Sun, April 22, 2018 Turnagain Pass Avalanche Forecast

Sun, April 22nd, 2018

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 (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

Another spring storm is impacting Western Prince William Sound. Heavy precipitation has been seen in the Portage Pass zone and along coastal areas, with moderate amounts of precipitation in Girdwood and Turnagain. The storm is expected to intensify today and bring another 6-12″ of snow to the Alpine and .5-1″ of rain to Treeline and below. The rain/snow line is around 1,500′ this morning and should climb to 2,500′ by this afternoon.

Estimated Storm Totals from yesterday through 6am today (Sunday):

Girdwood Valley: ~6-10+” snow above 2,500′
Portage Valley: ~16″ – 24″ snow above 2,500′ (twice as much precip seen in areas closest to the Sound compared to Turnagain/Girdwood)
Turnagain Pass: ~6-10″ snow above 2,500′
Summit Lake: 0″ to a trace

Some natural avalanche activity is expected today if the storm verifies due simply to ‘rapid loading’. In the Alpine there could be up to 2′ of snow in favored areas by this afternoon. In this case, storm slab and wind slab avalanches are likely to be triggered. Although bonding between the new and older snow surface should be relatively good, there is always a period of time needed for the new snow to stabilize. This could happen in several hours or 2 days. Quick hand pits are good ways to assess instability in the storm snow. Once again the avalanche danger will be directly related to the amount of new snow fallen. In areas seeing only 6″(ish) of new snow, slab avalanches are not expected.

Upper elevation North aspects: Shaded aspects in the Alpine had a thin layer of facets over a crust under last week’s new snow. This layer may still be lurking, which could result in slab avalanches 1-2+’ thick composed of last week’s new snow along with this weekend’s storm.

A brief period of sun yesterday at Turnagain Pass. New moist snow falling on a warm springtime surface should bond fairly quickly after the initial stabilization period. However, once it warms up – avalanche activity will be on the rise again.

–

Avalanche Problem 2

Wet Loose
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Likelihood of Avalanches

Size of Avalanches

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

At the mid-elevations (below 2,500′) rain falling on a wet snowpack will keep the chances for natural wet loose avalanches possible on steep slopes. Make sure to avoid runout paths and gullies where even a small wet loose slide can send debris to valley floors. Triggering a wet avalanche will be likely if you find yourself on a steep slope with wet and unconsolidated snow.

Yesterday’s pre-storm snow surface and snowpack conditions at the mid-elevations. Rain at this elevation today will likely keep the snowpack punchy and wet, which means ripe for wet avalanches if the slopes are steep enough (greater than 35 degrees).

–

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Snow and wind continue to grow cornices along ridgelines. Cornice falls may trigger storm slab avalanches and/or wet loose avalanches today and looking ahead into the next several days of precipitation and warm temperatures. Give these a wide berth from above and limit exposure under them.

Weather

Sun, April 22nd, 2018

Mostly cloudy skies were over the region yesterday as another low-pressure system moved in. Light snow began to fall in the afternoon above 1,000′ and light rain below, the exception being heavy rain in the Portage area. Overnight, this first wave of the storm has added 5-12″ of moist snow above ~1,500′ and .5-1″ of rain below with Portage Valley seeing up to 2″ of rain at sea level. Ridgetop winds have been Easterly in the 20-30mph range. Temperatures along ridgelines have stayed in the 20’sF, while at 1,000′ sit in the mid 30’sF after warming to near 40F yesterday.

Today, Sunday, rain and snow will continue as this system looks to peak today. Another .5-1″ of rain is expected to fall below 2,500′ with 5-12″ of snow above this. Portage, and coastal zones, should continue to see twice as much precipitation as the Turnagain/Girdwood areas. Ridgetop winds will stay strong, in the 20-35mph range from the East. Temperatures also will remain in the 20’sF along ridgelines and in the mid 30’s at 1,000′.

For Monday, a break in the storm is expected before another round moves in Tuesday. Cloudy skies, light precipitation with a rain/snow line around 2,000-2,500′ and moderate Easterly winds should be seen Monday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	35	6	0.5	69
Summit Lake (1400′)	35	trace rain	trace	20
Alyeska Mid (1700′)	34	~4	0.5	61

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	NE	20	50
Seattle Ridge (2400′)	29	ESE	18	46

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.