Thu, December 20, 2018 Turnagain Pass Avalanche Forecast

Thu, December 20th, 2018

Alpine
Above 2,500'

High (4)

Treeline
1,000'-2,500'

High (4)

Below Treeline
Below 1,000'

High (4)

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

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

Today we recommend avoiding the backcountry due to HIGH avalanche danger. Heavy snow has been falling over the last 24 hours and is expected to continue through early afternoon. The estimated snowfall for Turnagain Pass is 4-5’ and more snow is expected through early afternoon. Snowfall rates have been in the 6”/hour (0.2 – 0.3” SWE/hr) overnight at the Turnagain Pass SNOTEL and 1-2”/hour in Portage and Girdwood. This is an unprecedented amount of snow in a very short period of time and natural avalanches could run far distances and very fast. Avoid all avalanche terrain including slopes steeper than 30 degrees and stay far away from any runout zones. In Portage Valley where channeled terrain runs to sea level avoid any trails with steep slopes above, like Byron Glacier trail. As an alternative to the backcountry, consider going to Alyeska!!! Santa’s ski for free today.

24-hour Precip:

Turnagain Pass SNOTEL: estimated 4-5 feet (3.4” SWE)
Portage Valley: 22” (1.03” SWE)
Girdwood – Alyeska Midway: 20” (1.04” SWE)
Summit Lake: 10” (0.4” SWE)

The snow stake at Turnagain Pass DOT lot shows ~ 3-4 feet of new snow in the last 24 hours.

Crowns from natural storm snow avalanches were seen yesterday in the Girdwood Valley at around 2500′. In this zone there was 13″ new snow mid-afternoon.

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

In thinner snowpack zones such as Summit Lake we are tracking buried layers of facets, crusts and buried surface hoar that sit 2-3′ under the snow surface. 10” of snow has fallen over night in Summit Lake and 6-12” is possible today. This new snow and moderate ridgetop winds may be adding more stress to an already weak snowpack. Triggering a slab near the ground is likely in avalanche terrain. The Lynx Creek and Johnson Pass zone have little to no snowpack data and often have a similar snowpack to Summit Lake. These zones are now open to snowmachining and this area likely received 2-3’ of snow in the last 24 hours. Today is not the day to push into Johnson and Lynx. HIGH avalanche danger is expected in this zone similar to Turnagain Pass.

Weather

Thu, December 20th, 2018

Yesterday: Heavy snowfall started around 8am and has continued through this morning. An estimated 4-5′ has fallen at Turnagain Pass (3.4 € SWE.) The Portage Rail Road Weather station is reporting 22 € at sea level (1.03 € SWE) and Alyeska midway is similar. Temperatures have remained in the mid to low 20F’s in the lower elevations and in the teens F at ridgetops. Ridgetop winds have been from the East 15- 30mph with some higher gust.

Today: A band of moisture and low pressure continue to pump snow through the Eastern Turnagain Arm region (North of Moose Pass to Girdwood.) The weather service has issued a winter storm warning with an additional 6-16″ is possible through early afternoon. Temperatures are expected to remain in the low 20F’s to low teens (F). Ridgetop winds will be light to moderate.

Tomorrow: An active weather pattern will continue tomorrow into the weekend with more snow showers in the forecast. Temperatures are expected to be in the 20F’s with light to moderate winds.

*Seattle Ridge weather station is rimed over and not recording any data.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	20	46″	3.4	85
Summit Lake (1400′)	16	10″	0.4	23
Alyeska Mid (1700′)	20	20″	1.04	40

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	13	ENE	14	37
Seattle Ridge (2400′)	*N/A	*N/A	*N/A	*N/A

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
12/10/19	Turnagain	Avalanche: Tincan and Sunburst from the air	CNFAIC Staff
12/10/19	Turnagain	Observation: Tincan	Nancy Pfeiffer
12/08/19	Turnagain	Avalanche: Tincan	Ryan Van Luit Forecaster
12/06/19	Turnagain	Avalanche: Sunburst	Billy Finley
12/04/19	Turnagain	Observation: Sunburst	A.Johnston-Bloom/ W.Wagner/ R.Van Luit Forecaster
12/03/19	Turnagain	Observation: Hippy Bowl	Nick Langowski
12/01/19	Turnagain	Observation: Tincan, All elevations	Eric Roberts
12/01/19	Turnagain	Observation: Tincan	Andy Moderow
11/30/19	Turnagain	Observation: Tincan Treeline Plateau/ Common Bowl/ Ridge	Eric Roberts
11/29/19	Turnagain	Observation: Sunburst Ob #2	Aleph Johnston-Bloom Forecaster

Riding Areas

Updated Wed, December 11th, 2019

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.
Placer River	Closed	Closed.
Skookum Drainage	Closed	Closed.
Turnagain Pass	Closed	Closed.
Twentymile	Closed	Closed.
Seward District
Carter Lake	Closed	Closed.
Lost Lake Trail	Closed	Closed.
Primrose Trail	Closed	Closed.
Resurrection Pass Trail	Closed	Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor	Closed	Closed.
South Fork Snow River Corridor	Closed	Closed.
Summit Lake	Closed	Closed.