Fri, March 08, 2019 Turnagain Pass Avalanche Forecast

Fri, March 8th, 2019

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Considerable (3)

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

After two weeks of high pressure the jet stream has shifted and the first of two big storms is here. Overnight 1-3“ of snow fell, favoring Girdwood so far, and an additional 6-10” is expect today across the region. Strong Easterly ridgetop winds 30-40mph will continue all day. Sunburst has already seen gusts in the 50s mph. Temperatures have also risen and rain/snow line should reach 1000’ by mid-day. As snow and winds continue storm slabs and wind slabs will be growing in size. Monitor slab depths and avoid slope angles greater than 35 degrees. Leeward aspects could have deeper more connected slabs due to strong winds transporting snow. Also don’t forget about the weak surface conditions this new snow is falling on. Surface hoar and near surface facets are sitting on hard surfaces (sun crusts and wind-packed snow.) Basically this set-up does not bode well for future bonding. As we get more snow and wind this weekend and slabs grow thicker the avalanche hazard will continue to increase.

Wet Snow – Below 1000’ where rain is falling on dry snow on Northern aspects, triggering a loose-wet avalanche will be possible. In Portage Valley where precipitation amounts will be greater, natural avalanches are possible in steep channeled terrain and may entrain wet snow into the lower elevations. Avoid traveling on trails or terrain directly under steep avalanche paths.

South of Turnagain in the Summit Lake and Silvertip zones: Similar surface conditions to Turnagain Pass exist and any new snow that falls today is not expected to bond well. In addition a variety of old weak layers (facets and buried surface hoar) sit in the mid and base of the snowpack and wind loading and new snow will be adding more stress to these layers. Although less snow is expected to fall in this zone today keep in mind uncertainty exists for triggering a deeper more dangerous avalanche.

Surface hoar was present on all elevations and aspects prior to todays storm and was capped by a trace of new snow a few days ago.

Surface hoar sits on a sun crust on Southerly aspects (photo on left) and near surface facets exist on shaded aspects (photo on right.) In addition facets have been found under sun crusts and under thin wind slabs. We have plenty of weak surface snow issues to be concerned about.

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

These types of avalanches are highly unpredictable and not associated with human triggers. A number of cracks are located in popular terrain like Magnum’s SW face, Corn Biscuit, Lipps, and Repeat Offender on Seattle Ridge. The last glide avalanches to release naturally were a week ago on Seattle Ridge and in Girdwood Valley on Penguin, Goat, and Raggedtop. The best way to manage this problem is to watch for and limit exposure time under glide cracks.

On the left a glide avalanche released on Seattle Ridge on March 1st. On the right a glide crack continues to open on Repeat Offender. Photos courtesy of Allen Dahl.

Weather

Fri, March 8th, 2019

Yesterday: Skies were overcast. Easterly ridge top winds increased from light to moderate (15-25 mph) by the afternoon. Winds increased overnight with several gusts in the 50s mph this morning. Temperatures at ridge tops were in the low to mid-20s F and temperatures at sea level were in the mid-30s. Light flurries were observed late afternoon. Precipitation increased overnight and Alyeska midway station has seen 3 €œ new snow (.39″ SWE) and 1″ of new snow was recorded at Center Ridge. Temperatures at sea level this morning are 37F and rain is falling to ~500′.

Today: Stormy weather will continue today and overnight. An additional 6-10 €œ of new snow (~0.5 € SWE) is expected above 1000′ and will fall as rain at lower elevations. Portage will see higher precip totals due to its coastal location. Winds will be strong 30-40mph from the East with gusts in the 50s mph. Temperatures will increase throughout the day with a high of 40F at sea level. Rain/snow line could reach 1000′. Overnight another 4-8″ of snow (.43″ SWE) is possible.

Tomorrow: A second storm is tracking towards the Gulf of Alaska from the South and will arrive Saturday. This storm looks to have stronger winds, warmer temperatures and higher precip totals. Another 1-2′ of snow is expected in the upper elevations and rain below 1500′. Rain, snow and strong winds are expected to taper off Sunday afternoon.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	1	.1	57
Summit Lake (1400′)	31	0	0	27
Alyeska Mid (1700′)	31	3	.39	53

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	ENE	19	53
Seattle Ridge (2400′)	26	SE	14	32

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 Thu, June 01st, 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	Closed May 15.
Placer River	Closed	Closed May 15.
Skookum Drainage	Closed	Will close to motorized use on April 1, 2023 per the National Forest Plan.
Turnagain Pass	Closed	Will close on June 1.
Twentymile	Closed	Scheduled closure May 1.
Seward District
Carter Lake	Closed	Scheduled closure May 1.
Lost Lake Trail	Closed	Scheduled closure May 1.
Primrose Trail	Closed	Scheduled closure May 1.
Resurrection Pass Trail	Closed	Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor	Closed	Extended opening until May 15.
South Fork Snow River Corridor	Closed	Scheduled closure May 1.
Summit Lake	Closed	Scheduled closure May 1.