Problem 1: Storm Snow.
Chance: Likely. Size: Small. Location: All aspects (especially Lee aspects) above 1500'.
30" of new snow has fallen on Thompson Pass since Dec 8th with little wind. Up to 1' of new snow is expected to fall in the next 24 hrs. SE winds increased on Thursday and are forecast to up to 40mph at ridgeline . . . blowing new and old snow onto lee slopes (primarily NW). Expect small reactive slab avalanches up to 2' deep on slopes 30deg or steeper. Where the new snow is not wind affected DRY LOOSE sloughs could easily be large enough to knock over and bury a rider. Avoid loaded slopes particularly just below ridgeline (where the snowpack gets quickly 'overloaded.')
Problem 2: Persistent Slab.
Chance: Possible. Size: Large. Location: All aspects above 1500'.
There are multiple buried problem layers on ALL aspects and most elevations. There are multiple facet-crust combos buried anywhere from 1-6' 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: more snow, skiers, and snow machines. The probability of triggering a deep slab avalanche on one of these layers but the consequence could be high!
Over the past week there have been several slab avalanches on multiple aspects at different elevations up to size 2. There have been limited field observations to validate the type, trigger, or other details of these slides however; we believe they are mostly within the new snow or high in the snowpack at the new/old snow interface.
Please share field observations and photos as you get out into the field.
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` 25 F 16 F
Temp at 3000` 20-28 F 18-26 F
Chance of precip 100% 100%
(above 1000 FT) 0.51 in 0.20 in
(above 1000 FT) 7-8 in 2-3 in
Snow level sea level sea level
Wind 3000` ridges SE 15-25 mph SE 10-20 mph
Remarks...Wind gusts to 35 mph in the early morning.
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!
The avalanche danger is CONSIDERABLE above 1500' due to high volume of recent snow and complicated problem layers in the snowpack. Early season conditions: low snowpack with widespread variability. 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 and have limited snowpack data!
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