THE BOTTOM LINE:
The avalanche danger is MODERATE at all elevations through the Thompson Pass region, HOWEVER it will rapidly jump to CONSIDERABLE overnight and on Monday December 17th due to the approaching storm with what the NWS calls an "impressive amount of moisture."
The storm on December 14 produced 12" of new snow covering most of the Valdez - Maritime region but hardly moved inland. Thompson Pass at 27mile only received 1-3". Beneath any new snow is a widely variable snowpack that has complicated layers including facet-crust combos and basel facets. EARLY season conditions combined with a lot of recent and forecasted snow - careful route finding, snowpack assessment, and team dynamics are essential to LIVE TO RIDE ANOTHER DAY!
Problem 1: Wind Slab.
Chance: Likely. Size: Small. Location: All Lee aspects. All wind exposed elevations and features.
45" of new snow has fallen on Thompson Pass since Dec 8th. Expect small Wind Slab avalanches up to 1-2' deep on slopes 35deg or steeper in Lee terrain. The predominant wind has been from the SE over the past 10 days but Saturday the wind switched from the N. That means that wind slabs have formed on MULTIPLE aspects. These new slabs are stubborn to release but could still propagate across a loaded slope . Avoid loaded slopes particularly just below ridgeline.
Problem 2: Persistent Slab.
Chance: Possible. Size: Large. Location: All elevations.
There are multiple buried problem layers on ALL aspects and most elevations. There are multiple facet-crust combos buried anywhere from 1-7' deep and also basel facets (bottom of snowpack, weak, sugar snow, up to 3mm). Stability tests have shown inconsistent results ranging from very reactive to unreactive (dormant). These layers are all showing signs of gaining strength (rounding grains) but our confidence is low of how these layers will react to large loads: skiers, snow machines, and more snow (which is forecasted for the next 48hrs). The probability of triggering a deep slab avalanche on one of these persistent weak layers is low but the consequence would be high, choose your safe zones wisely!
Problem 3: Dry Loose.
Chance: Likely. Size: Small. Location: All aspects. All Elevations.
Where the new snow is not wind affected DRY LOOSE sloughs could easily be large enough to knock over and bury a rider. Dry loose avalanches often entrain more and more snow on their way down the mountain. Be mindful of your group spacing and what terrain traps and/or cliffs are below you. Watch your SLUFF. This hazard will increase from Sunday to Tuesday.
On December 15th a small cornice was intentionally ski cut which triggered a small wind slab in steep terrain (45deg), in Loveland basin, N facing, at 4700', 12" deep.
There have been no other avalanches reported in the last several days. Please share field observations, even just from the road!
From the National Weather Service Rec Forecast:
The Thompson Pass Mountain Forecast covers the mountains (above
1000 ft) surrounding Keystone Canyon through Thompson Pass to
This forecast is for use in snow safety activities and emergency
Temp at 1000` 31 F 28 F
Temp at 3000` 22 F 20 F
Chance of precip 100% 100%
(above 1000 FT) 0.43 in 0.75 in
(above 1000 FT) 4-7 in 6-11 in
Snow level sea level sea level
Wind 3000` ridges NE 15-30 mph NE 14-28 mph
The following surface map shows the approaching storm and why the wind will be coming from the NE.
If you get out riding, please send in an observation!
Start the season with fresh batteries in your beacon, and 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.
Do you have the right route, the right group, the right skills on the right day?
Live to Ride Another Day!
Early season conditions: low snowpack with widespread variability including buried problem layers. Use caution as you enter avalanche terrain (slopes over 30deg) and be aware that avalanche terrain may be ABOVE you. Areas of thinner snowpack are more suspect for weaker and unstable snow especially further inland and north of 32 mile. We have seen a lot of recent snow, in a short amount of time, and have limited snowpack data!
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