Sun, December 18, 2022 Turnagain Pass Avalanche Forecast

Sun, December 18th, 2022

Alpine

Above 2,500'

2 - Moderate

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 did not hear of any avalanche activity in our forecast zone yesterday. The last known avalanches were from early Thursday morning after the last snowfall/wind. Pictured below are some of the larger slabs that likely released around this time on Lipps and Pete’s North, photographed yesterday.

Large slab on the west face of Lipps ridge that appears to have broke in weak snow near the Thanksgiving crust. Andy Moderow 12.17.22.

Several avalanches on the SW face of Pete’s North. One has especially wide propagation, indicative of an avalanche breaking in a buried weak layer rather than just a storm slab avalanche. Andy Moderow, 12.17.22.

Avalanche Problem 1

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

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

Thank you for all the report-outs from people in the mountains yesterday! We heard of a few large ‘whumpfs’, but no avalanches. We also heard of folks that didn’t see any signs of instability. It is becoming clear however, that the weak faceted snow above and below the crust formed just before Thanksgiving is concerning in many areas; mostly in shallower areas such as the south end of Turnagain Pass, Lynx Ck, and Silvertip. Also, the Girdwood Valley has proven to be a problem spot as well. That said, with a few more clear sky days and easy travel, we still need to approach the slopes with extra caution. We are in one of those ‘scary’ MODERATE phases.

Hence, triggering a slab avalanche that breaks 1.5-3 feet deep is possible. This kind of avalanche could be triggered remotely, meaning from the bottom, sides, or on top of a slope. It could also release after several people have been on the slope. There may be NO signs of instability before an avalanche is triggered. This can set us up to think all may be fine until it is not. Good ways to manage this are to take extra care to travel one at a time in avalanche terrain, whether you are ascending or descending. Consider travel routes to limit exposure, always have escape routes planned, and watch your partners. Choosing lower angle slopes, 30 deg or less, can be a good way to just avoid the problem for those of us with lower risk thresholds. That said, if you hear a ‘whumpf’ that’s a problem and re-evaluating your plan, as several groups have done in the past few days, is prudent.

Weak faceted snow found above and below the Thanksgiving crust. This was around 2,300′ on a NE aspect in the Notch area of Girdwood Valley. The slab was around 2.5′ thick and composed of all the December storm snow. Ethan Tyler, 12.17.22.

Weather

Sun, December 18th, 2022

Yesterday: Cold and clear! Minus single digits in valley bottoms and teens to even 20F along the ridgelines due to an inversion in place. Ridgetop winds were light from the east to SE.

Today: Clear skies and cold temperatures will remain today. However, the inversion has weakened slightly with ridgelines remaining in the teens. Winds along the ridgetops should be calm to light from a northerly direction.

Tomorrow: Partly sunny skies, cold temperatures, and light easterly winds are expected through Tuesday. Clouds move in along with a chance for a few flurries on Wednesday. The next shot for decent snow amounts looks to be Friday into next weekend.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	18	39
Summit Lake (1400′)	-2	29
Alyeska Mid (1700′)	17	42
Bear Valley (132′)	-5	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	E	4	22
Seattle Ridge (2400′)	21	SE	4	10

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.