Tue, December 15, 2015 Turnagain Pass Avalanche Forecast

Tue, December 15th, 2015

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.

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

Observations from yesterday are pointing toward an overall snowpack that continues to adjust to this latest pulse of snow. The weak snow above the Thanksgiving rain crust continues to show signs that it is gaining strength and didn’t prove to be a concern in our snowpits yesterday. Keep in mind this set up though (see secondary concern below) and recognize that areas where wind loading has occurred, there will be more weight on this weak snow/ storm snow interface. Large triggers such as a snowmachine could prove enough to tickle out a fresh storm slab or wind slab 2-3’ deep.

Skiers pushing into steeper, upper elevation terrain (above 3500’) may also find fresh wind slabs in the 2-3’ range as we had a short but strong wind event on Sunday night. In areas protected from the wind and lower elevations, the surface is quite unconsolidated. Generally with more snow on the northern end of Turnagain pass, loose snow sluffs will prove to be fast moving and high volume today, particularly in steep terrain (greater than 40 degrees).

CNFAIC forecasters are elated to be able to utilize snowmachines again as a forecasting tool after last winters “snow drought” at trailhead locations. Here, Graham Predeger digs in to look at our current snowpack structure at 2400′ above 2nd Bowl (Jr’s bowl) on the backside of Seattle ridge.

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

We will continue to track the Thanksgiving rain crust/ facet combo (and buried surface hoar layer) until it is buried more than 3 feet deep AND proves dormant. Though not reactive recently, all the ingredients are present to bake that cake (2’+ storm slab/ weak snow/ stout bed surface). For the moment, look at this avalanche problem as an additional reminder to maintain safe travel protocols, and ensure you and everyone in your crew is carrying proper rescue equipment and knows how to use it.

Weather

Tue, December 15th, 2015

Low-level fog persisted most of yesterday near sea level with broken clouds and partly sunny skies above about 500′. The snowfall shut off early yesterday morning with no new precipitation added during the daylight hours. Winds were calm (single digits) throughout the day and temps were in the 20’s from valley bottom to ridgetops.

Today, temperatures are starting out slightly inverted, promoting valley fog, though with a weak pulse of moisture arriving mid to late morning, that should usher in easterly winds in the 25-40mph range at ridgetops and act to mix the air a bit. We may see 1-3 € of snow falling from sea level and up, around the eastern Turnagain arm region with temperatures in the 20’s F at ridgetops and low to mid 30’s F at sea level.

More active weather is on tap through the workweek as another low pressure moves into the Gulf and begins to affect Kodiak as early as tomorrow.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	24	0	0	39
Summit Lake (1400′)	23	0	0	14
Alyeska Mid (1700′)	25	0	0	33

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	W	4	28
Seattle Ridge (2400′)	20	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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