The Bottom Line: The hazard rating above treeline is Moderate. Triggering new wind slabs 1-3' is possible in steep terrain and triggering older deeper slab avalanches is unlikely but still possible.
Problem 1: Wind Slab
Distribution: All elevations exposed to north winds. Size: Small-Large. Likelihood: Possible. Sensitivity: Stubborn.
Description: 2+' of new snow fell between Feb 17-21 and was transported and hardened by 48+ hrs of strong northerly winds. New wind slabs formed up to 2' deep. These slabs are stubborn but could propagate wide due to the stiffness of the slab; they also have the potential to step-down into older persistent slabs below. The new snow and wind load needs time to settle and bond. Use caution in ALL avalanche terrain AND choose lower angle slopes, avoid terrain traps, and look for loaded slopes.
Problem 2: Persistent Slab
Distribution: All aspects above treeline. Size: Large-Very Large. Likelihood: Unlikely. Sensitivity: Stubborn.
Description: There is a widespread buried weak layer (surface hoar, buried Jan 23) that has 1-3' of slab on top of it. This is a low probability-high consequence setup. This layer is gaining strength; but this REAL problem still lingers: on Feb 15 a natural wind slab avalanche on Hippy Ridge stepped down and released on this layer (size D2.5). This weak layer is more prevalent and reactive the further north/interior you travel. Evaluate ALL avalanche terrain carefully, choose mellower terrain, AND consciously choose group spacing. If SNOW is the Question, Terrain is the Answer. This kind of avalanche problem is difficult to assess and may behave unpredictably.
Problem 3: Glide Avalanches.
There are open cracks from the port to 42-mile between 3500-4000' on multiple aspects. There have been multiple full releases near Girls Mtn and on the Deserted Glacier. It is important to remember glide cracks can release at any time and are not associated with human triggers. New snowfall is covering up these gaping, crevasse-like features so use caution particularly when traveling in FLAT LIGHT. The best way to manage this problem is to limit (AKA avoid) travel underneath and beside them.
The current list of known open glides cracks from West to East:
Feb 12: 2 small skier triggered wind slab avalanches were reported from the north side of Billy Mitchell. 2x SS-AS-D1 6" crown that 'propagated fairly wide.'
Please share your field observations including signs of stable snow HERE.
The most recent NWS rec Forecast can be found HERE:
300 AM AKST Sat Feb 23 2019
The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
Temp at 1000` 25 F 6-13 F
Temp at 3000` 13-23 F 24 F
Chance of precip 0% 0%
(above 1000 FT) 0.00 in 0.00 in
(above 1000 FT) 0 in 0 in
Snow level sea level sea level
Wind 3000` ridges NE 0-19 mph NE 1-19 mph
SNOWPACK BIG PICTURE: In the top 3' of the snowpack there is a challenging combination of weak layers and new wind slabs in the Valdez region. Below the Jan 23rd buried surface hoar the snow has good strength and structure. The further interior, the problem layers are more widespread and snowpack is considerably shallower.
Recent snowpack history, from top to bottom:
Feb 20-22: High N-NE winds, rapidly transporting any available snow (70mph gusts).
Feb 16-18: Over 2" SWE and 2' of snow with little wind.
Feb 7-14: Nearly 0" new snow and building north winds (70mph NE gusts on Feb 14 at Thompson Pass.) Widespread surface hoar growth up to 6mm. In windy locations, and close to the pass, most of this surface hoar has been knocked down. A 'drizzle crust' formed near the pass up to 5500' and was observed buried 55cm down on Loveland at 5000' (on Feb 20.)
Feb 3-6: 0.7" SWE and 8" of snow from Valdez to Thompson Pass. 8" of new snow was recorded at 5500' on Catcher's Mitt. Freezing level was sea level throughout this cycle.
Jan 30-Feb 1: Natural avalanche cycle on all aspects above 3000', up to size D3. Most ran on buried surface hoar.
Jan 28-30: 2" SWE in Valdez, moderate winds, freezing level 1000'.
Jan 23-25: Multiple days of warm and wet with periods of rain up to 2500'.
Jan 13-22: Mostly clear, cold, and dry with light to moderate north winds. Widespread Surface Hoar growth (up to 15mm) and Near Surface Faceting.
Jan 12-13: 3-10" of new snow with little wind.
Jan 4-12: was VERY cold and dry: moderate winds and wind chill reaching -50F. Pockets of surface hoar and widespread near surface faceting.
Dec 30-Jan 3: The New Year's Eve storm brought nearly 2.5" of SWE to Valdez and almost another 1" (SWE) on the 2-3rd of January. The rain line was 1200' during the Jan 2-3 storm, forming a 1-3" crust locking up all the snow beneath it. These storms accumulated over 3' above 2000' near Thompson Pass. Both of these storms had little wind.
Above 4000' the snowpack averages well over 300cm deep and has good strength and structure (few lemons). Below 4000', the snowpack is significantly shallower and has old problem layers that are bonding well (rounding) and currently dormant: facet-crust combos and BASEL facets (all the way to sea level).
If you get out riding, please send in an observation.
Do a rescue practice with your partners. Always carry a beacon, shovel, and probe, and KNOW HOW TO USE THEM.
Practice good risk management, which means only expose one person at a time to slopes 30 degrees and steeper, make group communication and unanimous decision making a priority, and choose your terrain wisely: eliminating unnecessary exposure and planning out your safe zones and escape routes.
The current hazard rating is MODERATE above treeline: over 2' of new snow was rapidly transported by strong north winds and formed stiff wind slabs up to 2'. Use caution if you choose to travel on wind loaded terrain - these slabs could release high and wide.
More info is available by clicking FULL FORECAST below. (All three forecast regions have the same info.)
Please share your field observations HERE.
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