Problem #1: Storm Snow
Location: all aspects and elevations, but especially W-NW-N-NE aspects.
Heavy snowfall rates yesterday combined with moderate-strong SE winds will have created quite a bit of wind loading on lee aspects. Fresh storm slabs will be 30-60+cm thick and resting on a thick bed of weak facetted snow. Bonding to the old snow will be poor, and there will be lots of settlement. Natural and human triggered avalanches are likely in any wind loaded or cross-loaded areas. Some slides could be large and step down to old persistent slabs 60-90cm deep, causing wide propagation. Avoid all avalanche terrain. Watch out in steep clearings in the trees where new snow piles up deep and consequences are high. Stay well away from terrain traps. This new danger will likely persist for a while, due to the thick nature of the persistent facets underneath the new snow.
Problem #2: Persistent Slab
Beneath the new snow, we currently have two different persistent-slab dangers to watch out for: 1) old facet layers, and 2) buried surface hoar.
1) For the old-facets problem: Location: All aspects, at elevations above treeline where the snowpack is thin/windswept.
One concern is in areas of thin snowpack, where old facets (1-2mm) lurk underneath the wind slabs that sit 30-60cm deep. A heavy load of new snow may activate these dormant layers. Pole probing can help you map out which slopes contain hard-over-soft layering, a sign of this persistent slab danger. Remote triggering is possible, so keep track of your group and manage your exposure carefully.
2) For Buried Surface Hoar: Location: ALL elevations, clearings in the trees, and specific slopes above treeline (mainly slopes sheltered from NW winds) where surface hoar formed over the last 3-4 weeks and wasn't blown away by NW winds.
There are areas of buried surface hoar lingering at one and three layers down (roughly 50-80cm deep). These dangerous weak layers will persist for several weeks until they can be crushed and flushed out by lots of heavy snowfall. Be sure to dig around in wind sheltered areas to look for "the thin grey line" and clean shears. Assume this weak layer to be present in wind-sheltered areas. Use extra caution in openings around treeline, and avoid wind-sheltered rollovers in the alpine.
5-16" of new snow fell Saturday night - Sunday. Southeast winds were strong, and temperatures warmed up during the storm, raising snow levels to about 1500ft. Temperatures will be slowly dropping through Wednesday night, when the next storm comes in with moderate snow accumulations down to sea level.
Snow Depth [in]
Last 24-hr Snow/SWE [in]
Last 3-days Snow/SWE [in]
Today's Freezing Level [ft]
Next 24-hr Snow/SWE
12" / 1.00
1" / 0.10 *
7" / 0.60
1" / 0.10 *
5" / 0.40
( *star means meteorological estimate )
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.
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