Fri, December 09, 2022 Turnagain Pass Avalanche Forecast

Fri, December 9th, 2022

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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

Yesterday we saw multiple small to large natural avalanches near the south end of Turnagain Pass (more info here). Most of these were partially filled in by new and blowing snow, but look to have occurred during the tail end or immediately after the Tuesday/Wednesday storm. Most of this activity was on terrain that had been wind-loaded, and they looked like they only involved new snow. The larger ones were big enough to bury a person.

Natural wind slab avalanche on the front side of Seattle Ridge, just up from the Bertha Creek parking campground near the south end of the ridge. Photo: Peter Wadsworth. 12.08.2022

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

The northwest winds are going to pick up today before dying down later tonight, and it’s looking like they are going to get strong enough to impact more of Turnagain Pass. Weather stations have been showing sustained speeds around 10-15 mph with gusts of 25-30 mph at Turnagain Pass– including the Sunburst station, which tends to be sheltered from these northwest winds. Our core forecast zone has been relatively protected for the past few days, with speeds around 25-40 mph for most of the day in Summit yesterday, and the AKRR mile 43 station showing gusts as high as 97 mph yesterday morning. We are expecting to see sustained speeds around 20-30 mph in the Turnagain Pass area today. Long story short, it is likely we will be able to find reactive wind slabs today, especially in the mid and upper elevations.

These fresh wind slabs are forming on top of a layer of facets in a lot of terrain, which will make them especially sensitive initially, and will most likely keep them reactive a little longer than your typical wind slab. The best way to stay out of trouble today is by avoiding wind-loaded terrain. The most dangerous slopes will be just below ridgelines, in steep gullies, and on convex rollovers. These northwest winds tend to load terrain differently than our more common easterly winds, so be on the lookout for fresh wind slabs in unusual areas. You should be able to find generally safer conditions (and higher quality snow) in terrain that has been sheltered from the winds.

If these outflow winds end up missing Turnagain Pass again, conditions won’t be quite as dangerous. You should be able to assess winds from a distance by looking for plumes of snow blowing off ridgelines. It is easy to identify wind slabs up close as you travel by stepping off the skin track and feeling for dense, stiff snow on top of softer snow. You can also use small test slopes to see how the new snow is behaving. Just be sure to use slopes that couldn’t produce an avalanche big enough to bury or injure someone.

Checking out a recent avalanche on the north side of Cornbiscuit. This avalanche was fairly small, but there was enough debris piled up in the gully below it to easily bury a person. Photo: Peter Wadsworth. 12.08.2022

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Weather

Fri, December 9th, 2022

Yesterday: Skies were mostly sunny, with temperatures slowly dropping from the mid 20’s to the mid teens F. There were strong northwest winds around much of the larger area, but Turnagain Pass and Girdwood stayed relatively calm, with sustained speeds of 5-15 mph and gusts of 25-30 mph. Compare this to the Mile 43 weather station, which had sustained speeds of 25-45 mph and gusts as high as 97 mph.

Today: Winds are expected to increase today for our core forecast area, with sustained speeds of 20-30 mph and gusts of 30-50 mph. Winds should be strongest later this morning, but are expected to continue through the day before calming down later tonight. Temperatures will continue their slow decline today, with highs in the single digits to low teens F, dropping to the single digits above and below 0 F tonight. Skies will be mostly sunny and no precipitation is expected.

Tomorrow: Things begin to change once again tomorrow. Cloud cover will increase as winds shift back to the southeast at 5-10 mph. High temperatures will be in the single digits to mid teens F, and no precipitation is expected during the day. It is looking like a proper storm is on the way for Sunday and Monday.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	17	30
Summit Lake (1400′)	18	21
Alyeska Mid (1700′)	17	29
Bear Valley (132′)	25	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	7	WNW	10	30
Seattle Ridge (2400′)	14	NW	10	25

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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