BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON CASCADES AND MT HOOD AREA NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON 835 AM PST THU FEB 05 2009 COR 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-ORZ011-061700- && ZONE AVALANCHE FORECASTS * OLYMPICS- * WASHINGTON CASCADES NEAR AND WEST OF THE CREST FROM SNOQUALMIE PASS NORTHWARD- * CASCADE PASSES FROM SNOQUALMIE PASS NORTHWARD, INCLUDING STEVENS AND SNOQUALMIE PASSES- Thursday: locally moderate danger on north through east exposures above 5 to 6000 feet, otherwise low avalanche danger slightly increasing Thursday night: further slightly increasing avalanche danger becoming moderate above 5000 feet and low below Friday morning: little change in the danger Friday afternoon and night: gradually decreasing danger becoming moderate above 6000 feet and low below * WASHINGTON CASCADES NEAR AND WEST OF THE CREST SOUTH OF SNOQUALMIE PASS- * CASCADE PASSES SOUTH OF SNOQUALMIE PASS, INCLUDING WHITE PASS- Thursday morning: low danger below 7000 feet Thursday afternoon and night: slowly increasing avalanche danger becoming moderate above 4 to 5000 feet and low below Friday morning: further slightly increasing danger Friday afternoon and night: gradually decreasing danger becoming moderate above 5000 feet and low below * EAST SLOPES WASHINGTON CASCADES- Thursday morning: low danger below 7000 feet Thursday afternoon and night: slowly increasing avalanche danger becoming moderate above 5 to 6000 feet and low below Friday morning: further slightly increasing danger, mainly higher terrain near the crest Friday afternoon and night: gradually decreasing danger becoming moderate above 6000 feet and low below * MT HOOD AREA- Thursday morning: low danger below 7000 feet slightly increasing Thursday afternoon and night: further slowly increasing avalanche danger becoming locally considerable on lee slopes above about 6000 feet and moderate elsewhere Friday morning: little change in the danger Friday afternoon and night: gradually increasing danger becoming moderate below 7000 feet SNOWPACK ANALYSIS DETAILED FORECASTS Although highly variable surface snow conditions continue early Thursday in most areas, the overall avalanche danger remains relatively low except for possible shallow wind slabs on sun shaded terrain in the northern WA Cascades and a recent slightly increasing danger during the later morning and afternoon hours on sun exposed terrain. These mostly stable surface snow conditions range from a varying strength melt freeze crust on most sun exposed terrain to breakable and somewhat faceting crusts on sun shaded terrain along with some patchy and shallow recent loose and faceting snow accumulations interspersed with the crusts. Also, in some steeper higher elevation sun shaded terrain that experienced significant avalanching with the early January rain event, field reports indicate that much of the 1 to 3 feet of snow that has been deposited since then remains fairly fragile and faceted. Finally, some mainly small but highly variable surface hoar deposits have been forming overnight. While much of this hoar frost is being destroyed on a regular basis by either warming or sunshine, some deposits are persisting on steeper sun shaded terrain. Although some cracking and whumpfing was reported late last week and last weekend in some areas, presumably due to buried surface hoar or facets lying under shallow wind slabs or weak crusts, the very small amounts of recent loading have produced little stored energy and little stress on the variety of buried weaknesses, with a resulting low propagation potential for any local fractures that do initiate near cracks or whumpfs. Despite the rather good corn snow conditions that have developed on some steeper sun exposed southeast through southwest facing terrain over the past few days, challenging and somewhat hazardous travel conditions have also been reported on shaded northeast through northwest exposure terrain where a variety of varying strength breakable and faceted crusts or snow layers persist near the surface. Also in some steeper terrain, the development of increasingly strong crusts and some areas of blue ice should raise further flags of caution, as a slip or fall on such surfaces may result in a long and potentially dangerous slide for life on the smooth hard surface. THURSDAY AND THURSDAY NIGHT Increasing mid and high clouds Thursday morning should be followed by gradually lowering clouds mid-day and Thursday afternoon with some light rain or snow spreading northward Thursday afternoon and night along with significant cooling. This should produce a slow increase in the danger as mostly small amounts of new snow are deposited at gradually lower elevations, with moderate danger likely developing above about 4 to 5000 feet in most areas overnight. In the Mt Hood area where slightly heavier precipitation and strongest ridgetop winds are expected, locally considerable danger is possible on wind loaded southeast through northeast exposures above about 6000 feet, as a weak bond of new snow to either an old crusted snow surface, areas of surface hoar or some near surface faceting. At lower elevations in all areas, smaller amounts of new snow and a better bond of the snow to the old snow surface should produce a slower and more limited increase in the danger. It should be noted that with the significantly lowering freezing levels, a rather poor bond is expected between the new snow and the wide variety of old snow surfaces above about 4000 feet in the north and 5 to 6000 feet in the south. In these higher elevation areas that receive any wind transport, this should result in gradual development of shallow but somewhat sensitive wind slabs. FRIDAY AND FRIDAY NIGHT…CORRECTED Light to occasionally moderate snow should become mainly light snow showers Friday morning. Along with further cooling and mostly light ridgetop winds in the Olympics and most of the northern and central Washington Cascades Friday morning, this weather should maintain existing moderate danger in these areas above about 4 to 5000 feet, where some shallow wind slabs are possible on lee slopes. However, in the southern Washington Cascades and Mt Hood area where stronger winds and slightly heavier showers are likely, a further slight increase in the danger is expected, especially on northeast through southeast facing slopes above 5 to 6000 feet where some sensitive 6 to 12 inch wind slabs are probable. Low freezing levels, decreasing light showers and winds Friday afternoon and some slow clearing Friday night should allow for gradually decreasing danger as new, generally shallow wind slabs begin to settle. && 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 $$