Issued: Thu, Dec 07, 2017 at 8AM

Expires: Thu, Dec 07, 2017

Above 2,500ft High

1,500 to 2,500ft High

Below 1,500ft Moderate

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 3500ft), heavy snow has been falling over the last 1-2 days. South winds are strong, heavily loading North-ish aspects. All this heavy, moist new snow is sitting atop weak low-density snow from the weekend. Human-triggered avalanches are likely on slopes steeper than 30 degrees, especially areas with fresh wind loading. The new/old snow interface will be a likely sliding surface. Storm slabs could be up to 60cm thick, leading to large avalanches.

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 human-triggered wet loose and wet slab avalanches likely in steep terrain. Avoid all steep terrain where it has been raining. 

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

SS-AR-D2-R3-S | A snowboarder-triggered D2, Nadahini-area, 10-28-2017

October 28th: First rider-triggered slide reported from the peak north of Nadahini (“Sunny Bunny”). D2 soft slab ran in storm snow from Oct 26-27. Nobody caught or injured. [ SS-AR-D2-R3-S ] South aspect @ 6,200ft.

Small – Moderate natural avalanche activity is occurring during/after storms. So far it has been mostly loose-snow slides, with a few slab avalanches as well.

Recent Weather

Rain will fall as high as 4000ft Wednesday night as the atmospheric river drifts overhead and a strong tropical wave moves in. Precip. amounts will be highest towards the Chilkat Pass.

 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″ / 0.50 7″ / 1.10 3600  str, S  0″ / 0.20 *
Flower Mountain @ treeline
 26″  0″ / 1.00  6″ / 1.80 3300 str, S  0″ / 0.40 *
Chilkat Pass @ 3,500ft
 16″ * 10″ / 1.50 * 15″ / 0.40 * 3300 str, S  4″ / 0.40 *

( *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 Transitional Zone Forecasts.
Erik Stevens

Forecaster: Erik Stevens