####018004630#### WWUS86 KSEW 212033 SABWA Summary Avalanche Forecast for Olympics and Washington Cascades Northwest Weather and Avalanche Center Seattle Washington 1233 PM PST Tue Feb 21 2012 This forecast applies to back country avalanche terrain below 7000 feet and does not apply to developed ski areas or highways. Avalanche Forecast Olympics, Washington Cascades near and west of the crest AVALANCHE WARNING FOR EXTREME DANGER TUESDAY Tuesday: Avalanche danger becoming extreme above 4000 feet and high below Tuesday and continuing Tuesday night. Wednesday: High avalanche danger above 5000 feet on lee slopes and generally considerable below and gradually increasing, especially Wednesday morning. Slowly decreasing danger late Wednesday and Wednesday night. Washington Cascades east of the crest AVALANCHE WARNING TUESDAY Tuesday: High avalanche danger below 7000 feet Tuesday and continuing Tuesday night. Wednesday: Considerable avalanche danger above 5000 feet and moderate below and gradually increasing, especially Wednesday morning. Slowly decreasing danger late Wednesday and Wednesday night. Snowpack Synopsis Fair and mild weather in early February produce a widespread and strong melt-freeze crust in most areas to high elevations. Periodic but weak weather systems in mid February each deposited snow totals of about 6 to 12 inches. Some surface hoar formed during this time during fair weather between weak disturbances. Snowpits yesterday near WA Pass indicated the buried hoar frost was 2-3 cm and buried about 1 to 2 feet. Near Stevens Pass the layer may now be buried some 2 to 4 feet. This layer should become increasingly active with the expected additional loading and warming Tuesday. More recently, a very strong storm system began late last Friday depositing some 2-3 feet of snow by early Sunday at most west slope locations but with much less new snow received along the east slopes. However the recent snow was accompanied by strong crest level winds that built widespread unstable slab conditions over weaker snow or buried hoar frost all over the smooth crust sliding surface in many areas. These unstable snowpack conditions contributing to multiple avalanche accidents at west slope locales including two fatal accidents Sunday that claimed four lives. Tuesday Very strong west flow is carrying abundant warm frontal precipitation into the region at rising freezing levels. Heavy snow changing to rain is occurring early Tuesday. The warmest air is expected over the region Tuesday afternoon and evening with rain to high elevations and heavy amounts of precipitation loading. This weather will produce widespread certain avalanches, with large to very large avalanches in many areas. Some slides could reach 3 to 6 feet or more in areas where significant wind loading occurred. In addition large recent cornices may become weak and fail, possibly triggering large slides on slopes below. As a result of these conditions, it is recommended that all avalanche terrain be avoided Tuesday. Wednesday A strong cold frontal passage is expected early Wednesday. This front will be accompanied by continued heavy precipitation at lowering freezing levels, especially Wednesday morning through midday. As freezing levels lower, new wind slab formations should build on lee slopes over the refreezing wet snowpack. At lower elevations, abundant wet snow should slowly begin to stabilize with additional new snow loading by later Wednesday. The greatest danger Wednesday should be from new unstable wind slabs on lee slopes at higher elevations, mainly northeast to southeast facing, especially below ridges on steep open slopes. While the overall danger should be significantly less than Tuesday, very dangerous avalanche conditions are expected at higher elevations on lee slopes where travel in avalanche terrain is not recommended n/a n/a NWAC weather data and forecasts are also available by calling 206-526-6677 for Washington, 503-808-2400 for the Mt Hood area, or by visiting our Web site at www.nwac.us. Kramer/Northwest Weather and Avalanche Center Seattle Washington References 1. http://www.nwac.us/