Wed, January 29, 2020 Turnagain Pass Avalanche Forecast

Wed, January 29th, 2020

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Conservative travel is recommended today. The likelihood of triggering a large slab avalanche in steep terrain is increasing. There is weak snow that formed during the long cold, clear period. This is now buried 1-2′ deep and will be even deeper after the storm today. The snow that fell Monday triggered a few small avalanches but was still mostly light, soft and not acting quite acting like a slab. That may all change today. Four to eight inches of snow has fallen since yesterday morning, it is snowing now and there is more snow in the forecast. The temperatures are rising so the snow will be heavier and strong winds starting this afternoon could quickly add weight. Snowpack tests yesterday showed the potential for the buried facets and surface hoar to become reactive with more of a load. As the slab develops over the weak snow avalanches could become large and may even be triggered remotely. Pay attention to both how steep the slopes are that you are traveling on are and what’s above you. When the winds increase this afternoon the potential for natural avalanches and cornice falls will also increase. Look for cracking and collapsing (whumpfs), both signs that the snowpack is unstable and choose terrain very carefully. Don’t be the trigger that tips the balance! The snowfall today will be heavier than yesterday creating an upside-down snowpack. This may act as a slab on it’s own and an avalanche triggered in the upper snowpack may step down to the lower weak layers.

Loose snow avalanches: On steep slopes where the slab hasn’t developed loose snow avalanches (sluffs) both natural and human triggered may occur. There is now both old soft snow and new soft snow that may easily move and be quite pushy. This is another good reason to choose terrain carefully.

Snowpack test at 2500′ on Tincan yesterday failed on the weak snow below the MLK jr storm snow. More load is expected on top today.

Turnagain Pass snowfall this morning. More snow load is being added to the snowpack with buried weak layers.

Video link HERE.

Weather

Wed, January 29th, 2020

Yesterday: Skies were mostly cloudy with a quick mid-morning clearing. Light snow started up again in the afternoon with 4-8″ of accumulation. Winds were easterly 5-15 mph with gusts into the 30s. Temperatures ranged from below zero into the low teens with a slow rise during the day. Overnight at most locations temperatures continued to rise into the high teens. Winds were easterly and snowfall continued, favoring Turnagain Pass.

Today: Snow to sea level will continue and may be heavy at times. Portage to Turnagain Pass will be continued to be favored by this system with another 10-15″ in the forecast. Winds will be easterly 10-25 mph with gusts into the 30s. Winds will increase in the afternoon becoming 25-40 mph with gusts into the 60s. A Blizzard Warning in effect from 3pm today until 4 am tomorrow. Temperatures will be in the mid teens to high 20Fs.

Tomorrow: Snow showers are likely with temperatures in the teens. Temperatures will drop back into the single digits by the evening. Winds are forecast to decrease in the early morning but remain easterly.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	11	8	.8	60
Summit Lake (1400′)	7	2	.2	18
Alyeska Mid (1700′)	11	5	.2	50

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	7	NE	13	33
Seattle Ridge (2400′)	11	E	4	15

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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