Sun, December 20, 2020 Turnagain Pass Avalanche Forecast

Sun, December 20th, 2020

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 now been over a week since our last reported avalanches (more details here and here), and over two weeks since we have seen an avalanche big enough to bury a person. For the past week, we have gotten a steady trickle of low density snow with light winds, which is a great way to maintain quality riding conditions and improve stability. But, this doesn’t mean we can turn off our avalanche brains! For now, avalanches are unlikely, not impossible. Keep a few things in mind when you are out today:

Isolated wind slabs: There may be isolated pockets of wind loaded snow lurking below ridgetops and in cross-loaded gullies that could still fail today. Pay attention to warning signs like shooting cracks and whumpfing if you plan to move into steep terrain today.
Loose snow avalanches: Or, more commonly referred to as sluffs. Skiers near Magnum noted loose snow avalanches running long distances on Friday, and it will be possible to see more of the same today.
Cornices: As always, give cornices plenty of space, they often break back farther than you would expect.

If you are moving into steeper terrain today, be sure to only expose one person at a time to steep slopes, watch your partners from safe spots well out of the way of avalanche paths and runout zones, and be mindful of other groups traveling above and below you.

Although unlikely, it is not impossible to find isolated wind slabs like this one (which happened over a week ago) near ridge tops and in cross-loaded gullies. Eddies. Photo: Kakiko Ramos-Leon. 12.12.2020.

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

We know there is weak snow at the base of the snowpack throughout the advisory area, but it is quite variable and has shown signs of gaining strength. With no activity in this layer in over two weeks, very few signs indicating instability, and no significant loading in over a week, it is becoming very unlikely to trigger an avalanche deep in the snowpack. This layer is more concerning in areas with thinner snowpack such as Crow Pass, and as you head south from Turnagain Pass (Lynx Creek, Silvertip) towards Summit Lake. This type of avalanche is tricky. Deeply buried weak layers can often lay dormant for weeks or longer without showing any signs of activity before somebody finds just the wrong spot to trigger one. If you want to avoid problem entirely, you can stay off steep, rocky, slopes over 35 degrees.

Weather

Sun, December 20th, 2020

Yesterday: The mountains received 2″ new snow at the weather stations, with higher totals at upper elevations. Light winds around 5-10 mph at the ridgetops shifted from easterly to westerly yesterday afternoon. Temperatures dropped through the day, with morning temperatures starting the day in the mid- 20’s F and dropping to the mid teens F at lower elevations and dropping from the high teens to low teens F at upper elevations.

Today: We are expecting another quiet day weather-wise, with no snow accumulation under mostly sunny skies and westerly winds blowing 5-10 mph at the ridgetops. Temperatures should remain cool, with highs in the mid teens F at upper elevations, and low 20’s at lower elevations, and lows tonight around 10 F at upper elevations and low teens at lower elevations.

Tomorrow: Easterly winds are expected to pick up to 20 mph at the ridgetops in the afternoon, along with an increasing chance for precipitation as the next storm moves in. High temperatures should be in the low 20’s F at upper elevations and mid-20’s at low elevations. The National Weather Service has issued a High Wind Watch and a Winter Storm Watch for Monday evening through Tuesday evening. Stay tuned as the next storm develops, it looks like things could get spicy!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	19	1	0.2	60
Summit Lake (1400′)	18	2	0.2	27
Alyeska Mid (1700′)	17	2	0.2	62

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	14	N	9	25
Seattle Ridge (2400′)	17	N	12	3

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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