The Bottom Line: The hazard rating is MODERATE in three regions due to new small Storm Slabs. Triggering older slabs is unlikely. The hazard will increase over the next few days as snow totals are expected to be over 2' by Sunday night. Good travel habits, such as exposing one person at a time, watching your partners and re-grouping in safe zones are key ways to minimize risk.
Problem 1: Storm Slab
Distribution: All aspects above treeline. Size: Small. Likelihood: Possible. Sensitivity: Reactive.
Description: Starting on March 7 new, small, storm slabs have began forming above treeline. The new snow is falling on a variety of surfaces including crusts, old slabs, and surface facets. The snowline is expected to stay below 1000' through the daytime March 9 (Saturday). These new slabs, although small, could be easy to trigger and possibly big enough to knock a rider over or into a terrain trap.
Problem 2: Persistent Slab
Distribution: All aspects above treeline. Size: Small-Large. Likelihood: Unlikely. Sensitivity: Unreactive.
Description: On January 23 a widespread layer of Surface Hoar was buried and is still a weak-PROBLEM layer. No avalanches have been reported on this layer (since Feb 15). This weak layer is unlikely to cause an avalanche; but if it did release it could propagate deeper and wider than expected. Evaluate all slopes carefully and choose safe travel protocols including one-at-a-time spacing and selecting conservative safe-zones.
Problem 3: Glide Avalanches.
There are open cracks from the port to 42-mile between 3500-4000' on multiple aspects; but predominantly on solar aspects. On Feb 28 a recently active glide crack at 3500' released wider-again, to the ground, and entrained more snow in its path (on Town Mountain). There have been multiple other 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. The best way to manage this problem is to limit (AKA avoid) travel underneath and beside them.
The current list of known open glide cracks from West to East:
Please share your field observations including signs of stable snow HERE.
The most recent NWS rec Forecast can be found HERE:
309 PM AKST Thu Mar 7 2019
The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
Temp at 1000` 23 F 34 F
Temp at 3000` 27 F 28 F
Chance of precip 70% 70%
(above 1000 FT) 0.14 in 0.14 in
(above 1000 FT) 1-2 in 1-2 in
Snow level 400 ft 700 ft
Wind 3000` ridges E 2-8 mph E 5-15 mph
SNOWPACK BIG PICTURE: Wind slabs from Feb 20-22 (which were up to 3' thick) have gained significant strength and/or have deteriorated. Below the recent wind slabs there are multiple layers that are showing good strength and structure. Of note: the Jan 23rd buried surface hoar layer is still barely reactive north of 40 mile; but is still possibly reactive in isolated pockets in steep, cold, shaded terrain throughout the entire Valdez region (buried between 30-60cm down on March 6). The further interior, the problem layers are more widespread and the snowpack is considerably shallower. New snow is falling on a variety of surfaces: old wind slab, surface facets, knocked down surface hoar, old pow, and sun crusts.
Recent snowpack history, from top to bottom:
Feb 22-March 7: Calm high pressure with overall warm temps (40F in town on multiple days) and only a few hours of moderate north winds. There have been no signs of the Jan 23rd persistent weak layer in the maritime region. There has been widespread surface facet formation; especially further north/interior and several nights with sub 0F temps.
Feb 20-22: High N-NE winds, rapidly transporting any available snow (70mph gusts). In certain places the wind built new slabs and alternatively stripped all the new snow back to old layers and rain crusts.
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 avalanche hazard rating in all 3 regions is Moderate above treeline due to building storm slabs. The hazard will quickly increase through the weekend as a series of fronts approach the southcentral coast from the southwest. All new snow will need time to bond and settle. There is the unlikely yet lingering potential to trigger older slabs (due to buried Persistent Weak Layers) . . . .
Each snowpack region has a unique forecast and hazard evaluation. Click FULL FORECAST for more information.
Please share your field observations HERE.
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