Sun, December 31, 2023 Turnagain Pass Avalanche Forecast

Sun, December 31st, 2023

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

Mon, January 1st, 2024

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

Mon, January 1st, 2024

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


Travel Advice	Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.	Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.	Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.	Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.	Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches	Natural and human-triggered avalanches unlikely.	Natural avalanches unlikely; human-triggered avalanches possible.	Natural avalanches possible; human-triggered avalanches likely.	Natural avalanches likely; human-triggered avalanches very likely.	Natural and human-triggered avalanches certain.
Avalanche Size and Distribution	Small avalanches in isolated areas or extreme terrain.	Small avalanches in specific areas; or large avalanches in isolated areas.	Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.	Large avalanches in many areas; or very large avalanches in specific areas.	Very large avalanches in many areas.

Recent Avalanches

We saw continued glide activity yesterday, with fresh glide cracks and avalanches reported in Turnagain Pass and Summit Lake. This includes new glide cracks opening above heavily-traveled areas especially on Seattle Ridge.

Fresh glide avalanche on Wilson South. Photo taken by Eliot Pearce, 12.29.2023

New glide crack opening directly above the common uptrack from Main Bowl north into Junior’s. Photo: Troy Tempel, 12.30.2023

Avalanche Problem 1

Wind Slabs
N E S W NW NE SE SW

Aspect/Elevation
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.

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

After a week of clear, calm, and cold weather, a more active system has returned. Weather stations have been showing increasing easterly winds since yesterday evening, and we are expecting to see sustained speeds of 30-50 mph with gusts in the 60’s through today. Along with the strong winds we should see a few inches of new snow, with 2-4″ expected for most of the advisory area and closer to 8-10″ possible for the Portage and Placer valleys. This new snow and strong winds will once again draw our focus to avalanches failing where fresh wind slabs are forming.

The cold and clear weather over the past few days caused weak faceted snow and surface hoar to develop at the snow surface. Those weak surfaces are now getting buried by new and wind-drifted snow and will make for reactive conditions for the next few days. As the winds continue to load some slopes during the day today, we are expecting to see natural and human-triggered avalanches. These will become larger and more likely through the day as slopes continue to see wind loading. Since we are only looking at a few inches of new snow we are not expecting these avalanches to be huge, but they will be touchy. Expect to find unstable snow near ridgelines, below convexities, and in cross-loaded gullies today, and be aware of increasing danger as the active weather continues through the day. Look for better skiing and riding conditions, and more stable snow, on slopes that are sheltered from the winds.

Active weather has returned after a week of cold, clear, and calm conditions. Photo from the RWIS webcam at the Portage side of the Whittier tunnel this morning. 12.31.2023

Avalanche Problem 2

Glide Avalanches
N E S W NW NE SE SW

Aspect/Elevation
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.

Aspect/Elevation of the Avalanche Problem

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

We are continuing to see new glide cracks opening and releasing across the advisory area. While it is fairly common to see glide activity during midwinter cold snaps, this glide cycle has been noteworthy not only because of the extent of the activity, but also because of the alarming pattern of glide activity in high-traffic areas. Turnagain Pass seems to be the most active zone, but we have also observed very active cycles in Girdwood and Summit Lake. Seattle Ridge seems to be at the epicenter of all of the activity, with dozens of glide avalanches over the past week and gaping cracks currently open directly above commonly used uptracks on the front side and in the back bowls.

Glide avalanches are nothing to mess with. They are large, destructive, and impossible to predict for a given slope. The current cycle is way more active than normal, and that warrants extra caution. Pay close attention to the overhead hazard, and consider using alternate routes if the routes we commonly use are threatened by glide cracks above. These may look like a gaping brown frown if the cracks open all the way to the ground, or they may be a more subtle wrinkle if the crack is just opening up. If you can’t find another way around them, increase your margins of safety by limiting the time you spend below open cracks and only traveling one at a time when you need to cross under one.

Looking down at a recent glide avalanche on the front side of Seattle Ridge, just above the motorized parking lot. Photo: Graham Predeger, 12.30.2023

Closeup of a fresh glide crack opening right in the middle of Goldpan. 12.30.2023

Weather

Sun, December 31st, 2023

Yesterday: We saw another cold and clear day yesterday, with temperatures as cold as -15 F at road level in Summit Lake and the south end of Turnagain Pass in the morning. Temperatures have been rising since yesterday morning and are now in the mid teens to low 20’s F. Yesterday afternoon the weather station at the west end of the Whittier tunnel warmed 38 degrees in six hours! Winds were light out of the west for most of the day, switching to the east and increasing to 10-20 mph gusting to 30 mph along ridgetops since early last night. No precipitation was recorded.

Today: The easterly winds that began to increase last night will continue to ramp up through today, with average ridgetop speeds of 30-50 mph and gusts of 40-60 mph. Most of the area will see 2-4” snow today with another inch or two tonight, with rain lines slowly rising to around 500 feet tonight. As usual Portage and Placer are looking to receive more precipitation, with an expected 8-10” snow today and another 5-6” tonight. Temperatures should be in the high teens to low 20’s today, climbing to the mid 20’s to low 30’s tonight.

Tomorrow: Things are looking to calm down tomorrow, with some lingering snow showers bringing a trace of snow under mostly cloudy skies. Winds will remain out of the east, but calm down slightly to 15-30 mph with gusts of 25-35 mph. High temperatures will be in the mid 20’s F with lows in the high teens to low 20’s F.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	8	0	0	75
Summit Lake (1400′)	-1	0	0	N/A
Alyeska Mid (1700′)	11	0	0	67
Bear Valley – Portage (132′)	9	tr	0.03	–
Grouse Ck – Seward (700′)	3	1	0.1	49

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	11	W-E	9	31
Seattle Ridge (2400′)	11	NW-SE	9	19

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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