Backcountry Avalanche Forecast for Aspen (Forecast for Vail/Summit follows below, which includes the south side of Loveland Pass) Issued 02/14/2010 7:10 AM by Brian McCall Highlights Storm totals over the last two days have ranged from 6-12+ inches of new snow depending on location around the Aspen zone. Near and above treeline moderate to strong NW winds have transported that new snow, forming tender slabs and increasing the avalanche danger in the backcountry. At least 3 new avalanches were observed on wind loaded slopes Saturday including one larger remotely triggered avalanche on the Highlands Ridge. Caution is needed if you are traveling around wind loaded slopes near and above treeline today. Expect to see tender conditions, isolated natural avalanches, and easily triggered ones in lee and cross loaded terrain. Avalanche Danger The avalanche danger for the Aspen zone is CONSIDERABLE on N-NE-E-SE-S-SW aspects near and above treeline. New snow and stronger winds have formed tender slabs on these aspects. Deeper weak layers are also a concern on these higher elevation slopes and those new wind slabs could step down and fail in lower snowpack facets and depth hoar. On other aspects near and above treeline and all slopes below treeline, the danger is MODERATE. Snow & Avalanche Discussion Weather stations are showing another 3-5” of new snow in the last 24 hours around the zone. This will bring storm totals to 6-10” in most areas for the last couple days. A few locations around the valley that are favored by our current Northwest wind flow did pick up higher storm totals. Our forecasters on Independence Pass Saturday noted around 12+” of low density new snow in that area with a few more inches falling overnight. Moderate to strong Northwest winds that blew during the day Saturday have transported that new snow, forming tender slabs near and above treeline. For today wind will shift a bit to the North and may continue to load slopes near and above treeline. A few avalanches were observed on Saturday as a result of this storm. Observers on the Highlands Ridge noted a large remotely triggered avalanche in the K Chutes area. It occurred on a NE aspect above treeline, starting initially as a small pocket of wind slab, and stepping down to lower snowpack weak layers and running 1500 vertical feet. In the Green Mountain area of Independence Pass, observers noted one smaller natural avalanche on a Southeast aspect at 11,600 ft, and one small remotely triggered avalanche on a North aspect at 11,800 ft. Both of the occurred in wind loaded pockets, failing just below the new snow and wind slabs. Below treeline and out of the wind effects, a couple observations submitted this morning noted some sluffing of this new snow layer as well. If your backcountry tours take you into higher elevations today, expect to find some tender conditions. Watch for those new slabs on lee and cross loaded terrain features on many aspects near and above treeline. They will be easily triggered by backcountry travelers. New slabs up to two feet thick were observed yesterday, and with more new snow and wind during the evening hours, these slabs have continued to grow. Those winds slabs may be your first indication of instability in the snowpack today but older persistent weak layers are also a concern for larger avalanches. Weak layers can be found in all portions of the old snowpack at this time. Our generally shallow and below average snowpack this season comes with a high degree of variability and numerous combinations of slabs and weak layers. Frequent snowpack observations will help sort out some of the different weak layers on different aspects and elevations. As you drop below treeline today and out of the effects of the stronger winds, you will find lower avalanche danger. This storm’s low density new snow will have less effects on the old snowpack weak layers, especially in areas with lower storm snow totals. Human triggered avalanches are still possible below treeline though. These will include some sluffing and soft slabs in the new snow layer and potential for triggering some older snowpack weak layers in isolated areas as well. Weather Discussion Colorado is being squeezed between a ridge of high pressure in the southwest and a deep low-pressure system over the Great Lakes. Today weather over the southwestern portion of the state will reflect the ridge, while northwest flow moving into the low-pressure system will dominate the Northern Mountains. The flow over the Northern Mountains will dry out during the day, but there is enough low-level moisture and instability to produce convection and snow showers through the early afternoon. Northwest winds will be less than 20 mph in the valleys, but stronger along the high ridgelines. Strong winds will extend into the eastern part of the Central Mountains. The southwestern portion of the state will have partly cloudy to mostly clear skies and moderate northwesterly winds. The flow over Colorado remains northwesterly on Monday and another, but weaker, burst of energy moves through. Backcountry Avalanche Forecast for Vail & Summit County (Forecast for Aspen zone is above) Issued 02/14/2010 8:07 AM by Ethan Greene Moist northwest flow brough periods of heavy snowfall to the Vail and Summity County zone on Saturday. The terrain had a huge affect on the snowfall, so snow totals will be higher as you move up in elevation. 24 hour totals are 4" at Arapahoe Basin, 7" at Copper Mountain and Breckenridge, 5" at Ski Cooper and on Freemont Pass, 9" at Vail Mountain, and 4" at Beaver Creek.Overnight the winds blew in the 15 to 25 mph range from the northwest with gusts in the 40's and 50's. Today expect some sensitive soft slab avalanches in wind-loaded areas that are near and above treeline. Both natural and human triggered avalanches are likely in these areas. Avalanche Danger The avalanche danger for the Vail and Summity County zone is CONSIDERABLE on N-E-SW aspects. Pockets of HIGH danger exist on steep wind-loaded slopes that face NE-E-SW and are near and above treeline. Elsewhere, the danger is MODERATE. Snow & Avalanche Discussion On Saturday reports from the backcountry describe some great riding conditions. The snow came it hard in the morning and intensified in the afternoon. As a result we didn't hear much about the avalanche conditions, but there were a few natural soft slab avalanches reported from the northern Sawatch and Ten Mile ranges. Observers described them as reactive with very clean breaks. The largest avalanche reported was triggered with explosives and was over 2' deep, 450' wide and ran 1000' down a southeast facing slope. There was also a human triggered avalanche in the East Vail area. It released on a northeast facing slope at about 10,800'. It broke 1.5' deep, 75' wide and rad 200' vertically. It was triggered by a skier, but fortunately no one was injured. Today the snowfall will ease off, but the ridgetop winds will continue throughout the day. Most avalanches will break at the base of the new snow layer that formed over the last few days. This layer is generally 8-12" deep but could be twice as thick in wind-loaded or high-elevation areas. The other issue is that the snow near the ground remains faceted and weak. If you get a decent sized wind pillow to move, it could break into deeper layers and produce a very dangerous avalanche. Watch for changing conditions throughout the day as wind speeds ebb and flood. Watch for cracking and collapsing in the new and recent avalanches especially in near and above treeline areas. Avoid traveling on or underneeth steep wind-loaded slopes and give cornices a wide berth. Weather Discussion Colorado is being squeezed between a ridge of high pressure in the southwest and a deep low-pressure system over the Great Lakes. Today weather over the southwestern portion of the state will reflect the ridge, while northwest flow moving into the low-pressure system will dominate the Northern Mountains. The flow over the Northern Mountains will dry out during the day, but there is enough low-level moisture and instability to produce convection and snow showers through the early afternoon. Northwest winds will be less than 20 mph in the valleys, but stronger along the high ridgelines. Strong winds will extend into the eastern part of the Central Mountains. The southwestern portion of the state will have partly cloudy to mostly clear skies and moderate northwesterly winds. The flow over Colorado remains northwesterly on Monday as another, but weaker, burst of energy moves through.