Note: the danger will be rising Sunday as heavy snowfall adds stress to the snowpack, likely reaching HIGH danger by Sunday evening.
Problem #1: Persistent Slab
Location: All wind-sheltered slopes. Areas of surface hoar formed around Dec.1st, mainly on wind-sheltered slopes (including sheltered high alpine bowls). 34" of new snow has fallen over this surface hoar layer and compressed to a slab about 20" thick. The exact distribution of this dangerous weak layer is unkown, and the only way to find it will be to dig a shallow pit and shear off the new snow to carefully look for flat, shiny hoar crystals above the hard and crusty old snow. That said, one snow pit may not be representative of a whole slope. Surface hoar layers are notoriously tricky to map out. It would be best to assume this layer exists about 20" down and to assume it will be easy to trigger an avalanche on this layer. This is not a good time to be riding large or complex terrain. Wait until we have more data about this layer's distribution. Surface hoar layers do not bond over time, and must instead be crushed or flushed out by a major storm cycle. Use extra caution this weekend. Please send in any observations.
Problem #2: Wind Slab
Location: W-N-NE aspects 30-degrees and steeper, above 2000ft. New snowfall from the last week amounts to about 34" in this zone. It came in wet and heavy with strong SE winds that built up thick and dense wind slabs on lee aspects and cross-loaded gullies. Various wind slabs will have formed within this new snow, most likely to fail at depths of 3-20". Avoid wind loaded slopes and anywhere you sense slabby or hollow surface snow. Pole probing may help ID and map out these slabs (feel for hard-over-soft layering), and hand shears, slope tests, etc will be useful in evaluating reactivity.
Sporadic natural storm slab avalanches were observed from the last week, size D2-D3 on wind loaded lee aspects and gullies (above 3000ft). Crowns were around 60-90cm thick.
Saturday will be dry with increasing clouds as a new storm cylce begins Saturday night. 10-18" of new snow is likely by Sunday night, with light-moderate north winds. Light-moderate snow will continue to add up through Wednesday, with snow levels remaining at sea level.
( *star means meteorological estimate )
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.
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