Issued: Sun, Feb 25, 2018 at 9AM

Expires: Sun, Feb 25, 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 Moderate

1,500 to 2,500ft Moderate

Below 1,500ft Low

Degrees of Avalanche Danger ?

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

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

Skiing is getting good again, with about 8″ of excellent new snow on top of the old hard-pack. Beneath, 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: Wind Slab

Location: SW-S-SE aspects, and especially cross-loaded terrain features/gullies at all elevations. Yesterday’s new snow fell in moderate north winds, loading up alpine southerly aspects with fresh wind slab 15-60cm thick. This fresh slab is sitting on weak facets and a hard bed surfaceHuman triggered slides will be possible on slopes 28 degrees and steeper, and likely in any wind loaded areas.

Test slopes, hand shears, and quick pits will be useful tools to evaluate this danger. Stick to areas where the top layer of snow is protected from the winds and not forming a cohesive slab. Always practice good travel techniques, utilizing safe zones and escape routes, only exposing one person at a time to slopes over 30 degrees.

Problem #2: Persistent Slab

Trend: danger slowly increasing. Location: all aspects above 1500ft. Likelihood of triggering: possible. Confidence: low. Below the upper rain crust, recent cold weather has been faceting (weakening) the layers in the midpack and at the ground in thin, windswept areas. We’re getting occasional 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. Be aware that you may be able to trigger pockets of deeper slab, and surface avalanches may step down to these facet layers. Use extra caution in thin areas, and carefully evaluate the presence of this potential danger on steep slopes, and especially on unsupported slopes.

Recent Avalanche Activity

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

Sunday will be a nice break between storms. The next storm will come in Monday with heavy snow and strong south winds. 4-8″ is likely by Tuesday morning, with at least a few more inches possible Tuesday. It looks like a transition to 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
46″ 6″ / 0.40 8″ / 0.60 0  light, NW 0″/ 0.00 *
Flower Mountain @ treeline
 37″ 3″ / 0.20 8″ / 0.60 0 light, NW 0″/ 0.00 *
Chilkat Pass @ 3,500ft
 25″* 4″ / 0.30 * 8″ / 0.60 * 0 light, NW 0″/ 0.00 *

( *star means meteorological estimate )

Additional Info & Media

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 Transitional Zone Forecasts.
Erik Stevens

Forecaster: Erik Stevens