Mon, December 14, 2015 Turnagain Pass Avalanche Forecast

Mon, December 14th, 2015

Alpine

Above 2,500'

3 - Considerable

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.

Avalanche Problem 1

Storm Slabs

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.

More info at Avalanche.org

After a brief break in storms yesterday, another pulse of moisture added 5-6+” of new snow last night, with an additional 2-3″ expected today. It’s starting to look like winter up at the Pass! Yesterday also was the 1st time in over 18 months that enough snow covered the ground to allow the Chugach National Forest to open to motorized use. Many, many folks were out enjoying the day as well as testing the slope stability. After a good thumping by snowmachines, we only had one report of a sled triggered avalanche. This was remotely triggered in 2nd Bowl (Junior’s Bowl). If anyone has additional information regarding any other avalanche activity please send us a quick note HERE.

Avalanche conditions today will be mainly confined to storm snow issues. These are:

WIND SLABS: Strong winds blew from a generally East direction last night accompanying the snowfall. With the new snow plus plenty existing snow available for transport, watch for any slope that has been freshly wind loaded. These slabs are likely to be around a foot thick, but do have the potential to ‘step down’ into deeper layers and trigger a larger avalanche. Watch for cracks that shoot from your snowmachine/skis/board and areas with a smooth rounded surface texture – these are signs that a wind slab is present and could slide if the slope is steep enough.

SLUFFS: Sluffs on steep slopes should be expected within today’s light snow.

Again as Heather pointed out yesterday, the snowpack is dramatically thicker on the North end of the Turnagain Pass. With that said, the South side of the Pass is slowly filling in. Photo below is from Mike Records from the Silver Tip area:

The motorized lot on opening day 2015/16.

Avalanche Problem 2

Persistent Slabs

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.

More info at Avalanche.org

Under the 16-30″ of storm snow from the past 5 days sits both a layer of Buried Surface Hoar (BSH) and a layer of Near Surface Facets (NSF). Although one of these layers may be the culprit for the avalanche yesterday, we cannot say that for certain since we were not able to investigate. We do know stability tests are showing mixed results, with the general theme of no reactivity. Although it is becoming unlikely to trigger a large avalanche breaking 2+’ down, it is not out of the question and something to keep in the back of our heads.

A look at a layer of BSH at 3,100′ on a SW aspect – you can see the ‘thin gray’ line in the middle of the snow (Photo credit Andy Moderow, report HERE). This layer is not found everywhere and since it can be a problem layer for avalanche activity, we are tracking it.

Weather

Mon, December 14th, 2015

Yesterday afternoon skies clouded over, Easterly winds picked up and snow began to fall as a quick moving system rolled through. Between 5-6″ of snow fell overnight with Easterly winds averaging in the 30’s and 40’s mph. Temperatures have climbed slightly and are sitting near 20F on the ridgetops and near 30F at sea level.

Today, intermittent snow showers will linger with mostly cloudy skies. We may pick up an additional 2-3″ in favored areas. Winds have decreased this morning and will be in the 5-15mph range from the East.

Tuesday night through Thursday another round of snowfall is expected as a strong low-pressure moves into the gulf.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	23	5	0.4	41
Summit Lake (1400′)	21	2	0.2	14
Alyeska Mid (1700′)	24	6	0.42	35

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	17	NE	32	66
Seattle Ridge (2400′)	19	N/A	N/A	N/A

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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