Fri, November 25, 2022 Turnagain Pass Avalanche Forecast

Fri, November 25th, 2022

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

1 - Low

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

The last known avalanche activity was at the end of Tuesday night’s storm that brought around a foot of new snow to Turnagain Pass. Avalanches were generally small sluffs with a few smaller wind slabs on steep wind loaded slopes.

Loose snow avalanches on the backside of Seattle Ridge (Main Bowl) that occurred at the tail end of Tuesday night’s storm. Photo taken yesterday, 11.24.22, by Andy Moderow.

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

Wind slab avalanches will be the main problem for the next few days. Beginning today, winds have shifted northwesterly and should pick up along the ridgelines into the 15-25mph range with stronger gusts by midday and into the 30-40mph range tomorrow. There is plenty of loose snow available for transport after a surprise foot of new snow fell a couple days ago with another 2-4″ from last night. Wind slabs could be anywhere from 1-2′ thick and could be touchy when they are freshly formed. Starting tonight and into tomorrow, natural wind slab avalanches could occur if the wind forecast verifies.

If you are headed out hoping skies will clear a bit, watch for the winds. As we know from the past, this flow direction can funnel winds from all directions at Turnagain and load slopes on various aspects. As always, keep an eye out for active wind loading, stiffer snow over softer snow and cracks that shoot out from you. Wind slabs, and even small human triggered sluffs, can run further than expected on steeper slopes as there is crust under the loose surface snow below 3,000′ or so.

Easterly winds blowing snow on Pastoral Peak yesterday, 11.14.22. Andy Moderow.

Avalanche Problem 2

Persistent 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

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.

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

At the higher elevations, above around 3,000′, we are watching the base of the snowpack where a layer of facets exist. These are the October facets that created many large avalanches several weeks ago now. Although snowpit tests are showing mixed results and we have not been seeing avalanches release on this layer for some time in our forecast area, it’s still worth keeping in mind. Especially since a large slab was seen north of Girdwood (in upper Glacier Creek and pictured below) which could have released on this layer.

Given the uncertainty, paying attention to any recent large avalanche activity, with crowns several feet deep, and other warning signs like whumpfing in the snowpack is prudent. The winds today and tomorrow could test this layer by loading high elevation slopes. Something for all of us to look for.

Large avalanche in upper Glacier Creek (north of Girdwood) seen from Seattle Ridge yesterday, 11.24.22 by Andy Moderow.

Weather

Fri, November 25th, 2022

Yesterday: Clear skies were over the region yesterday morning with high clouds moving in later in the day. Ridgetop winds picked up in the afternoon into the teens with gusts in the 20’s mph from the east. Overnight, a brief pulse of moisture dropped 2-4″ of snow across the forecast area and to sea level. Temperatures have been hovering in the 20’s F in the mid and upper elevations.

Today: Mostly cloudy skies with a few snow flurries are expected this morning with some clearing by the later afternoon. Ridgetop winds will be picking up from the northwest through the day blowing 15-25mph by this afternoon with stronger gusts. Temperatures will drop with the cold outflow winds into the teens and single digits by tonight.

Tomorrow: Mostly clear skies are forecast tomorrow, Saturday, with cold temperatures continuing to be ushered in by the strong northwest outflow winds. Some higher elevations could see winds up to 40mph with stronger gusts – stay tuned. The next chance for precipitation looks to be later this coming week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	2	0.2	24
Summit Lake (1400′)	22	4	0.4	15
Alyeska Mid (1700′)	28	3	0.3	21
Bear Valley – Portage (132′)	27	2	0.2	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	23	E	10	27
Seattle Ridge (2400′)	25	SE	6	12

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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