Sat, January 21, 2017 Turnagain Pass Avalanche Forecast

Sat, January 21st, 2017

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

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

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.

More info at Avalanche.org

Yesterday winds were moving snow, a few inches of snow fell overnight and more is in the forecast for today. Winds remain strong enough to load slopes. This wind direction is opposite of the wind event on Thursday so leeward slopes will also be opposite. Fresh wind slabs may form throughout the day and be sensitive to triggering. Steep, unsupported, leeward slopes and ridgeline starting zones will be most suspect. There may also be old stubborn wind slabs from previous loading. Be on the lookout for wind transporting snow and pillowed or drifted areas. Avoid places where the snow feels stiffer and more affected by winds and watch for cracking.

Wind transport on Seattle Ridge yesterday.

Cracking in wind affected snow on Tincan yesterday.

Avalanche Problem 2

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

The storm is forecasted to continue today but there is still some uncertainty about how much snow will fall and which sections of the avalanche advisory area will be favored. So far the winner is Summit Lake with 9″ overnight. Center Ridge Snotel has only received 2″ so far but expect the southern end of the Turnagain Pass towards Johnson to have higher snowfall amounts already. Turnagain Pass could receive anywhere from 4″ to over a foot today. If the upper amounts are received there is potential for storm slab avalanches in places where the new snow doesn’t bond to old snow surfaces. In addition to paying attention to new snow amounts watch for temperature changes within the storm. Warmer snow falling on colder snow can quickly make reactive slab conditions. New storm snow will also add to the potential for loose snow avalanches on steep slopes. Paying attention to changing conditions will be crucial today as the avalanche hazard could increase even at lower elevations if this storm produces.

Additional Concern

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

A variety of weak layers exist within the snowpack and vary across our region. Following the most recent snowstorm (1/13-1/16) most of the avalanche activity has been observed in the Girdwood Valley. This makes sense since this storm favored this area and left 2-3’ of snow. A handful of small, but deep (to the ground) avalanches were spotted in the alpine this week on Southern aspects of Penguin Ridge, Raggedtop, and Magpie. Summit Lake also had natural avalanches from the Thursday wind event running on weak faceted snow. As more snow falls today remember triggering even a smaller persistent slab could bury a person or take you for a very unfavorable ride over rocks. Pay attention to areas where you can feel weak (sugary) snow under a stiffer snow. If you see recent avalanche activity, experience shooting cracks, or “whumpfing” these are obvious clues that you should avoid steep slopes.

Weather

Sat, January 21st, 2017

Yesterday was mostly cloudy with a few snowflakes falling in the afternoon. Temperatures were in the high teens to low 20Fs, notably warmer than the previous few days. Winds were Easterly blowing 15-25 mph gusting into the 30s.

Overnight a front impacted the area favoring Summit Lake and south. Turnagain received a couple of inches and just inch fell in Girdwood. Snowfall is expected to continue throughout the day will an additional 4-7 inches possible. Winds will be from the SE 5-15 mph with gusts into the 20s. There is some convective potential with this system and overall uncertainty in total snowfall amounts. Temperatures will be in the teens into the mid 20Fs

Tonight snow showers may linger with another 2-4 inches and light E winds. Temperatures will be in the teens. Tomorrow the unsettled weather pattern continues as another system moves towards the region. Stay tuned for snow amounts and temperatures.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	16	2	.2	43
Summit Lake (1400′)	17	9	.9	24
Alyeska Mid (1700′)	18	1	.1	38

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	14	ENE-ESE	15	28
Seattle Ridge (2400′)	13	SE	22	35

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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