Issued: Mon, Mar 12, 2018 at 8AM

Expires: Mon, Mar 12, 2018

A large avalanche cycle is ongoing. 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. 36-hour storm snow totals are about 24″ in the Pass and Transitional zones, and 36″ in the Lutak zone.

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. We’re in the middle of a large avalanche cycle.

Extreme danger will continue Monday, due to increased warming and additional rain-on-snow. The last 36 hours have brought continuous heavy precipitation, strong south winds, and a strong warming trend, followed by rain-on-snow below 3000ft.

In the backcountry, remote triggering and wide propagation will be possible, leading to large avalanches. Surface avalanches may step down to deep facet layers 100-200cm deep.

A layer of weak facets buried underneath last week’s new snow (about 100cm deep) is still active and touchy. Widespread danger signs exist, including whumphing and skier-triggered slides over the last week. 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. About a meter down, we still have weak 3-4mm buried surface facets. This facet layer and ice crust underneath has caused many avalanches, and prolific collapsing over the last week. Remote triggering has been a common report. The slab on top could be anywhere from 80-150cm 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 2 days are around 24″ in the Pass and Transitional zones, and 36″ in the Lutak zone. Winds were moderate-strong out of the South yesterday, so expect wind slabs and loading on northerly aspects and cross-loaded terrain features. Human triggering will be likely within the storm snow on any slope steeper than 30 degrees where the new snow is wind-affected and cohesive.

Problem #3: Wet Avalanches

Location: All slopes below 3,000ft, 30 degrees and steeper. Rain is falling up to about 3,000ft today. 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

Very heavy snow and warming temperatures hit Saturday night-Sunday night, with 24-36″ of wet new snow above 1,000ft by Monday morning. Rain/snow will continue Monday, before finally tapering off Tuesday. Very warm air will move in Tuesday, with freezing levels rising to 5000ft at least. Luckily it won’t be raining during this time.

 Snow Depth [in] Last 24-hr Snow/SWE [in] Last 7-days Snow/SWE [in]  Today’s Freezing Level [ft]  Today’s Winds Next 24-hr Snow/SWE
Mount Ripinsky @ treeline
80″ 12″ / 1.20 56″ / 4.90 1500 -> 3500  light, var 5″/ 0.50 *
Flower Mountain @ treeline
 62″ 14″ / 1.20 37″ / 3.00 1000- > 3000 light, var 5″/ 0.50*
Chilkat Pass @ 3,500ft
 41″* 14″ / 1.20 * 33″ / 2.70 * 1000 – > 2000 light, var 4″/ 0.40 *

( *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