0845 AM PST SAT DEC 15 2007 && ZONE AVALANCHE FORECASTS * OLYMPICS, WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM MT RAINIER NORTHWARD- ...AVALANCHE WATCH FOR SUNDAY AFTERNOON AND NIGHT... Considerable avalanche danger above 4 to 5000 feet and moderate below slowly increasing on Saturday and becoming high above 5 to 6000 feet, considerable from 4 to 5000 feet and moderate below 4000 feet late Saturday, except locally considerable on smooth, wind loaded terrain below 4000 feet. Greatest danger developing on northeast through southeast exposures mid-late Saturday. Avalanche danger slowly increasing early Sunday and substantially increasing mid-late Sunday, becoming high above 4 to 5000 feet and considerable below. * WASHINGTON CASCADES NEAR AND WEST OF THE CREST SOUTH OF MT RAINIER, MT HOOD AREA- ...AVALANCHE WATCH FOR SUNDAY AFTERNOON AND NIGHT... Locally considerable danger on east and northeast exposures above 5 to 6000 feet, otherwise moderate avalanche danger below 7000 feet early Saturday. Danger slightly increasing Saturday morning, but slightly decreasing Saturday afternoon and night. Avalanche danger slowly increasing early Sunday and substantially increasing mid-late Sunday, becoming high above 4 to 5000 feet and considerable below. * EAST SLOPES WASHINGTON CASCADES- Locally considerable danger on east and northeast exposures above 6000 feet, otherwise moderate avalanche danger below 7000 feet early Saturday. Danger continuing to slowly increase on Saturday, becoming considerable above 5 to 6000 feet and moderate below late Saturday, with greatest danger on higher terrain near the crest. Danger slowly increasing early Sunday and substantially increasing mid-late Sunday, becoming high above 6000 feet and considerable below. Note that in all areas, back country travel in avalanche terrain is not recommended on Sunday, and travelers should use increasing caution in avalanche terrain and with route selection on Saturday. SNOWPACK ANALYSIS In all areas, the old refrozen and increasingly hard old crust from the flooding rain event of early December is providing a strong base for the recently evolving snowpack structure. During the past week, gradually increasing amounts of initially relatively low density were deposited over the crust along with some intermittent surface hoar formation. Although new snowfall amounts during the past 12 to 16 hours have been somewhat variableranging from about 12 inches in the northern Washington Cascades near Mt Baker to 6-10 inches in the central Cascades to 3-5 inches in the southern Cascades and Mt Hood area, along with 2-4 inches along the Cascade east slopes-increased winds and some warming accompanied the snowfall. As a result, progressively more cohesive wind slabs have been deposited over these weak layers which now include sporadically buried surface hoar and some faceted and weakening snow that has developed near or just above the old crust. With these buried weak layers and a relatively poor bond of the recent snow to the crust likely in most locations, but especially on higher elevation northeast through northwest exposures, a gradually increasing and considerable avalanche danger has developed. At lower elevations, generally lighter winds are combining with a still relatively shallow snow cover and continued vegetative and terrain anchors to produce an overall lower danger. However, a moderate danger is still expected with human triggered shallow slabs possible on steeper, snow covered lee terrain having a smooth underlying ground surface. Overall, the current snowpack appears rather similar to the one preceding the heavy snow, rain and substantial avalanche activity that occurred throughout much of the Northwest in early December. With forecasts for the next few days indicating increasingly heavy snow loading of this potentially very unstable snow structure, back country travelers are urged to perform stability tests often, evaluate routes wisely, and allow for significant variations in the danger from slope to slope. Please also be aware that significant avalanche debris from the early December slide cycle may still create some challenging and potentially dangerous travel conditions near the base of many slide paths until larger snowfall amounts are received and gradually cover the frozen chunks. DETAILED FORECASTS SATURDAY, SATURDAY NIGHT Although moderate to heavy showers should gradually decrease later Saturday morning, especially in the south, increasing showers, moderate winds and continued cool temperatures from about Mt Rainier northward should create a further danger increase Saturday afternoon as gradually larger wind slabs are created, especially on southeast through northeast exposures. Although less significant shower activity is expected in the southern Washington Cascade and Mt Hood area, the combination of older weak layers, a poor bond of snow to the crust, and moderate winds should still maintain or slightly increase the existing danger. As a result, increasing caution and proper route selection are strongly advised. SUNDAY, SUNDAY NIGHT After briefly decreasing showers early Sunday, increasing light to moderate snow should spread over most areas later Sunday morning, with moderate to heavy snowfall likely Sunday afternoon and night. Along with strong winds and only a slight and brief rise in freezing levels, this weather should produce a further increase in the danger as an increasingly sensitive snowpack spreads to progressively lower elevations. Expected winds should accentuate the rapidly increasing danger on northwest through northeast exposures near higher ridges Sunday afternoon, while near the passes west facing slopes may be most heavily loaded. However, by early Monday, changing winds should shift heaviest loading onto northeast through southeast exposures. While expected slides may initially involve only the most recently deposited new snow since Saturday, as loading continues mid-late Sunday gradually larger avalanches may step down to and involve all of the new snow over the early December crust, with slab depths ranging up to 2 to 4 feet or more. With both natural and human triggered slides becoming increasingly likely by later Sunday, back country travel in avalanche terrain is not recommended on Sunday. Safest travel should be on windswept or wind scoured ridges or lower angle terrain not connected to steeper slopes above. However, please note that due to the expected strong winds, very dramatic variations in snow structure and stability are likely over short distances. Some wind exposed terrain may be scoured down to the old crust and have an associated low avalanche danger while immediately adjacent lee slopes may be heavily loaded and very unstable. &&