0830 AM PST THU DEC 20 2007 AMD && ZONE AVALANCHE FORECASTS * OLYMPICS, WASHINGTON CASCADES NEAR AND WEST OF THE CREST- ...AVALANCHE WARNING FOR THURSDAY... High avalanche danger above 4000 feet and considerable danger below Thursday morning, gradually decreasing Thursday afternoon and becoming high above 5000 feet and considerable below Thursday night and early Friday. Danger continuing to slowly decrease Friday and becoming high above 6000 feet and considerable below Friday afternoon. Danger gradually increasing Friday night. * MT HOOD AREA- ...AVALANCHE WARNING FOR THURSDAY... High avalanche danger above 5000 feet and considerable below Thursday morning, slowly decreasing Thursday afternoon and becoming high above 6000 feet and considerable below Thursday night and early Friday. Further slightly decreasing danger expected on Friday, but danger gradually increasing Friday night. * EAST SLOPES WASHINGTON CASCADES- High avalanche danger above 6000 feet and considerable below Thursday morning, slowly decreasing Thursday afternoon and becoming considerable below 7000 feet Thursday night and early Friday. Further slightly decreasing danger expected on Friday, but danger gradually increasing Friday night. SNOWPACK ANALYSIS..AMENDED.. Relatively large amounts of new snow continue to be deposited over and load a variety of weaker snow layers over the old early December crust. These weak layers include lower density snowfall from last week and earlier this weak as well as some buried surface hoar. Also, some faceting and weakening of the snow near and within the old crust has continued, especially in the generally shallower snowpack along the Cascade east slopes. This has continued to further weaken or help maintain a poor bond of the recent large amounts of new snow to the old now deeply buried and decomposing crust. After receiving from 6 to about 20 inches of relatively low density snow last week, some 3 to 6 feet of generally higher density new snow has been received since last Friday. As a result, a high danger continues above 4000 feet in the Olympics and Cascades near and west of the crest, above 5000 feet in the Mt Hood area, and above 6000 feet along the Cascade east slopes with a slightly lower but still significant and considerable danger at lower elevations. Due to recent winds, the greatest danger in most areas exists on north and northeast through southeast exposures, although other aspects may be loaded near the Cascade passes. Field reports from a variety of areas, including Mt Hood Meadows, Paradise, Crystal Mountain, Alpental, Mission Ridge and Stevens Pass all indicate a dangerous snowpack structure, with many large 3-5 ft avalanche releases being reported as recently as late yesterday. Also, significant whomping reported indicates significant collapse of overlying slabs on numerous buried weak layers. While many recent avalanches have involved only the most recently deposited snow, both skier and explosive triggers have released some large slab slides stepping down to the old early December crust. As of this time, the snowshoer who triggered and was caught by a slab avalanche near Edith Basin above Paradise on Mt Rainier on Tuesday continues to be missing, with poor weather conditions and high avalanche danger hampering potential rescue efforts. As a result of all of these weather and snowpack conditions, back country travel in avalanche terrain is not recommended on Thursday. All back country travelers, whether their mode of travel is by ski, snowboard, snowmobile or snowshoe, are urged to confine travel to more gentle and tree covered terrain until the recent large amounts of new snow have had a chance to settle and stabilize. Travelers should note that although a recent decrease in winds in some areas may make the new snow surface seem soft and yielding and very attractive, this surface is masking a variety of buried weaknesses which may need only a little added stress to release. While slow snowpack stabilization should begin to occur later Thursday and Friday, more heavy loading expected to develop over the weekend should bring another substantial danger increase and maintain the potential for some very large slab slides that may still involve all of the recent snow down to the old early December crust, especially in areas not experiencing recent avalanche activity. DETAILED FORECASTS THURSDAY Light to moderate showers in the northern Washington Cascades and Olympics and moderate to heavy showers in the central and southern Cascades and Mt Hood area Thursday morning should slowly decrease Thursday afternoon. However, low temperatures and moderate ridgetop and pass winds should help maintain existing generally high avalanche danger Thursday morning with only a slight decrease in the danger likely Thursday afternoon. Hence, natural and human triggered avalanches should remain likely on a variety of aspects and slope angles Thursday above about 4 to 5000 feet and probable at lower elevations, with the danger accentuated on steeper, wind loaded terrain. THURSDAY NIGHT, FRIDAY, FRIDAY NIGHT Decreasing showers and winds are expected Thursday night and early Friday with increasing clouds and occasional light snow likely spreading to most areas later Friday morning and afternoon. However, along with generally decreased winds and cold temperatures, the lack of a further large load should allow for a slight and slow decrease in the danger as the recent large amounts of new snow continue to slowly settle and begin to strengthen. However, a relatively scary snowpack structure should persist in many areas, especially at higher elevations on lee slopes where avalanches should remain likely and travel is still not recommended. Wherever their travel takes them, travelers are urged to have shovel, probe and beacon, perform stability tests often and observe appropriate travel techniques and route selection. Increasing winds and slowly increasing light snow late Friday should be followed by stronger winds, some warming and increasing snowfall early Saturday. This should produce a gradual increase in the danger later Friday into early Saturday. &&