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Skies are clear. Under the tightening noose of a building ridge of high pressure, mountain temperatures are now at 24 hour highs in the mid teens. Gusty northerly winds continue to move snow and damage the open exposed terrain. They're still blowing 20-25mph with gusts to 30. 11,000' anemometers spin 35 mph with gusts to 50. Out of the wind and sun-zippered terrain, riding conditions remain superb, though a bit slow, on the recrystallizing snow surface and 1-2mm surface hoar from Thursday night.
Required Reading: Week in Review by Greg Gagne
Wow. A prolonged period of storms began late in the day on Friday Jan 20th, with an overachieving storm on Saturday the 21st with numerous human-triggered as well as natural avalanches occurring over the weekend. (Mark Staples described the activity of the weekend of Jan 21/22.)
Strong winds and heavy snowfall led to an avalanche warning issued by the UAC on Monday and Tuesday January 23/24 for the mountains of northern Utah. Little Cottonwood Canyon was closed beginning on Monday morning due to dangerous avalanche activity, and did not re-open until later Tuesday morning. Results from highway control work on several mountain roads in northern Utah produced large avalanches, with many hitting the road. A couple of Wasatch veterans reminded me that this is how "it used to be."
Throughout this extended period numerous natural and human triggered avalanches were reported on a variety of aspects and elevations, with several avalanches occurring at low elevations (< 9000'). Weaknesses included wind drifts, density changes within storm snow events, and persistent weak layers that formed during the spell of clear and cold weather from Jan 13 - 18, including both near-surface facets and surface hoar. Your pre-trip preparations should include reading field observations as well as recent avalanche activity from this past week. Bottom line - it was snowing and blowing for over a week, with storm snow falling on top of a weak, pre-existing snow surface at the mid and lower elevations, and it has led to a variable and complex snowpack.
Approximate storm and water totals since Jan 20 include:
LCC/BCC 80" 5.7"
Park City 44" 3.5"
Ogden 50" 2.5" - 3.5"
Provo 24" 2"
Requires a three part answer: persistent slabs, wind slabs, and minor wet loose point releases.
- Skiers triggered 6 separate persistent slabs 2-4' deep and generally 100' wide on north to east-southeast facing slopes yesterday. Elevations ranged from 7600'-9400'. This makes at least eight since Tuesday. All of these slides ran on either facets above a melt-freeze crust or surface hosr buried last Thursday January 19th under 50-90" of settling storm snow. Many of these slide were triggered remotely (at a distance) and caught and carried two skiers in separate events. The full list can be found here.
- With ramping north to northeast winds yesterday, a few sensitive natural and human triggered wind slabs occurred in high east to south facing terrain up to a foot deep.
- Minor wet loose point release sluffs peeled out of steep mid-elevation slopes with daytime heating.
Evelyn created a map depicting locations for these recent human triggered persistent slabs. Note these have been on many aspects below 9500' and predominantly along the northern periphery of the Cottonwoods (Park City ridgeline, Summit Park, Mount Aire). Note that a couple of the wind slabs are included on the activity rose on the right - these account for the upper elevation slides. On another note, I was blown away by the number of people who submitted reports and observations yesterday- your information saves lives. Thank you.