Issued: Sat, Mar 10, 2018 at 5PM

Expires: Sun, Mar 11, 2018

A large avalanche cycle is expected over the next 24-48 hours. All avalanche terrain and lower runout zones should be avoided.  Gullies and runout zones will channel wet debris and some slides may reach flat areas at the margins of runouts, and even the Haines highway in a few spots between 15-25 mile.

Above 2,500ft Extreme

1,500 to 2,500ft Extreme

Below 1,500ft High

Degrees of Avalanche Danger ?

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

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

Bottom line: Avoid all avalanche terrain today and this weekend. We’re in the middle of a large avalanche cycle.

Heavy precipitation, south winds, and a strong warming trend, followed by rain-on-snow below 3000ft, will lead to Extreme danger Saturday night and Sunday.

In the backcountry, remote triggering and wide propagation will be possible, leading to large avalanches. Surface avalanches may step down to deeper facet layers 45-100+cm deep, below the upper ice crust.

A layer of weak facets buried underneath last week’s new snow (about 50-100cm 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 above 1,500ft. With the strong southwest winds last week, followed by northerly outflow winds, we have areas of thick recent slab deposits under the new snow on all 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 45-100cm thick, and will be sensitive to human triggering on slopes steeper than 30 degrees. 

Even slopes that slid last week will have the potential to reload over these weak persistent facets and avalanche again.

Problem #2: Storm Snow

Location: All aspects and elevations, slopes 30 degrees and steeper. New snow totals from the last 3 days are around 13″ in the Transitional zone, and 24″ in the Lutak zone. Mountain winds have been moderate-strong out of the South, so expect wind slabs and loading on northerly aspects and cross-loaded terrain features. On any slope steeper than 30 degrees where the new snow is wind-affected and cohesive, you will be able to trigger soft slabs, as bonding is poor right now.

Problem #3: Wet Avalanches

Location: All slopes below 3,000ft, 30 degrees and steeper. As temperatures warm up Sunday and rain begins to fall below 3,000ft, dangerous wet slabs and wet sluffs will be common in steep terrain. Gullies and runout zones will channel wet debris and some slides may reach flat areas at the margins of runout zones, and even the Haines highway in a few spots between 15-25 mile.


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

A strong storm hit around midnight Thursday night with heavy snow and gusty south winds over ridge tops. 4-8″ of new snow fell (lower amounts at the Pass). Another 3-6″ fell Friday night. A strong burst of moisture will bring heavy snow and warming temperatures Saturday night, with an additional 8-16″ possible and snow levels rising to 2,500ft Sunday. Heavy precipitation will continue Sunday-Sunday night.

 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
59″ 6″ / 0.55 25″ / 1.95 0 -> 2500  light N   ->
strong S
18″/ 1.80 *
Flower Mountain @ treeline
 42″ 4″ / 0.35 13″ / 1.05 0 – > 2500 light N   ->
strong S
14″/ 1.40 *
Chilkat Pass @ 3,500ft
 22″* 3″ / 0.25 * 9″ / 0.70 * 0 – > 2500 light N    ->
strong S
11″/ 1.00 *

( *star means meteorological estimate )

Additional Info & Media

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

Posted in Transitional Zone Forecasts.
Erik Stevens

Forecaster: Erik Stevens