Sat, December 10, 2016 Turnagain Pass Avalanche Forecast

Sat, December 10th, 2016

Alpine

Above 2,500'

1 - Low

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

Normal Caution

Normal Caution

Normal Caution means triggering an avalanche is unlikely but not impossible.

More info at Avalanche.org

It has been a week since we had any report of human triggered avalanche activity and observers are not reporting signs of instability. As a mostly calm, clear and cold weather pattern dominates our area and continues into next week, we are in the “normal caution” phase of avalanche issues. These include:

1- Triggering an outlier avalanche. This would most likely be an ‘unsupported slab’ that sits above a cliff or steep rocky terrain. More specifics below in the concerns.

2- Triggering a cornice fall. The cornices maybe be small right now, but they are large enough to take you down somewhere you don’t want to go. As always, give them a wide berth.

3- Sluffs on steep slopes. These have yet to have been observed as a problem but as the surface becomes weaker under clear skies the potential will increase.

Remember LOW hazard doesn’t mean NO hazard! It is still important to look for signs of instability and use good travel techniques.

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

Even with LOW avalanche danger it is still important to remember the weak layer 1-2′ below the surface i.e. the notorious Nov 16th buried surface hoar. Although we have not seen an avalanche release in this layer since last Saturday and the slab character has been changing due to the cold temperatures, there are many slopes away from the ‘popular’ zones that have yet to be tested. These are the areas most suspect over the weekend. Finding the spot that harbors this weak layer, still has a slab and hasn’t been skied or slid already still could be dangerous… Triggering is unlikely but not impossible!

Buried surface hoar in a pit on Sunburst, December 6th. SW, 3200′

Additional Concern

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

Several wind events over the last two weeks have formed wind slabs near and below ridgetops on a variety of aspects. Old stiff supportable wind slabs in thin rocky areas may pop once you are out onto the slab. Be wary of hard over soft snow, hollow sounds and steep slopes with obvious deposition in the start zone.

Weather

Sat, December 10th, 2016

Yesterday was mostly clear above the valley fog, which crept higher as the day progressed. Temperatures were in the low 20Fs and decreased through day. Winds were light and variable. Overnight temperatures dropped into single digits in the valleys and were in the teens up high. The wind speeds bumped into the teens gusting into the high 20s from the east.

Today will be cold and clear with light easterly winds shifting to north in the afternoon. Tonight and tomorrow look very similar with temperatures getting colder through the weekend. Single digits to mid teens should be expected. This weather pattern dominates into next week. Look for a potential shift with warmer temperatures and a chance of precipitation later in the coming week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	19	0	0	21
Summit Lake (1400′)	13	0	0	4
Alyeska Mid (1700′)	22	0	0	11

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	18	variable	7	27
Seattle Ridge (2400′)	21	variable	6	25

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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