Issued: Tue, Feb 27, 2018 at 8AM

Expires: Tue, Feb 27, 2018

Caution advised in glacier areas: this year’s alpine snowpack is thinner than normal and our glaciers are more likely to have thin snow bridges over crevasses.

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

The last 24 hours have brought 4-10″ of new snow, and strong south winds. It’s falling over Saturday’s dry, low-density snowfall, which formed soft slabs over a bed of weak facets . Beneath that, we have 2 – 3 different mid-pack ice crusts, with various faceted layers in between, and depth hoar at the ground in thin areas.

Problem #1: Storm Snow

Location: All aspects and elevations. The last 24 hours’ new snow is “upside-down” (cold and weak on the bottom; cohesive, heavy, and wet on top). Strong southwest winds caused heavy wind loading on NW-N-E aspects. Continuing snowfall and winds today will only exacerbate this problem. Natural avalanches will be likely today on wind loaded aspects and cross loaded gullies. Human triggered soft slab avalanches will be likely on any slopes steeper than about 27 degrees. The icy bed surface under the new snow will make for large and fast loose-snow avalanches as well. Stick to the trees today, or stay on low-angle slopes. Be mindful of steep openings in the trees which are often wind loaded and lead to terrain traps below.

Problem #2: Persistent Slab

Trend: danger increasing with the new load from fresh snow. Location: all aspects above 1500ft. Likelihood of triggering: possible. Confidence: moderate. Below the upper rain crust sits a thick layer of weak facets, another crust, then more weak facets. We continue to get reports of whumping within the facet layer below the upper ice crust, which shows that this upper ice crust is decomposing and getting weaker as a bridge. With the added stress from new snow on top, we’re beginning to enter a “loaded gun” type of scenario.

Be aware that you may be able to trigger pockets of deeper slab (30-90cm deep), and surface avalanches may step down to these facet layers. We may start seeing remote triggering and wide propagation on these layers as well.

Recent Avalanche Activity

In the last week, lots of whumphing has been reported (failing on facets beneath the upper ice crust), as well as shooting cracks within the recent snow.

In the last two weeks there has been small natural wind slab activity on wind loaded slopes, with crowns up to 25-50cm thick. This is occurring regularly in sync with wind events. Cross-loaded slopes have shown the most activity since the winds have shifted direction several times.

Recent Weather

Ocean-effect snow showers with embedded waves will be rotating onshore through Wednesday morning, likely producing a few bursts of heavy snow. An additional 3-6″ is possible by Wednesday morning (bringing storm totals to 7-15″). Snow totals Tuesday night could be much higher if a wave develops and moves in, which the weather models are hinting at. Expect a transition to cold, dry arctic outflow conditions after that. 

 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
48″ 9″ / 0.80 15″ / 1.20 0  mod, S 6″/ 0.50 *
Flower Mountain @ treeline
 39″ 6″ / 0.40 8″ / 0.60 0 mod, var 4″/ 0.30 *
Chilkat Pass @ 3,500ft
 22″* 4″ / 0.40 * 6″ / 0.50 * 0 mod, var 3″/ 0.20 *

( *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