0900 AM PST THU JAN 10 2008...AMD && ZONE AVALANCHE FORECASTS...AMENDED * OLYMPICS, WASHINGTON CASCADES, MT HOOD AREA- ...AVALANCHE WARNING FOR THURSDAY AND THURSDAY NIGHT... High avalanche danger below 7000 feet Thursday and Thursday night. Danger gradually decreasing Friday, becoming considerable above 4000 feet and moderate below late Friday. Danger gradually increasing again Friday night into early Saturday. SNOWPACK ANALYSIS In all areas, increasingly large wind slabs and several recent weak layers that developed during periods of cool showery weather and diminished winds earlier this week have been loaded by increasing amounts of higher density snowfall overnight and early Thursday. This has created a generally high avalanche danger below 7000 feet in all areas with an increasingly unstable snow structure developing in the upper part of the deepening Northwest snowpack. Field reports from highway and some ski area avalanche control early Thursday indicates a relatively sensitive snowpack with explosive triggered slabs mostly in the 8 to 16 inch range, but quickly traveling long distances and experiencing good fracture propagation. As a result, back country travel in avalanche terrain is not recommended and travelers should confine travel to lower angled terrain not connected to steeper terrain above. While initially most avalanches should involve only the most recently deposited 1 to 2 feet of wind transported snow received overnight and early Thursday, surface slides that release may trigger some deeper slides reaching the buried weak layers formed early this week, with potential fracture depths reaching up to 3 to 6 feet or more. Additionally, with the amount of new loading expected on Thursday, some isolated larger climax slides reaching even more deeply buried weak layers are possible, especially along the Cascade east slopes where a generally weaker snow structure exists all the way to ground. Potential triggers for larger slide releases to more deeply buried weak layers should apply particularly, but not exclusively to, larger loads, such as cornice falls, snowmobilers, and larger groups. DETAILED FORECASTS THURSDAY, THURSDAY NIGHT Moderate to heavy rain or snow should decrease and become more showery early-mid morning in the Olympics and later Thursday morning in the Cascades along with further slight warming. This should maintain current high danger as higher density and wind driven snow spreads to most areas with rain or mixed rain and snow likely below about 3500 ft in the north and 4500 ft in the south. Such weather should further load and stress a variety of buried weak layers, especially near the Cascade passes when a wind shift to warmer westerly occurs later Thursday morning. With several upper disturbances and a moderate westerly flow likely maintaining moderate to heavy snow at very slowly lowering freezing levels Thursday afternoon through early Friday, the generally high avalanche danger should continue, with the danger likely accentuated on north, northeast and east exposures receiving additional wind transported snow accumulations. With gradually larger human and naturally triggered slides becoming increasingly likely on Thursday, especially on wind loaded slopes, back country travel in avalanche terrain is not recommended. FRIDAY, FRIDAY NIGHT...AMENDED Moderate to heavy showers and winds should slowly decrease mid-late Friday morning, with relatively light winds, light showers and some partial clearing likely in most areas Friday afternoon. With moderate temperatures, this should allow for the danger to slowly decrease. In the absence of further heavy loading, significant snowpack settlement is expected and recent wind slabs should slowly stabilize, especially at lower and mid elevations where rain affected or wet snow should begin to refreeze and strengthen. However, colder temperatures at higher elevations should make settlement a slower process, especially on lee slopes where some larger human triggered wind slabs should remain probable. Increasing winds, slow warming and increasing light snow expected to develop Friday night should lead to generally increasing avalanche danger by early Saturday. &&