Sun, December 14, 2014 Turnagain Pass Avalanche Forecast

Sun, December 14th, 2014

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

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

Storm Slabs

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.

More info at Avalanche.org

A warm and very intense storm is arriving as we speak. The rain/snow line should rise to 2,000′ and 10-16″ of snow is forecast above 2,500′. Associated with the new snow will be very strong Easterly ridgetop winds. This is a classic storm snow avalanche problem. With wind likely to affect most locations above 2,500′, naturally occurring wind slab avalanches are expected on many leeward slopes. These are expected to run into the 2,000′ elevation zone, where it may be raining, and possibly further.

Not only is a foot or more of new snow falling in 12 hours, accompanied by strong winds, a concern in itself, it is falling on a very weak pre-existing surface. Widespread surface hoar up to the ridgetops – 2cm (3/4″) in size, which is significant – was just starting to be covered up intact and upright yesterday. Hence, bonding between the new snow and old snow will be poor with this persistent weak layer sandwiched in between. As snow piles up and becomes cohesive with the warm temperatures, slabs will have potential for wide propagation.

Slab depths for today’s expected new snow will be in the 1-2′ range. These are not exceedingly thick slabs for a HIGH danger day, but the expected rapid loading on a weak layer of surface hoar should produce widespread avalanche activity with dense debris. Steering clear of avalanche terrain while it continues to snow and blow is recommended.

Avalanche Problem 2

Wet Loose

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.

More info at Avalanche.org

Rain on an old battered and frozen snowpack is expected from ~2,000′ and below. Above this, around 2,500′, 6-8″ of wet snow is likely to fall on a stout and well developed crust. Naturally occurring wet loose avalanches composed of the new wet snow are likely to run on steep slopes. Areas that are in this zone are the East face of Seattle Ridge and Magnum’s West face.

Weather

Sun, December 14th, 2014

Yesterday, skies were mostly cloudy with light snow beginning to fall in the early afternoon as the leading edge of today’s low pressure system pushed in. The rain/snow line rose to 500′ by the evening. Don’t forget about the table below for additional past 24-hour weather details!

Overnight we have seen ~.3-.5 of rain below ~1000 in the Girdwood Valley and Portage area with 4″ of wet snow at the Center Ridge (Turnagain Pass) SNOTEL site at 1880′. Ridgetop Easterly winds are on the rise from the teens to the 30’smph with gusts to the 50’s. Temperatures are steadily climbing (unfortunately) with 1,000′ temperatures in the mid 30’sF.

Today, we will see temperatures rise another few degrees F with the rain/snow line creeping to 2,000′. Between 1 and 1.5″ of water equivalent is expected by this evening at Turnagain Pass with 10-15″ of snow at the above treeline elevations. Ridgetop Easterly winds are forecast to be in the 30-40mph range with stronger gusts.

Monday, precipitation, Easterly wind and even temperature should decrease slightly. Models are showing 1 – 1.5″ of rain below 1,500′ and another 10-16″ of snow above.

A series of low pressure systems will continue to move through the Northern Gulf with additional cooler temperatures and additional snow (hopefully to sea level). Stay tuned.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	4	0.4	22
Summit Lake (1400′)	28	0	0	4
Alyeska Mid (1700′)	32	2	0.6	15

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	E	21	54
Seattle Ridge (2400′)	27	SE	15	31

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/27/23	Turnagain	Avalanche: Tincan Ridge	Schauer/ Stiassny Forecaster
11/26/23	Turnagain	Observation: Road report: Slide with dirt on Repeat offender	Anonymous
11/26/23	Turnagain	Observation: Pete’s North	Ben Sullender
11/25/23	Turnagain	Observation: Tincan trees	John Sykes Forecaster
11/21/23		Observation: Spokane Creek	John Sykes Forecaster
11/20/23	Turnagain	Observation: Sunburst	Anonymous
11/19/23	Turnagain	Observation: Magnum – PMS Bowl	Schauer/ Cullen/ Jonas Forecaster
11/19/23	Other Regions	Observation: Sunnyside/Penguin	Jose Ramos-Leon
11/19/23	Turnagain	Observation: Eddies	Andy Moderow
11/19/23	Turnagain	Observation: Cornbiscuit	Anonymous

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