Issued: Fri, Dec 08, 2017 at 8AM

Expires: Fri, Dec 08, 2017

Above 2,500ft High

1,500 to 2,500ft High

Below 1,500ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

Problem #1: Storm Snow

Above the rainline (roughly 3,500ft), heavy snow has been falling over the last 1-2 days. South winds are strong, heavily loading North-ish aspects. Natural and human-triggered avalanches are likely within the new snow on slopes steeper than 30 degrees, especially areas with fresh wind loading. Storm slabs could be 60+cm thick.

Problem #2: Wet Avalanches

Location: all aspects below 3,500ft where rain has fallen on snow in the last 24 hours. A wet snowpack will exist in lower elevation areas, with natural and human-triggered wet loose and wet slab avalanches likely in steep terrain. Avoid all steep terrain where it has been raining. Gullies and chutes with steep terrain above will channel debris and funnel it into terrain traps. Some slides will reach lower runout zones.

Problem #3: Deep Slab

Beneath the midpack lurks a hidden danger. There is a persistent layer of 2-4mm depth hoar at the ground. The likelihood of triggering this weak layer will depend on how deep the snowpack is in a given location. Thin or rocky areas, especially at higher elevations, may act as trigger points. Remote triggering is possible and this weak layer is present on nearly all slopes above 1,500ft. Any failures this deep will propagate widely with deadly consequences. A few natural avalanches may break down to the ground as well, especially on North aspects. It would be wise to avoid lower runout zones of large, north-facing avalanche chutes. 

Recent Avalanche Activity

Observations on Thursday found widespread natural wet slab and wet-loose avalanches on East-North-West aspects around 3,500ft and below. Mostly size D3, with one D4. These wet slides were ripping out to the ground or to the ice crust just above ground. No observations from above the rainline due to limited visibility.

Recent Weather

Heavy rain will fall as high as 3,500ft Friday as the atmospheric river aims right at us. Expect more of the same for Saturday.

 Snow Depth [in] Last 24-hr Snow/SWE [in] Last 3-days Snow/SWE [in]  Today’s Freezing Level [ft]  Today’s Winds Next 24-hr Snow/SWE
Mount Ripinsky @ treeline
24″ 0″ / 0.10 7″ / 1.20 3700  str, S  0″ / 2.30 *
Flower Mountain @ treeline
 22″  0″ / 0.50  6″ / 1.50 3500 str, S  0″ / 1.70 *
Chilkat Pass @ 3,500ft
 23″ * 3″ / 0.50 * 15″ / 1.90 * 3500 str, S  6″ / 1.00 *

( *star means meteorological estimate )

Additional Info & Media

A few notes:

  • We had an extremely dry, cold early-season. Total precipitation October 1st – November 28th was around 30% of normal. Snow depths are between 45-130cm in most areas.  Variability is high due to persistent dry, windy conditions.
  • Temperatures hovered around 0 – 15°F for almost all of November. This has caused faceting of the thin snowpack and built up 3-5mm depth hoar at the ground in all zones. This will be a weak base to hold up future heavy snows. Keep this in mind as snow depths increase. This will likely turn into a deep-persistent slab problem.

If you get out on the snow, send in your observations!


We will be providing an AIARE Avalanche Level 1 Class this winter in Haines, February 23-25, 2018

More info and signup here.

 

Posted in Lutak Forecasts.
Erik Stevens

Forecaster: Erik Stevens