The Bottom Line: The hazard rating is HIGH in all 3 regions with both wet avalanches and storm slabs likely. Avoid all Avalanche terrain.
Problem 1: Wet Avalanches
Distribution: All aspects below 3000'. Size: Small to VERY Large. Likelihood: Almost Certain. Sensitivity: Touchy.
The freezing level is rising above 3000' on Sunday and potentially 4000' on Monday. 2" more of rain/SWE is expected through Monday. This recipe is easy to forecast: heavy rain on snow means wet avalanches - both SLAB and LOOSE and they could be LARGE (D3+ is possible). Avoid all avalanche terrain below the freezing level and avoid traveling BELOW avalanche paths.
Problem 2: Storm Slab
Distribution: All aspects above Treeline. Size: Small-Large. Likelihood: Likely. Sensitivity: Touchy.
Description: Starting on March 7 storm slabs up to 2' have been forming above treeline. The new snow is sitting on a variety of surfaces including crusts, old slabs, surface hoar, and facets. There has only been small periods of significant south and east winds which has allowed for mostly uniform loading. As recently as March 12, skiers have been able to trigger slabs up to 1.5' both within the new snow and at the old-new snow interface. NOTE: Further interior, slabs will have a greater potential to propagate wide due to persistent weak layer bed surfaces and overall shallower snowpacks.
Special Note: Glide Avalanches.
There are open cracks from the port to 42-mile between 3500-4000' on multiple aspects; but predominantly on solar aspects. There has been much more glide activity through the main part of the winter than normal. There have been multiple other full releases near Girls Mtn, Deserted Glacier, and Town Mtn. 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:
342 PM AKDT Sat Mar 16 2019
Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
Temp at 1000` 38 F 45 F
Temp at 3000` 31 F 32 F
Chance of precip 100% 100%
(above 1000 FT) 0.63 in 0.79 in
(above 1000 FT) 0 in 0 in
Snow level 2500 ft 2600 ft
Wind 3000` ridges SE 8-19 mph E 7-16 mph
Remarks...Snowfall amounts above the snow level will be in the
6-12 inch range both tonight and again on Sunday. Heavier snowfall
amounts expected Sunday night.
SNOWPACK BIG PICTURE: Above 3000' there is 2-3' of new snow sitting on a variety of old surfaces from the high and dry previous 2 weeks. Mostly the new snow is bonding well to the old surface; but the further interior (north of 35 mile) now has buried facets and surface hoar. The January 23rd buried surface hoar has been dormant for several weeks. Except for rare, interior, isolated slopes, our avalanche problems are within the new snow or at the new/old interface. Below 2000' the snow is moving towards isothermal.
Recent snowpack history, from top to bottom:
March 7-Present: A consistent series of gulf lows have been producing slow and steady precipitation. 2.4" SWE in Valdez, and 3.1" at Thompson Pass which produced up to 3' of new snow above 3000'. There has been light-moderate south and easterly winds loading north and west faces slightly more than east and south faces. There have been no reports of natural slab avalanches in March, but numerous small wet loose avalanches in steep, low elevation terrain.
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.
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 23rd layer).
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' which buried the Jan 23rd Surface Hoar layer.
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: 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.
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.
LARGE natural WET AVALANCHES are expected below 4000' through Tuesday. At higher elevations, expect natural and human triggered STORM SLAB avalanches on all aspects. Avoid all avalanche terrain until the new moisture has time to set up. The hazard rating is HIGH at all elevations and aspects in all 3 zones.
Click FULL FORECAST for more information.
Please share your field observations HERE.
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