0900 AM PST Thursday, December 24, 1998 ZONE AVALANCHE FORECASTS..... WASHINGTON CASCADES. . . .OLYMPICS. . . . Increasing avalanche danger Thursday becoming high above 5000 feet and considerable below by afternoon. Avalanche danger remaining high above 5000 feet and considerable below through early Christmas Day. gradually decreasing. Further increasing danger later Christmas remaining high above 4 to 5000 feet and considerable below through Friday night. MT HOOD AREA. SOUTHERN WASHINGTON CASCADES. . . . Increasing avalanche danger Thursday becoming high above 6000 feet and considerable below by afternoon. Avalanche danger remaining high above 6000 feet and considerable below through early Christmas Day. gradually decreasing. Further increasing danger later Christmas remaining high above 5-6000 feet and considerable below through Friday night. SNOWPACK ANALYSIS......... Increasing snow early Thursday and increasing ridgetop winds have deposited some 4 to 6 inches of new snow over most areas by Thursday morning. This new snow has fallen on either weak recrystallized snow, small surface hoar, intact stellar crystals or a smooth and hard crust. In an case, the new snow is now loading the underlying weak snow or is weakly bonded to the crust, causing widespread but relatively small natural avalanches, mainly above about 5000 feet where stronger winds are present. While these slab avalanches may be relatively shallow and break up quickly, backcountry travelers should avoid steep open slopes, especially above terrain traps such as cliffs, rocks or trees. In most areas the smooth hard near surface crust, now buried some 4 to 10 inches below the surface, should provide a slick sliding surface for avalanches to release on. On steeper slopes, it may be extremely difficult to arrest a fall or stop if caught in a small slide. It should be noted that the recent cold temperatures and the very strong temperature gradient in the upper snowpack has continued to cause recrystallization or faceting of the snow layers near or just above the crust. This process has also been gradually weakening the crust itself, mainly at higher elevations where the crust was thinner. Recent snowpit data over the past two days has confirmed this, indicating that weak lower density snow exists to near a foot below the crust. This structure should cause a significantly increasing danger when loaded with wind deposited snow or higher density snowfall expected over the next few days. Avalanches which begin sliding on the crust may break below the crust and entrain significant weak snow below, resulting in more substantially dangerous avalanches. Backcountry travelers should use extreme caution, especially in areas receiving more significant new snow and wind transported snow. The greatest danger is expected to develop on mainly northeast through east facing slopes along the west slopes. THURSDAY. Moderate to occasionally heavy snow Thursday morning and afternoon with increasing ridgetop winds. This should cause a significantly increasing danger, especially at higher elevations on lee slopes where natural or triggered slab releases are expected. Unstable windslab conditions are expected to develop on mainly northeast through east facing slopes, especially above about 5000 feet. Due to the smooth hard underlying crust and weak near surface snow or hoar frost, sensitive human triggered slab avalanches are expected to develop by later Thursday on these steep lee slopes and backcountry travelers should use extra caution. CHRISTMAS DAY. Occasional light snow early is expected to increase by the afternoon to become light to moderate during the afternoon and night with rising freezing levels and moderate winds. This should deposit further dense snow on a weak snowpack, resulting in further natural or triggered slab releases, especially on slopes, which had not recently released. Backcountry travelers are urged to use extreme caution and avoid steep slopes and slopes above terrain traps.