Sat, March 09, 2019 Turnagain Pass Avalanche Forecast

Sat, March 9th, 2019

Alpine
Above 2,500'

High (4)

Treeline
1,000'-2,500'

High (4)

Below Treeline
Below 1,000'

Considerable (3)

Alpine Above 2,500'		High (4)
Treeline 1,000'-2,500'		High (4)
Below Treeline Below 1,000'		Considerable (3)

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Avalanche Problem 1

Storm Slabs
Almost 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

It’s a simple equation: new snow falling on a slippery surface + wind loading = easily triggered avalanches.

Heads up for anyone headed out today. Storm snow avalanches are expected to be easily triggered. These will be in the form of wind slabs on wind loaded slopes, storm slabs in areas out of the wind, cornice falls and new snow sluffs. The size of the avalanche will depend on the amount of new snow and wind loading. In the Girdwood Valley slabs could be up to 3′ thick on wind loaded slopes. In the Turnagain Pass area, slabs could be up to 2′ thick. Come tomorrow, add another 10-20″ to the thickness of these slabs.

Although hidden from view, under the storm snow is the old surface, which is a combination of sun and wind crusts, facets and surface hoar. Not only will this old surface inhibit bonding with the new snow, it may also allow slabs to propagate wider than expected. Remotely triggered avalanches are also possible, meaning triggering a slide from the ridge or the bottom of a slope. With another round of snow and wind slated to hit later today, pushing the danger to HIGH, now is the time for us to keep out of avalanche terrain and let the mountains do their thing.

Estimated storm totals (mid-upper elevations) beginning Thursday ending Saturday 6am:

Turnagain Pass: 10″ – 16″ snow (1″ water)
Girdwood Valley: 16 – 24″ snow (1.5 – 2.3″ water)
Summit Lake: 1-2″ snow (0 – 0.1 water)
Bear Valley (Portage): 20 – 30″ snow (2 – 2.5″ water)
Seward area: 12″ – 20″ snow (1-1.5″ water)

Rain has been falling below 1,000′ and expected to continue today. This whas saturated the low elevations and wet sluffs will be possible.

Storm slab avalanche in the Tincan Trees from yesterday. Roughly 6 more inches of snow has fallen with more on the way, which will create much larger slabs for today. Photo: Allen Dahl.

The photo above shows the 6-8″ of new snow from yesterday sliding easily on the old sun crust that was the surface a few days ago. (Photo: Allen Dahl)

Weather

Sat, March 9th, 2019

Yesterday: Light to heavy snowfall was over the region as the second storm front passed through. Rain fell up to 500′ and in some areas up to 1,000′. Snowfall amounts across the region varied greatly from only a trace in the Summit Lake area to over 2 feet in the upper Girdwood and Portage Valleys. Turnagain Pass has seen around a foot of new snow. Ridgetop winds over the past 24-hours have been blowing 20-30mph from the east with stronger gusts. Temperatures have been steady in the low to mid 20’sF along ridgelines and in the mid 30’sF near sea level.

Today: A brief break between storms is expected this morning with the third wave of precipitation moving in midday and peaking late tonight. An additional 3-6″ of snow is expected to fall today with 10-14″ tonight. The snow/rain line should creep up to 1,500′ in areas and therefore, rain will be falling at the low elevations. Ridgetop winds are forecast to remain easterly in the 20-30mph range with gusts up to 50mph. Temperatures may reach the upper 40F at sea level, 32 at the mid elevations and the mid 20’sF along ridgelines.

Tomorrow: Stormy weather will continue Sunday and into Monday with an additional 6-12″ of snow at the mid and upper elevations. Cooler air looks to be entrained on Monday, which will lower the rain line and snow could fall near sea level. Another small break in storms may occur Tuesday before another round of precipitation hits. Stay tuned!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	10	0.8	63
Summit Lake (1400′)	33	trace	0	26
Alyeska Mid (1700′)	30	14	1.05	67

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	NE	29	57
Seattle Ridge (2400′)	27	SE	14	27

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/22/23	Turnagain	Avalanche: Tincan	Nick D'Alessio
05/12/23	Turnagain	Avalanche: Tincan, Sunburst, Magnum, Cornbiscuit	Heather Thamm
05/07/23	Turnagain	Observation: Tincan – Bear Tracks	CNFAIC Staff
05/05/23	Turnagain	Observation: Seattle Ridge	AS/ WW Forecaster
05/02/23	Turnagain	Observation: Cornbiscuit	Schauer/ Sturgess Forecaster
05/02/23	Turnagain	Observation: Seward Hwy Turnagain Pass	Joel Curtis
04/30/23	Turnagain	Observation: Magnum	Ayla, Kit Crosby, Barton
04/29/23	Turnagain	Observation: Tincan	John Sykes
04/28/23	Turnagain	Avalanche: Taylor Pass/Pastoral	Schauer/ Creighton Forecaster
04/28/23	Turnagain	Avalanche: Tincan	Andy Moderow

Riding Areas

Updated Sat, September 23rd, 2023

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area	Status	Weather & Riding Conditions
Glacier District
Johnson Pass	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Placer River	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Skookum Drainage	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Turnagain Pass	Closed	Scheduled opening on the Wednesday before Thanksgiving per Chugach National Forest plan. Subject to adequate snow cover.
Twentymile	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Seward District
Carter Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Lost Lake Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Primrose Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Resurrection Pass Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Snug Harbor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
South Fork Snow River Corridor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Summit Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.