Issued: Thu, Mar 08, 2018 at 8AM

Expires: Thu, Mar 08, 2018

Avalanche danger will be high to borderline extreme Friday. With three-day snow totals expected to reach 24″ at the Pass and 36″ near town, extreme danger is possible Saturday-Sunday.

Above 2,500ft Considerable

1,500 to 2,500ft Considerable

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

Bottom line: A layer of weak facets buried underneath last week’s new snow (about 15-40cm deep) is still active and touchy. Widespread danger signs exist, including whumphing and skier-triggered slides over the last few days. Wind loaded slopes steeper than 30 degrees are still quite dangerous, even in the trees (see photos below).

Problem #1: Persistent Slab

Location: All aspects and cross-loaded gullies, above 1500ft. With the strong southwest winds last week, followed by northerly outflow winds, we have areas of thick recent slab deposits on a variety of aspects. These slabs are hard and hollow above treeline, and softer in the trees, with weak 3-4mm buried surface facets underneath. Due to the nature of the weak layers and the continued cold weather, bonding is poor, and collapsing is common. Remote triggering has been a common report. These slabs could be anywhere from 15-60cm thick, and will be sensitive to human triggering on slopes steeper than 30 degrees. 

Resist the temptation to try out big terrain. We have not had a stabilizing event to reduce these surface instabilities, and we have not had enough time or warm weather to bond the weak layers.

We now have a “loaded gun” type of scenario where wind loaded slopes are stressed and waiting for a trigger.

Remote triggering and wide propagation will be possible, leading to large avalanches. Surface avalanches may step down to deeper facet layers 45-60+cm deep, below the upper ice crust.

 

Recent Avalanche Activity

In the last week, lots of whumphing, shooting cracks, and slide activity has been reported (failing on facets above and below the upper ice crust).

Several slides have been occurring in the trees around 2500-3500ft, on any aspect where the recent snow has loaded up. Photo below is the result from a ski cut. [ SS-ARc-D2-R2-O, E aspect at 3500ft, 40 degree slope, crown 30-45cm deep ] ran on 3mm facets above the ice crust. Lutak Zone, 3/4/2018.

There has been sporadic natural wind slab activity to size 3 in the Lutak and Transitional zones, mostly on wind loaded south aspects over the last week (see photo 1 below). In a few heavily-cross loaded areas around 4000ft, natural slides broke below the ice crust on persistent facets (photo 2 below).

Recent Weather

Thursday will bring a break between storms, with some clearing of the clouds. A strong storm will hit around midnight Thursday night with heavy snow and gusty south winds over ridge tops. 6-12″ of new accumulation is likely by Friday evening (lower amounts at the Pass). Continued snowfall is likely through Sunday.

 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
55″ 12″ / 0.80 12″ / 0.80 0  light, S 9″/ 0.80 *
Flower Mountain @ treeline
 40″ 6″ / 0.40 6″ / 0.40 0 light, S 6″/ 0.50 *
Chilkat Pass @ 3,500ft
 20″* 3″ / 0.20 * 3″ / 0.20 * 0 light, SE 4″/ 0.30 *

( *star means meteorological estimate )

Additional Info & Media

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

Posted in Chilkat Pass Forecasts.
Erik Stevens

Forecaster: Erik Stevens