Westerly winds on Saturday & Sunday created sensitive pockets of fresh wind drifts on a variety of aspects at the upper elevations, and increasing winds today will only elevate this hazard. Although I am not expecting these drifts to be large, they are sensitive as they are sitting on top of weak faceted snow that formed during the extended period of high pressure from Christmas thru Friday. Watch for signs of cracking and collapsing in fresh wind drifts.
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As of 6 am, mountain temperatures are in the 20's F where cooler air has pooled at lower elevation trailheads, and in low 30's F. at mid and upper elevation where warming has begun ahead of a much-needed period of storminess. Winds are out of the southwest, and have been increasing overnight, gusting in the teens at mid elevations, and 20's mph at upper elevations. At 11,000' gusts have reached 40 mph.
The general consensus is that riding conditions have greatly improved with the small, 3-5" storm from Saturday.
We received several excellent observations from Sunday, and these included reports of collapsing and cracking where westerly winds drifted stiffer slabs on top of a layer of weak faceted snow that formed during the long period of high pressure from Christmas through this past Friday. On both Saturday and Sunday there were reports of small avalanches 3-5" thick failing on this layer, however there was one larger slide on a fresh wind drift at 10,100' on east-facing Cardiff Peak that was up to 2' deep [Mark Pugliese]
The avalanche that really caught my attention, however, was on a northeast aspect at 8900' in Porter Fork in Millcreek Canyon. This was 2' deep, 150' wide, and ran 600' vertical. This avalanche ran on a weak layer that formed back in November. Control work at one Cottonwood resort also pried out a slab on a north-facing, upper elevation aspect that also failed on a mid-November weak layer. I am suspecting we will be hearing about more avalanching on these deeper layers by midweek.
Good news! A much-needed period of precipitation is on its way! Cloudy with increasing winds out of the south and west with gusts into the 30's mph. Temperatures will warm into the 40's at lower elevations, and mid 30's at mid and upper elevations. Precipitation should hold off until the evening hours, with a rain/snow line at about 8000' and several inches of dense snow overnight on a southwest flow. Currently this storm system looks to be a very equitable producer, with initially a southwest flow through Tuesday, followed by a colder northwest flow on Wednesday and into Thursday.
The snowpack at mid and upper elevations facing northwest through east are plagued with weaknesses from the ground, to the old snow surface sitting just below the Saturday storm snow. Overall the small Saturday storm wasn't enough of a load to affect deeper layers, and most activity over the weekend was in the layer of faceted snow at the old snow interface. In general you will find this layer about 3-6" down from the snow surface. However, the Cardiff Peak avalanche indicates some slides may be deeper where the slope has been wind-drifted, and the Porter Fork slide tells us avalanches failing in deeper layers buried 2'+ are possible.
With snow and wind in the forecast, this persistent slab avalanche problem will become increasingly hazardous as this week progresses.
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This information does not apply to developed ski areas or highways where avalanche control is normally done. This advisory is from the U.S.D.A. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.