background was actually up to 7′ deep. We believe it was a wind-loaded slope that only involved new snow. Photo submitted anonymously, 04.12.2023

Avalanche Problem 1

Storm Slabs
N E S W NW NE SE SW

Aspect/Elevation
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.

Aspect/Elevation of the Avalanche Problem

Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

Our main concern today will be triggering an avalanche failing at the interface between the new snow that we’ve gotten since Sunday and the older snow surface. We’ve found this new snow has been slow to bond to the older surfaces, and when the sun popped out yesterday we saw a handful of natural and human-triggered avalanches. With slightly cooler temperatures and cloudy skies today, that new snow should have some time to gain more strength and avalanches should be a little less likely today than they were yesterday. That said, there is still some uncertainty as to how quickly it is healing and steep terrain should still be approached carefully.

Be on the lookout for warning signs of unstable snow today. This can look like cracks shooting out from your skis or snowmachine, or fresh avalanche activity. This is the kind of problem where it may be informative to use small but steep terrain features to see how well the snow is bonding. It can also be very useful to take a few seconds to hop off your snowmachine or step off the skin track an dig down to the old snow surface with your hand to see how well the new snow is bonding. If you have any doubts about stability, you can avoid the problem entirely by just staying off steep slopes for now.

It is looking like the clouds should give us some relief from the warming we saw yesterday. We should see some sun poking through this morning, and if that sun hangs around longer than expected we need to be on the lookout for more wet loose activity if things heat up through the day. It is possible that a loose snow avalanche could pull out a bigger slab as it travels downhill, so be sure to pay attention to changing conditions through the day.

Skier-triggered avalanche in Tincan’s Common Bowl yesterday. Photo: Chris McNeil 04.12.2023

The new snow was not glued on well to the old snow surfaces in our snowpit yesterday. This was on a low-elevation south facing slope, with a stout crust below the new snow. Photo: Megan Guinn. 04.12.2023

Additional Concern

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

While our main concern lies in the new snow in the upper snowpack, we know there is a suspect layer buried deeper in the pack. This was responsible for many very large avalanches in the second half of March, but we have not seen any activity on it for the past two weeks. It seems this layer has gone dormant for now, but it is still something we are keeping in the back of our minds. The new snow from this week is adding a little stress to the snowpack, but it seems the layer is strong enough to support it. We’ll continue to track this layer, and our guard will be up as soon as we see a significant warming event or another big loading event.

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Weather

Thu, April 13th, 2023

Yesterday: Skies were partly cloudy to mostly sunny yesterday, with high temperatures reaching the upper 20’s to 40 F and lows in the high teens to upper 20’s F. Light snowfall in the first half of the day brought a trace of new snow. Winds were light at 5-10 mph with gusts of 10-20 mph out of the south.

Today: Skies will start out partly sunny, with clouds building through the day and a chance for some snow showers later in the afternoon. Winds will start out light out of the west before switching easterly at 5-10 mph with gusts of 10-20 mph. High temperatures should be in the upper 20’s to mid 30’s F, with overnight lows in the low to upper 20’s F.

Tomorrow: Snowfall continues tonight into tomorrow morning, with another 2-4” expected by midday tomorrow. Winds will pick up slightly out of the east at 10-20 mph with gusts of 15-25 mph. Skies should be mostly cloudy with high temperatures in the upper 20’s to mid 30’s F and lows in the mid to upper 20’s F.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	0	0	94
Summit Lake (1400′)	31	0	0	46
Alyeska Mid (1700′)	32	tr	tr	90
Bear Valley – Portage (132′)	33	0	0	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	S	6	22
Seattle Ridge (2400′)	26	S	3	9

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.