Good morning. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, February 6th at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
There are pockets of HIGH avalanche danger today for slab avalanches on lower elevation slopes were light rain has been falling on snow. Additionally, there is a CONSIDERABLE danger for unmanageable and deep wind slab avalanches at the mid and upper elevations. The snowpack is ripe for triggering dangerous slab avalanches at all elevations today – conservative travel in the backcountry is warranted – avoiding low elevation slopes and slopes steeper than 35 degrees at the mid and upper elevations is advised.
The avalanche danger is believed to have spiked to HIGH late in the day yesterday and overnight due to warm temperatures, high winds and light precipitation. Despite very limited visibility, we did see a few natural avalanches, with more likely shrouded in the clouds. One descent sized ‘damp’ slab released in the lower elevations near Peterson Creek. Estimated at 200′ wide, 3 feet deep, running 500′; a good example of how rain on cold snow can be a prime trigger – our situation right now at the lower elevations. There were also a couple medium size natural wind slab avalanches barely visible just above treeline in the Tincan area.
As far as human triggered avalanches go, these were the norm yesterday on steep wind loaded rollovers in the more ‘mellow’ treed terrain. They averaged 10-18″ deep and consisted of heavy dense wind deposited snow. Collapsing and shooting cracks were common and one party did remotely trigger one slab from their skin track. The high winds were able to reload slopes that already slid, causing them to repeat. Due to most folks only toying with the smaller rollovers, these did not pose a large threat, however, this type of avalanche in more committing terrain would be very dangerous and likely not manageable.
For today, the primary concerns will mirror the above avalanche problems from yesterday:
Lower elevations (below 1000′):
Slab avalanches triggered by continued rain on snow. Though rain has be light, conditions were becoming ripe for these to release naturally yesterday afternoon and may have undergone a natural cycle overnight. Regardless, steering clear of any slope at the lower elevations will be wise until the snowpack adjusts to the shock of the warm rain and the added load. We also know there are locations were a buried weakness exists adding to the likelihood of slides.
Mid and upper elevations:
Wind slab avalanches will again be likely to trigger today. These have, and are, only becoming larger and less manageable if they do slide; especially considering the nature of the heavy dense snow that make up the slab. Cornice breaks will also be likely today. The cracking and collapsing in the weaker snow which was certain yesterday is likely settling out today, but that does not mean they will not release, and in fact they may break deeper. Furthermore, new wind slabs forming today will likely take their place.
Last, a quick note to watch for roofs that are shedding their snow as well with these warm temperatures.
It was a wet and windy day in the backcountry yesterday. Around .3-.7″ of rain has fallen in the last 24 hours below 500′ with heavy snow above and becoming lighter with elevation. Mid elevations picked up around 3-5″ of dense snow in the Eastern Turnagain Arm with less in the Summit area. Winds were strong to gale force all day, blowing in the 50’s and gusting to almost 80mph from the east.
Today, expect warmer temperatures but with decreased winds and less precipitation. Light rain and snow showers should tapper off through the day. Temperatures have climbed overnight and are above 32F below 2500′ and in the upper 20’s to 30F on the peaks. Easterly winds had decreased a bit and are expected to be around 40mph on ridgetops.
The warm southeast flow is forecast to persist for the next several days, with decreasing precipitation today and clearing tomorrow. Wednesday looks like a shot for more substantial moisture.
CNFAIC Weather Page and the NWS forecast
Graham will issue the next advisory Tuesday morning. If you get out in the backcountry we want to know what you are seeing. Please send us your observations using the button at the top of this page or give us a call at 754-2369. Thanks and have a great day.