Thu, January 30, 2020 Turnagain Pass Avalanche Forecast

Thu, January 30th, 2020

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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.

Avalanche Problem 1

Storm Slabs
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.

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

New snow is so exciting but the snowpack needs time to adjust to the snow load. There are now three storms worth of snow sitting on the weak snow (facets and surface hoar) that formed over the long stretch of cold and clear weather. With the previous storms that buried the weak snow, the snow had not formed a slab and the snow was enjoyed without incident. Yesterday there were some storm ingredients that may have changed all that and increased the likelihood of triggering a large avalanche. Because of the additional snow, warming temperatures and sustained strong winds, 2-3′ thick slabs now sit over the buried weak layers just waiting for a trigger. This set-up must be guilty until proven innocent. Be on the lookout for signs of instability today. Have there been recent avalanches? There were some naturals observed yesterday. Are there shooting cracks from your skis or machine? An observer yesterday noted cracks shooting out 3 ft. Can you feel collapsing? Does the snow feel grabby or punchy (a sign of heavier snow over soft snow)? Can you see drifting and cornices? Is the snow wind effected? Slabs over facets and buried surface hoar also have the potential to be triggered remotely. What slopes are you traveling on and under? If you or your party gets stuck in the snow in avalanche terrain, don’t send another to dig out. The message today is choose your travel route carefully and be conservative. Don’t let the powder cloud your judgement! Today could be a good day to check out the snow at Alyeska or enjoy the powder in the Placer or Turnagain flats!

Loose snow avalanches: Observers yesterday noted deep snow, getting stuck and overall slow going. In areas where the snow remains protected and soft, loose snow avalanches are possible in steep terrain. These could be quite hazardous in terrain traps. Even a small avalanche could bury you deeply.

The snowpack at 2500′ on Tincan, 1.28.20. There is now another 1-2′ of snow on top of the buried weak layers. This is the concern today.

A closer look at the buried surface hoar. This delicate weak layer has the potential to be triggered and cause a large, dangerous avalanche today.

Powder cloud from a natural avalanche observed at 2 pm yesterday from the Johnson Pass South trailhead. Recent avalanches are an indication that the snowpack is unstable. 1.29.20. Photo: Alex McLain

Weather

Thu, January 30th, 2020

Yesterday: Snow fell throughout most of the day with showers continuing overnight with 5-10″ of accumulation. Easterly winds ramped up in the late afternoon blowing 20-30 mph and gusting into the 60s and 70s. Temperatures were in the teens to start and then rose into the 20Fs.

Today: Mostly cloudy skies with snow showers with the potential for a few inches of snow. Easterly winds will remain elevated this morning 10-20 mph with gusts into the 30s and become light this afternoon. Temperatures will be in the teens and low 20Fs. Skies remain cloudy overnight with light snow showers, light winds and temperatures dip back down to the single digits.

Tomorrow: Scattered snow showers, mostly cloudy skies, light north winds and temperatures in the low teens. The cooling trend continues into Saturday and then temperatures warm again as the pattern changes into early next week. Stay tuned!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	21	5	.3	63
Summit Lake (1400′)	18	3	.1	21
Alyeska Mid (1700′)	21	9	.7	55

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	14	NE	23	73
Seattle Ridge (2400′)	18	E	10	34

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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