0830 AM PDT SAT DEC 01 2007 && ZONE AVALANCHE FORECASTS * OLYMPICS- .AVALANCHE WATCH FOR SUNDAY AND MONDAY... Locally considerable avalanche danger above 5-6000 on north through east exposures Saturday morning, otherwise moderate below 7000 feet. Danger gradually increasing Saturday afternoon through Saturday night, becoming considerable above 4 to 5000 feet and moderate below. Avalanche danger substantially increasing Sunday and becoming high above 5000 feet and considerable below Sunday afternoon. Further increasing danger likely late Sunday through early Monday, becoming extreme above 6000 feet and high below. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST- .AVALANCHE WATCH FOR SUNDAY AND MONDAY... Locally considerable avalanche danger above 5-6000 on north through east exposures Saturday morning, otherwise moderate below 7000 feet. Danger gradually increasing Saturday afternoon through Saturday night, becoming considerable above 4000 feet and moderate below. Avalanche danger substantially increasing Sunday and becoming high above 4000 feet and considerable below Sunday afternoon. Further increasing danger likely late Sunday through early Monday, becoming extreme above 5 to 6000 feet and high below. * MT HOOD AREA- .AVALANCHE WATCH FOR SUNDAY AND MONDAY... Considerable avalanche danger on northeast through southeast facing slopes above 5000 feet Saturday morning, otherwise moderate avalanche danger below 7000 feet. Danger gradually increasing Saturday afternoon and night, becoming considerable above 4000 feet and moderate below. Avalanche danger substantially increasing Sunday, becoming high above 5000 feet and considerable below Sunday afternoon. Further increasing danger likely late Sunday through early Monday, becoming extreme above 5 to 6000 feet and high below. * WASHINGTON CASCADES EAST OF THE CREST- .AVALANCHE WATCH FOR SUNDAY AND MONDAY... Locally considerable avalanche danger above 5 to 6000 feet on north through east exposures, otherwise moderate above 5000 feet and generally low below. Danger gradually increasing Saturday afternoon and night, becoming considerable above 5000 feet and moderate below. Avalanche danger substantially increasing Sunday, becoming high above 5 to 6000 feet and considerable below Sunday afternoon. Further increasing danger likely late Sunday through early Monday, becoming high above 4 to 5000 feet and considerable below. SNOWPACK ANALYSIS While a still relatively shallow snowpack and significant vegetation, rock or other terrain anchoring are helping to limit the avalanche danger at lower elevations and along the Cascade east slopes below about 5000 feet, in most other areas where sufficient snow has accumulated to cover existing anchors, an increasingly unstable snowpack structure has developed during the past week. This structure consists of shallow amounts of relatively high density snow or crusts near the ground, about a foot or so of low density snow over the crust, buried surface hoar, and one to two feet of slightly denser and a little more cohesive wind slab in the upper snowpack, especially in the Mt Hood area and southern Washington Cascades where heaviest recent snowfall and stronger winds occurred. A trace to a few inches of very low density fluff was also deposited over this structure on Friday. Additionally, the clear and relatively cool weather about 10-15 days ago produced some serious faceting and weakening of the snow just above the old crust that lies near the ground. While the most recent field information indicates some settlement and stabilization of the multitude of buried weak layers and a lack of human triggered slides, for the most part the weak layers remain and lack only an increased load to once again become very active. Stability information received during much of the past week corroborated the generally unstable snowpack structure, with natural or human triggered avalanches ranging from those involving only the upper 8 to 10 inches to 2-3 ft slabs involving most of last months snow down to facets just above the early November crust. This snowpack structure should remain very susceptible to the destabilizing effects of loading, warming and winds, all of which are expected to become major factors from mid-late Saturday through Monday of next week. Back country travelers are urged to stay aware of what is expected to be a rapid and very significant increase in the avalanche danger this weekend. DETAILED FORECASTS SATURDAY AND SATURDAY NIGHT After mostly cloudy skies and light showers early Saturday morning, increasing light snow should reach the Olympics by mid-morning and the Cascades mid-day or early Saturday afternoon, with increasing moderate to heavy snow likely developing in most areas later Saturday afternoon and night. Along with generally increasing winds but continued low temperatures, especially near higher ridge lines, this should produce a slow but steady increase in the avalanche danger. With expected winds, the greatest danger should develop on east through north facing slopes near higher ridges, but a slow increase in east winds near the Cascade passes should also favor shallow wind slabs developing on west facing slopes there. Back country travelers should use increasing caution and test snow stability often later Saturday as loading of buried weak layers increases. SUNDAY AND SUNDAY NIGHT Moderate to heavy snowfall, increasingly strong winds and slow warming on Sunday should progressively load and stress a multitude of buried weak layers, especially on lee slopes above 4 to 5000 feet where most terrain and vegetative anchoring should be slowly buried. In such areas, a high danger is expected with natural and human triggered avalanches becoming increasingly likely Sunday afternoon. Initially, most slides may involve only the most recently received storm snow late Saturday and Sunday, with fractures extending into the lower density snow received Friday or early Saturday. However, expected instabilities should become quite sensitive and widespread, with shooting cracks, whomping, sympathetic and remotely triggered slides probable. With continued stresses added by heavy snow or rain, very strong winds and further warming late Sunday into early Monday, the probability of natural or human triggered slabs involving all of the recent snow down to the facets above the old early-mid November crust should increase dramatically. This should produce an extreme danger in terrain above about 4 to 5000 feet late Sunday. Widespread natural or human triggered avalanches should be certain on most aspects and slope angles, and despite the overall early season snowcover, some large, destructive slabs ranging up to 3 to 5 feet or more are possible. As a result, back country travel is not recommended on steeper, avalanche terrain Sunday, and back country travel should be avoided late Sunday into Monday, with any travel confined to low angle terrain well away from avalanche path runouts. &&