Issued: Mon, Dec 18, 2017 at 8AM

Expires: Wed, Dec 20, 2017

Above 2,500ft None

1,500 to 2,500ft None

Below 1,500ft None

Degrees of Avalanche Danger ?

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

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

Problem #1: Wind Slab

After a wet and wild two weeks that have seen heavy precipitation and strong southerly winds, lingering wind slabs will be a concern for the days to come. Look for wind slabs at mid to upper elevations and all aspects of the compass, especially as the northerly winds pick up over the next few days, redistributing snow back to southerly aspects. Wind slabs are often smooth and rounded, and sound hollow when walked upon. Wind slab avalanches are likely in all lee terrain. These avalanches could fail on old snow interfaces or crusts within the snowpack and could be surprisingly deep.

Problem #2: Deep Slab

Despite the warm temperatures and copious precipitation, we can’t rule out the possibility that some stubborn depth hoar remains buried near the ground. Depth hoar is most likely to be found at upper elevations on North facing terrain. The last two weeks have added a tremendous load to this fragile layer and anywhere it still exists, it may be reactive. Look for depth hoar near the ground before committing to alpine terrain steeper than 30 degrees. Human triggered avalanches releasing at the ground remain possible.

 

 

Recent Avalanche Activity

Observations on last 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

The next few days will bring cooler and drier weather out of the North. An upper level ridge will build over central Alaska that will produce northerly gales over the Lynn Canal. This pattern should weaken on Thursday when a series of weak fronts bring some much needed precipitation back into the forecast.

 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
18″ * Tr” / 0.1 * 8″ / 0.7 * 0  mod, NW 1.0″/ 0.1 *
Flower Mountain @ treeline
 24″  0″ / 0.0  6″ / 0.5 0 lt, W  Tr” / 0.05 *
Chilkat Pass @ 3,500ft
 18″ * 0″ / 0.0 * 4″ / 0.3 * 0 mod, NW  0″ / 0.0 *

( *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 Chilkat Pass Forecasts.

Forecaster: Jonny Bomber