|Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
|Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
|Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.
|Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
|Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
|Likelihood of Avalanches
|Natural and human-triggered avalanches unlikely.
|Natural avalanches unlikely; human-triggered avalanches possible.
|Natural avalanches possible; human-triggered avalanches likely.
|Natural avalanches likely; human-triggered avalanches very likely.
|Natural and human-triggered avalanches certain.
|Avalanche Size and Distribution
|Small avalanches in isolated areas or extreme terrain.
|Small avalanches in specific areas; or large avalanches in isolated areas.
|Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.
|Large avalanches in many areas; or very large avalanches in specific areas.
|Very large avalanches in many areas.
It was another sunny, cold and windy day yesterday. Plumes and flagging were evident along almost every ridge in the mountains at one point or another. The peak in winds occurred later in the day and this is expected to be the case again today as the Northwest winds are slated to bump back up to averages in the 20-30mph. Believe it or not, a few riders/skiers were able to find some soft snow in sheltered zones. However, much of the snow surface out there consists of wind hardened snow – sastrugi, wind slabs and wind crusts with scoured zones in between.
Wind Slab Avalanches:
With winds such as these we can expect to see hard wind slabs forming on leeward slopes. Additionally, cross-loading lower on slopes should be expected. Although a portion of the snow is being blown into the atmosphere, and not landing back on the surface, there is enough snow that is. Keep in mind, slabs could break above you and even a small hard slab can knock a person off their feet or snowmachine. Situational awareness is your friend. What slopes are being loaded by winds? What direction are the plumes going? With the relentless loading for days now, natural wind slabs could occur at the higher elevations and wash debris through gullies to wind protected zones that could ‘feel’ safe from below. Look for hollow feeling snow (stiff snow over soft snow).
These unpredictable hazards can release naturally and break farther back onto a ridge than expected. They also have the potential to trigger an avalanche on the slope below. Cornices should be given extra space above and below them.
Plumes along Seattle Ridge seen from the motorized parking lot.
Plumes on ridgetops looking South across Turnagain Arm from the Tesoro station in Girdwood.
Magnum’s West face is still somewhat saved from the winds as of yesterday afternoon. The winds have yet to destroy parts of Turnagain Pass on the East side of the highway.
Earlier this week when the ‘wind event’ first began, slopes loaded by winds reactivated older buried weak layers. In particular the February 9th buried surface hoar on the southern end of the advisory area (i.e., Johnson Pass and Summit Lake). This layer has been found to be shallower (12 – 20” deep), making it easier to trigger. In areas with a deeper overall snowpack (Seattle ridge, Tin Can, Sunburst, Girdwood Valley) the Feb 9th buried surface hoar is 2’-3’ below the surface and has been very tough to trigger in stability tests, but does continue to show the potential to fail and propagate.
The other weak layers are facets near the ground and in the mid-pack in some locations. This is a Deep Persistent Slab issue. Areas of concern include Summit Lake, Johnson Pass zone and some areas in Girdwood Valley. Continual winds with this event may be loading these old weak layers to the point of failure as well as be creating more trigger spots – thinner areas of the slab through scouring.
Photo below from the Summit Lake area. This avalanche likely occurred three days ago on Monday night or Tuesday morning. An example of a wind loaded slope that reactivated old weak layers near the ground.
Yesterday was yet another cold and windy day. The skies were sunny, but only in very protected spots from the wind did it feel warmer. Temperatures were in the teens at sea level and cooled with elevation to the single digits along the ridgelines. Ridgetop winds were from the Northwest in the 10-30mph range with gusts to 50mph at the Seattle Ridge weather station.
Today will be much of the same: sunny, windy and cold. The strong Northwest winds slowed slightly last night, but are expected to pick back up today, averages of 20-30mph. Temperatures will again be in the single digits and minus single digits along the ridgelines while parking lots are a bit warmer, ~10F.
There is what is called an omega block over Alaska currently that is litteraly blocking the warmer and moister air to our South for reaching us. This pattern looks to stay with us at least till next week and possible through next weekend. Meaning little to no chance for snow for a while. Expect the weekend to have brilliant sunny skies, cold (minus single and double digits) temperatures and moderate to strong North/Northwest winds.
|Temp Avg (F)
|Snow Depth (in)
|Center Ridge (1880′)
|Summit Lake (1400′)
|Alyeska Mid (1700′)
|Temp Avg (F)
|Wind Avg (mph)
|Wind Gust (mph)
|Seattle Ridge (2400′)
|Observation: Kickstep NE Bowl
|Observation: TinCan Backdoor/ Center Ridge
|AAS L1 Turnagain
|Avalanche: Lynx Creek
|Observation: Turnagain, Seattle, Mt Ascension
|Silverton Mountain Guides
|Observation: Tincan Trees
|Dalpes/Thamm/ Schauer Forecaster
|Observation: Seward Highway across from Johnson Pass TH
|Avalanche: Base of Seattle Ridge
|Troy Tempel, Thomas Lees, .Josh Bollaert, Damian Naquin
|Observation: Lynx creek