0830 AM PDT FRIDAY NOV 30 2007 ZONE AVALANCHE FORECASTS * OLYMPICS, WASHINGTON CASCADES NEAR AND WEST OF THE CREST- .AVALANCHE WATCH FOR SUNDAY AND MONDAY... Considerable avalanche danger above 4-5000 feet and moderate below gradually decreasing through early Saturday becoming considerable above 5-6000 and moderate below. Danger gradually increasing mid-day Saturday through Saturday night, becoming considerable above 4000 feet and moderate below. * SUNDAY OUTLOOK- .AVALANCHE WATCH FOR SUNDAY AND MONDAY... Avalanche danger substantially increasing Sunday, becoming high above 4000 feet and considerable below. Further increasing danger likely late Sunday through early Monday, possibly becoming high to extreme in the Olympics and Cascades near and west of the crest above 4 to 5000 feet, and high above 5 to 6000 feet along the Cascade east slopes. 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, surface hoar layers, and now some 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. 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. A number of field reports corroborate the generally widespread instability, with significant cracking and settling being reported in a variety of areas (Mt Baker, Crystal Mountain, Chinook Pass, Mt Hood Meadows) during the past several days, along with some natural as well as human triggered avalanches. While most of the human triggered slabs have been relatively small, involving only the upper 8-10 inches of recent storm snow, some skier and explosive triggered slabs near Mt Hood Meadows involved all of the snow down to the facets above the old crust, with slab depths ranging from 2 to 3 feet. In most instances, the resulting fractures quickly propagated long distances across slope, and the associated slides ran considerable distances into the runout. 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 FRIDAY, FRIDAY NIGHT, SATURDAY MORNING As a weak upper disturbance moves mostly southward offshore on Friday, partly to mostly cloudy skies, light winds and relatively cool temperatures are likely in most areas, along with occasional light snow or snow showers, heaviest in the south. With no significant new snow accumulations likely and relatively light winds, this weather should allow recent wind slabs to begin to settle. However, a significant number of buried weak layers remain, and the relatively low temperatures should make stabilization a slow process. The greatest danger should exist on northeast through southeast facing slopes from recent westerly winds, especially in the southern Washington Cascades and Mt Hood area. Decreasing light snow or snow showers, continued light winds and cool temperatures Friday night into early Saturday should allow for a further gradual decrease in the danger as slow snowpack settlement continues. SATURDAY AFTERNOON AND NIGHT Increasing clouds and increasing light snow should reach the Olympics later Saturday 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. SUNDAY AND SUNDAY NIGHT Moderate to heavy snowfall, increasingly strong winds and slow warming on Sunday should continue to 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 on Sunday, with fractures extending into the lower density snow received Saturday. However, instabilities should become quite sensitive and widespread, with shooting cracks, whomping, sympathetic and remotely triggered slides probable. With continued loading by heavy snowfall, very strong winds and further warming late Sunday and Sunday night, expected stresses should produce natural or human triggered slabs involving all of the recent snow down to the facets above the old early-mid November crust. This may produce fractures ranging up to 3 to 5 feet or more, with a high to extreme danger likely developing in terrain above about 4 to 5000 feet. As a result, back country travel is not recommended on steeper, avalanche terrain Sunday, and back country travel should be avoided late Sunday and Monday, with travel confined to relatively low angle terrain well away from avalanche path runouts. &&