Mon, April 09, 2018 Turnagain Pass Avalanche Forecast

Mon, April 9th, 2018

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


Travel Advice	Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.	Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.	Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.	Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.	Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches	Natural and human-triggered avalanches unlikely.	Natural avalanches unlikely; human-triggered avalanches possible.	Natural avalanches possible; human-triggered avalanches likely.	Natural avalanches likely; human-triggered avalanches very likely.	Natural and human-triggered avalanches certain.
Avalanche Size and Distribution	Small avalanches in isolated areas or extreme terrain.	Small avalanches in specific areas; or large avalanches in isolated areas.	Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.	Large avalanches in many areas; or very large avalanches in specific areas.	Very large avalanches in many areas.

Avalanche Problem 1

Wet Loose
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

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

The sunshine that has been heating up the snowpack the past several days has been replaced with cloudy, warm and windy weather. Instead of cooling off and freezing overnight, the clouds have kept the heat in. This morning, temperatures sit near 40F below 1,500′ and much of the wet surface snow from yesterday has likely seen very little re-freeze. To add to this, light rain could fall up to 2,500′ today. Although the snowpack has been slow to undergo the springtime transition this year, the warm and cloudy weather today and tomorrow may start to push it over the edge. What this means is we could start seeing larger wet snow avalanches – something to keep in mind moving forward into the middle of April.

Wet loose avalanches: We have seen several small wet loose slides composed of last Wednesday’s storm snow over the past several days. Today, these are possible again and most likely in the mid-elevation band where the temperatures are warmer. Triggering one of these is possible on steep slopes with wet and saturated surface snow (East, West and South facing). The rule of thumb is, if you find yourself in saturated snow up to your boot tops, it’s time to head to lower slope angles or a different aspect with a drier snow surface.

Wet slab avalanches: We have not seen any wet slab avalanche activity, but it’s not out of the question a wet loose slide could trigger a wet slab today/tomorrow.

Recent wet loose avalanches on South facing Magnum Ridge (photo Allen Dahl).

Roller balls on Magnum’s Northerly face. These occurred yesterday and a sign Northerly aspects are beginning to warm. Roller balls are also a sign that wet loose avalanches are possible.

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Avalanche Problem 2

Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

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

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

Triggering a slab avalanche 1-2′ thick in the dry/moist snow on North shaded aspects is becoming more unlikely, but still possible. These slopes that harbored soft settled powder yesterday will become moister today. This change in surface character can add to instability in areas Wednesday’s storm snow has yet to bond well with the underlying surface. Most slopes are showing good bonding, yet we know there are areas with a facet/crust combination under the storm snow that keeps this concern in our minds.

Old storm slab on a Northerly aspect in Seattle Ck drainage (Main Bowl/1st Bowl) from last Thursday. Despite the initially poor bonding with the new/old snow last week, the snowpack was showing signs of good bonding now.

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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

It’s that time of year where the snowpack is slowly warming up and cornices will begin to break. We can’t let ourselves get complacent when traveling along ridgelines – give these guys a wide berth.

Large cornice that forms yearly over Zero (Momma’s) Bowl at the top of the up-track on Seattle Ridge. It’s easy to get lured into thinking we are over ground when in fact we may be over only snow and air.

–

Weather

Mon, April 9th, 2018

Partly cloudy skies were seen over the region yesterday before becoming mostly cloudy overnight. Ridgetop winds over the past 24-hours have been Easterly in the 10-15mph range. Temperatures rose to 50F below 1,000′ and up to the mid 30’sF along ridgetops. Overnight, clouds have kept temperatures warm and most elevations are reporting temperatures in the 30-40F range. No precipitation was recorded.

For today, a warm and windy day is on tap due to a low-pressure system in the Gulf ushering warm moist air our way. Light rain up to 2,000-2,500′ is expected with wet snow above this. Precipitation amounts expected are small, .2-.4″ of rain and 2-4″ of snow by tomorrow morning. Ridgetop winds will remain Easterly and increase to the 15-25mph range with stronger gusts. Temperatures will stay in the 40-50F range in valley bottoms and near 32F along ridgetops.

Tomorrow, Tuesday, continued cloudy, warm and windy weather will remain before the low-pressure system slowly moves South allowing cooler and possibly drier air for Wednesday into Thursday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	40	0	0	77
Summit Lake (1400′)	41	0	0	32
Alyeska Mid (1700′)	40	0	0	74

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	31	NE	12	34
Seattle Ridge (2400′)	35	SE	15	36

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S

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