Mon, February 18, 2019 Turnagain Pass Avalanche Forecast

Mon, February 18th, 2019

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Moderate (2)

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

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

Very Large

Large

Small

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

This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches

This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.

More info at Avalanche.org

Triggering a 1-2′ thick slab avalanche on slopes 35 degrees and steeper is likely today. Wind loaded slopes are the most suspect. Yesterday the advisory area saw steady snowfall with an additional 4-10″ of snow (favoring Girdwood) and easterly wind loading throughout the day. Sunburst saw gusts into the 80s and Max’s into the 60s. Observers noted cracking and small test slopes being easily triggered later in the day. Visibility made Alpine observations difficult. The strong winds eased off in the evening and there was a break in the snowfall. Snow started again early this morning and is forecast to continue today throughout the advisory area. The old wind harden snow surface from before the storm and Saturday’s low-density snow will make it tough for the new snow to stick right away. ‘Upside-down’ snow was noted by observers yesterday. Today look for recent avalanches, shooting cracks and listen for whumpfs or hollow sounding snow. Choose terrain carefully. Cornices may be quite tender and should avoided.

Storm slab triggered on Sunburst at 1300′, 2-17-19. Photo: Elliot Gaddy

Storm slabs triggered on Tincan later in the day, 2-17-19. Photo: Ray Koleser.

Avalanche Problem 2

Persistent Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic

Very Large

Large

Small

Size

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.

Likelihood of Avalanches

Size of Avalanches

More info at Avalanche.org

New snow and wind loading have the potential to add stress to underlying weak layers. As we have been hammering home for weeks, in Turnagain Pass roughly 1-3′ below the snow surface sits a layer of buried surface hoar. Periphery zones such as Summit Lake and Johnson Pass harbor a poor overall snowpack structure with a variety of weak layers. Although these persistent weak layers have not been reactive lately, additional load may start to tip the balance. It is good to keep in mind that triggering an avalanche today could to step down into old weak layers and initiate a larger more dangerous slide. This is more likely in Summit Lake and the central Kenai mountains.

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

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.

Weather

Mon, February 18th, 2019

Yesterday: Skies were obscured with snow falling throughout the day. Winds were easterly 20-40 mph gusting as high as 88 mph on Sunburst. Temperatures were in the 20Fs to mid 30Fs. Overnight skies were mostly cloudy and winds were easterly 5-15 mph gusting into the 20s.

Today: Mostly cloudy skies and snow showers, 3-8″ of snow forecast. Rain/snow line around 700′. Temperatures in the 20Fs to mid 30Fs. Winds will be southeasterly 5-15 mph with gusts into the 20s. Light snow showers continue overnight with temperatures cooling into the low 20Fs.

Tomorrow: Skies clearing in the early morning becoming mostly sunny. Winds shifting to the northwest and increasing to 20-30 mph with gusts into the 40s. Temperatures will be in the low to mid 20Fs. The next storm system is forecast to move into the area Wednesday afternoon.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	29	2	0.3	62
Summit Lake (1400′)	30	2	0.2	28
Alyeska Mid (1700′)	29	5	0.6	58

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	NE	20	88
Seattle Ridge (2400′)	25	E	13	38

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
01/19/20	Turnagain	Avalanche: south facing aspect on 3800ft bump just northeast of 4940	Anonymous
01/19/20	Turnagain	Avalanche: Cornbiscuit & Magnum	Allen Dahl
01/19/20	Turnagain	Observation: Eddie’s	Kakiko Ramos-Leon
01/18/20	Turnagain	Observation: Sunburst	Ryan Van Luit Forecaster
01/18/20	Turnagain	Avalanche: Sunburst	Eric Roberts
01/18/20	Turnagain	Avalanche: North end Tincan trees	Heather Johnson
01/17/20	Turnagain	Observation: Tincan	Allen Dahl
01/16/20	Turnagain	Observation: Lynx Creek	Wagner / Van Luit Forecaster
01/13/20	Turnagain	Observation: Tincan	Ryan Van Luit Forecaster
01/12/20	Turnagain	Observation: Magnum West face	Levi Oyster

Riding Areas

Updated Thu, January 09th, 2020

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	Open	Open to over snow travel on Friday 1/3.
Placer River	Open	Open as of Friday 1/10. Early season conditions exist. Please avoid riding on the Railroad tracks. It is illegal and dangerous.
Skookum Drainage	Open	Open as of Friday 1/10. Early season conditions exist in. Please avoid riding on the Railroad tracks. It is illegal and dangerous.
Turnagain Pass	Open	Open to over snow travel on Friday 1/3.
Twentymile	Closed	Closed.
Seward District
Carter Lake	Open	Open to over snow travel on Friday 1/3.
Lost Lake Trail	Closed	Closed.
Primrose Trail	Closed	Closed.
Resurrection Pass Trail	Open	Open to over snow travel on Friday 1/3.
Snug Harbor	Open	Open to over snow travel on Friday 1/3.
South Fork Snow River Corridor	Closed	Closed.
Summit Lake	Open	Open to over snow travel on Friday 1/3.