BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREA NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON 9 AM PST SAT JAN 31 2009 NWAC Program administered by: USDA-Forest Service with cooperative funding and support from: Washington State Department of Transportation National Weather Service National Park Service Washington State Parks and Recreation Commission Pacific Northwest Ski Area Association Friends of the Avalanche Center and other private organizations. This forecast applies to back country avalanche terrain below 7000 feet and does not apply to highways or operating ski areas. WAZ513-518-519-019-042-501-502-ORZ011-011700- && ZONE AVALANCHE FORECASTS * OLYMPICS- * WASHINGTON CASCADES FROM SNOQUALMIE PASS NORTHWARD- * CASCADE PASSES FROM SNOQUALMIE PASS NORTHWARD INCLUDING STEVENS AND SNOQUALMIE PASSES- Saturday: locally considerable danger on lee slopes above 5 to 6000 feet, otherwise moderate danger below 7000 feet Saturday night and Sunday morning: slightly decreasing danger becoming moderate above 4000 feet and low below Sunday afternoon and night: gradually increasing danger, becoming considerable above 5000 feet and moderate below * WASHINGTON CASCADES SOUTH OF SNOQUALMIE PASS- * CASCADE PASSES SOUTH OF SNOQUALMIE PASS INCLUDING WHITE PASS- Saturday morning: moderate avalanche danger below 7000 feet with greatest danger on lee terrain above 5 to 6000 feet Saturday afternoon through Sunday morning: gradually decreasing avalanche danger becoming moderate above 5000 feet and low below Sunday afternoon and night: slowly and slightly increasing danger * EAST SLOPES WASHINGTON CASCADES- Saturday: moderate avalanche danger below 7000 feet, with greatest danger on higher elevation lee slopes near the crest Saturday night and Sunday morning: slightly decreasing avalanche danger Sunday and Sunday night: slightly increasing danger, especially from about Snoqualmie Pass northward * MT HOOD AREA- Saturday morning: moderate avalanche danger above 5000 feet and low below with greatest danger on wind loaded terrain above 5 to 6000 feet Saturday afternoon through Sunday morning: gradually decreasing avalanche danger becoming moderate above 6000 feet and low below Sunday afternoon and night: slowly and slightly increasing danger SNOWPACK ANALYSIS As advertised a weak frontal system moving over the area late Friday afternoon and evening brought increasing winds and dramatic cooling but very little in the way of precipitation…with new snowfall amounts ranging from a trace to a few inches and most of this from about Snoqualmie Pass northward. In most areas the meager precipitation began as snow, but some brief rain fell below about 3 to 4000 feet before changing to snow. Also on Friday prior to the front, warming temperatures and sunshine produced a weak surface crust on sun-exposed terrain and allowed for further slow settlement and gradual strengthening of the previously sensitive wind slabs that developed early last week. Finally, in areas that experienced some clearing behind the front, mainly from about Crystal Mountain southward, some small surface hoar was reported early Saturday. In short, the near surface snowpack structure is highly variable and varies significantly from aspect to aspect and with elevation changes. However, in general the most recent weather has allowed for a gradual decrease in the dangers associated with the sensitive slabs that developed over a variety of persistent weak layers mid-week. As the overlying slabs have begun to settle and strengthen, this has decreased the stress on buried surface hoar and facets near one of several buried crusts as well as diminishing the stored energy necessary to propagate fractures. Despite this overall danger decrease and less recent snow available for transport due to a weak surface crust from either warming on Friday or rain Friday night, increased winds may have produced some new shallow and more cohesive slabs on some southeast through northeast exposure slopes, mainly above about 5000 feet in the north and 6000 feet in the south. As a result, back country travelers should continue to use caution and perform stability tests before venturing onto steeper terrain that has not experienced recent avalanche activity. DETAILED FORECASTS SATURDAY MORNING Cold temperatures, light to moderate showers in the north and central WA Cascades and scattered light showers in the south and Mt Hood area should combine with moderate though slowly decreasing winds to maintain existing danger Saturday morning as further shallow slabs are possible, mainly on northeast through southeast exposures. SATURDAY AFTERNOON THROUGH SUNDAY MORNING Decreasing light showers, heaviest in the north-central WA Cascades and some partial clearing Saturday afternoon should be followed by slow clearing overnight before clouds increase again Sunday morning with some light snow redeveloping in the Olympics and north Cascades. Along with low freezing levels and briefly diminishing winds, this weather should allow for a slow decrease in the danger through either previous avalanche activity or further slow settlement of recent wind slabs. SUNDAY AFTERNOON AND NIGHT Rising freezing levels, increasing winds and light to occasionally moderate rain or snow in the northern and central Cascades and Olympics should produce a slow increase in the danger as recent wind slabs weaken and buried weak layers receive further gradual loading through either wind transport or small amounts of new rain or snow…with greatest danger developing on wind loaded northeast through southeast exposures near higher ridges. Although only very light snowfall is expected in the south, increased winds and significant warming should nevertheless produce a slight increase in the danger there, especially on steeper lee terrain. && Backcountry travelers should be aware that elevation and geographic distinctions are approximate and that a transition zone between dangers exists. Remember there are avalanche safe areas in the mountains during all levels of avalanche danger. Contact local authorities in your area of interest for further information. 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. Also note that field snowpack information is often available on the FOAC website at www.avalanchenw.org, and weather and avalanche glossaries for commonly used terms in the forecasts can be found on the NWAC education page. Moore/Northwest Weather and Avalanche Center $$