Fri, January 29, 2021 Turnagain Pass Avalanche Forecast

Fri, January 29th, 2021

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.

Avalanche Problem 1

Wind Slabs
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.

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 some hope that the low pressure in the Gulf would bring the mountains a foot of new snow today, that is turning out not to be the case… Instead, we are slated for 2-4″ of snow with moderate ridgetop easterly winds. The good news however, it remains cold enough for snow to sea level and those lakes and marshes are continuing to freeze up. That said, it’s another day where wind slab avalanches are the primary concern.

If you’re headed out, keep a lookout for any past or active signs of wind loading. Winds were blowing 15-20mph yesterday and lingering slabs may be found with or without fresh ones today. Watch for smooth rounded and pillowed snow surfaces, stiff snow over softer snow and any cracks that shoot out from your machine, board or skis. Quick hand pits are also a great way to assess wind slabs and if they want to slide easily (meaning they are unstable). Although new snow amounts are small, there is enough old loose snow available to be blown into fresh slabs. Add to this, wind slabs are likely to be sitting on loose faceted snow and buried surface hoar in places where the winds have not knocked it down. Exposed areas above the trees and in the Alpine are where this issue is most prevalent.

Loose snow avalanches (sluffs): On slopes out of the wind, expect a few inches of new snow over soft loose faceted snow. Skiers and riders have noted sluffs on steep sustained slopes increasing in volume over the past several days as the old surface has weakened with the chilly temperatures and clear skies.

Cornices: As you’ve seen recently on our reports, cornices are big and starting to peel away from ridgelines, creating cornice crevasses if they don’t break off. Just another mountain hazard to keep an eye on and another reason to give cornices a wide berth and limit time under them.

Photo of the surface hoar that sits over the loose faceted snow from a couple days ago. This is the old surface that is now being slowly covered by several inches of new snow. This set-up exists all the way to ridgetops. 1.26.21. Photo: Alex McLain.

Additional Concern

Glide Avalanches

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.

More info at Avalanche.org

Keep a lookout for glide cracks and avoid being under any of them. They have been releasing in a few areas around the region and we are beginning to notice some cracks open in areas that folks can easily travel below; on the road side of Seattle Ridge (across the parking lot) and on the Eddies, Tincan and Manitoba SW faces. These things are completely unpredictable and slide off in small chunks or large avalanches. It seems each clear day we see another crack or two, so we know they are on the move. Please shoot us a note if you see any!

Glide cracks on the South aspect of Manitoba in the Summit lake area. 1.28.21. Photo: Matti Silta.

Weather

Fri, January 29th, 2021

Yesterday: Mostly cloudy skies with a few snow showers were over the region. Between 2-3″ of new snow fell to sea level in Girdwood and extended to Turnagain Pass; only a trace to an inch fell in the Summit Lake area. Ridgetop winds were easterly in the 15-25mph range with gusts up to 40mph; winds have decreased overnight to 10-15mph. Temperatures were near 30F at sea level and in the teens along ridgelines.

Today: Cloudy skies and light to moderate snowfall, to sea level, is forecast during the day. Only 2-4″ of new snow is expected (.2″ water equivalent). Temperatures will be near 30F at sea level and the teens along ridgelines. Ridgetop winds will remain easterly in the 10-20mph range through tonight.

Tomorrow: Skies look to clear Saturday morning as high pressure builds over Southcentral. Winds will shift to a more north and northwesterly direction and usher in very cold air by Sunday. These winds look to remain light to moderate Saturday but may pick up by Sunday into Monday. Stay tuned.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	25	2-3	0.2	126
Summit Lake (1400′)	24	tr	tr	43
Alyeska Mid (1700′)	26	4	0.2	114

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	15	NE	15	40
Seattle Ridge (2400′)	19	SE	9	20

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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