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 Moderate
Degrees of Avalanche Danger ?
Snow totals in the Pass zone have been much less than near Haines, and variability is higher. Most areas in the Pass are still hard-packed and windswept, with gullies and wind loaded pockets holding soft snow. Today’s new snow should come in heavy, fast, and wetter than we’ve seen in a while. Any new snow will be falling over Saturday’s dry, low-density snowfall, which has formed soft slabs in windy alpine areas. 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, but especially cross-loaded terrain features/gullies. Today’s new snow will come in “upside-down” with rising temperatures and strong south winds. The wet snow will easily form soft slabs, and the dry, weak snow underneath will mean poor bonding and lots of settling. Natural avalanches will be likely today on steep, wind loaded NW-N-NE aspects and cross loaded gullies (Pockets of CONSIDERABLE danger). Human triggered soft slab avalanches will be possible on any slopes steeper than about 27 degrees, if the new snow piles up deeper than about 4″. 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: low. 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 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.
An intense but fast-moving storm will hit us Monday, with heavy snow and strong south winds. 3-7″ of new snow is likely by Tuesday morning, with at least a few more inches possible Tuesday-Tuesday night (Snow totals will be less at the Chilkat Pass). 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
|45″||0″ / 0.00||6″ / 0.40||0 -> 500||strong, S||7″/ 0.60 *|
Flower Mountain @ treeline
|36″||0″ / 0.00||3″ / 0.20||0 -> 500||strong, SE||4″/ 0.30 *|
Chilkat Pass @ 3,500ft
|18″*||0″ / 0.00 *||2″ / 0.20 *||0||strong, SE||2″/ 0.20 *|
( *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