Sat, April 22, 2017 Turnagain Pass Avalanche Forecast

Sat, April 22nd, 2017

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.

Avalanche Problem 1

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

After almost 2 weeks of sunny skies and high pressure, clouds and a warm East wind have moved in. The big news is how last night’s cloud cover has trapped yesterday’s daytime heat. This morning temperatures are 10-15 degrees F warmer than they have been during the past week and we are expecting a very limited, to no, re-freeze of the snow surface. The only thing that would help the re-freeze would be the increased winds, but they are only blowing 10-20mph and bringing in warm temperatures, so the wind may not keep the snow as cool as one would expect. That said, with a lack of re-freeze it will not take much daytime warming, or direct sunshine to initiate wet slab or wet loose avalanches.

WET SLAB, WET LOOSE, GLIDE AVALANCHES and CORNICE FALLS:
Although these are different characters of avalanches, they are all occuring together as the mountains fall apart with the springtime melt down. Widespread natural wet avalanche activity has already been seen on Southerly aspects, but the more shaded Westerly through Northeast aspects have yet to fall apart. This could happen this weekend as cloud cover has enhanced warming on all aspects. If choosing a day in the mountians this weekend be aware natural avalanches are possible and could become likely by Sunday. Things to keep in mind:

Did the snowpack re-freeze overnight in your location? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
Are you punching through a shallow crust into wet soggy snow? Also a sign the snowpack is weak and could avalanche.
Do you see any recent avalanches (take a look at the photo below to help identify a recent vs. an old avalanche).
Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down.
Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

Recent avalanche on Seattle Ridge (released Friday, April 21st)

Cloud cover over Tincan Ridge – trapping in the daytime heat overnight

*For the complete snow science geek out there – make sure and check out the Beaded Stream snow temperature array at the top of treeline on Tincan. This instrument measures ground, snow and air temperature vertically: Starting from 15cm (6″) below the ground, there is a cable extending 4meters (12′) upward that has a temperatures sensor every 15cm. The warmup of the whole snowpack can be seen – right now at this location (2,350′ in a flat area) the pack is almost isothermal , which means all the same temperaure at 32F. This is important because it indicates the potential for natural wet avalanches to begin on shady Northerly aspects.

Avalanche Problem 2

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

Although technically glide avalanches are a different beast than wet avalanches, they were lumped into the discussion above because how we deal with them now is similar to wet avalanches – simply avoidance. Avoid being under glide cracks – there are several cracks along Seattle Ridge, Tincan Ridge and many other slopes in the region. Each day we have seen 1-2 new glide releases (The photo above of Seattle Ridge being the last known glide release). The number of releases should increase with the warm weather.

Additional Concern

Deep Persistent Slabs

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

More info at Avalanche.org

Upper elevation Northerly aspects should be warmer today. The cold dry snow surface could be giving way to a moist and wet snow surface, if it didn’t already overnight. With the added warmth of the pack in these shaded zones, increased stress on underlying weak layers will be occurring. There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6′ deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. As the snowpack warms up, these weak layers could re-activate and triggering a large slab avalanche is possible. This is a low probability, high consequence problem.

Keep these points in mind:

It will take someone hitting a ‘thin spot’ in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall
There may be no signs of instability before the slope breaks
Several tracks may be on a slope before it releases
Stability tests may not produce any notable results

Weather

Sat, April 22nd, 2017

Cloudy skies (yes, cloudy for the first time in practically 2 weeks!) were over the region yesterday. Winds moved in with the clouds and over the past 24-hours ridgetops have been blowing 10-20mph with gusts in the 30’smph from the East. Temperatures warmed up to 50F at sea level, ~45F at 2,000′ and 30-35F along ridgetops yesterday. Overnight only a slight drop in temperature has been seen and all elevations.

Expect a cloudy, breezy and warm day today as we are on the Northern edge of a large trough digging in the Gulf to our South. Ridgetop winds should remain in the 10-20mph from the East while temperatures continue to be near 50F in the parking lots and 30-35F along ridgetops. There is a chance for a rain drop or two tonight, but most of the precipitation will be to the South near Seward.

For Sunday, we could see light rain in places as the frontal boundary associated with the Gulf trough sends some moisture our way. In general however, the forecast is for cloudy skies, warm temperatures and breezy winds.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	42	0	0	60
Summit Lake (1400′)	41	0	0	19
Alyeska Mid (1700′)	40	0	0	54

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	30	NE	38	16
Seattle Ridge (2400′)	33	SE	30	13

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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