830 AM PST MON FEB 18 2008...AMD && ZONE AVALANCHE FORECASTS * WASHINGTON CASCADES, OLYMPICS, MT HOOD AREA- MODERATE avalanche danger above 5000 feet and LOW below increasing mid-late Monday morning and afternoon and becoming locally CONSIDERABLE on sun exposed terrain above 5000 feet and MODERATE elsewhere. Danger gradually decreasing Monday night and becoming MODERATE above 6000 feet and LOW below. Slightly increasing danger expected Tuesday morning, becoming MODERATE above 4000 feet and LOW below mid-day and Tuesday afternoon. Little change in the danger Tuesday night. SNOWPACK ANALYSIS In most areas at lower elevations and near the Cascade passes early Monday, a gradually thickening surface sun or melt-freeze crust has developed over 3-6 inches of recent soft and slowly settling old snow that lies over another moderate and semi-breakable crust that lies over several feet of moist to wet older snow from strong storms about 8-10 days ago. Although the breakable to walkable surface crust and relatively cool temperatures below about 5000 feet are helping to produce a generally low avalanche danger, the crust is also making for some challenging and potentially dangerous conditions if edges are not sharp. At higher elevations early Monday, warm temperatures above a mid-level inversion are helping to maintain generally moist to wet near surface snow or a relatively thin surface crust. Along with some previous wind transport, the 4 to 8 inches of relatively weak near surface snow are helping to produce a moderate danger. However, with significant amounts of recent snow still slowly settling under a second moderate crust about 4 to 8 inches below the surface, this snowpack structure remains very susceptible to the destabilizing effects of strengthening mid-late winter sun and high freezing levels, both of which are expected during the next 12 hours. As a result of anticipated warming and freezing levels around 10-12,000 feet, back country travelers are urged to use increasing caution and be aware of the state of the surface snow around them. Wet loose slides which do release from warming and melt may entrain considerable amounts of near surface snow, and these slides in turn may trigger some isolated larger wet slabs which may break through and involve older and weaker snow layers below the near surface crusts. Such a potential for larger slide releases should be greatest on slopes showing no evidence of recent avalanche activity and at higher elevations...especially steeper terrain above 7000 feet which have not experienced sustained high freezing levels since last November. DETAILED FORECASTS MONDAY With the exception of a few high clouds at times, mostly fair and increasingly warm weather is expected in most areas on Monday. While relatively light winds are likely near ridgetops, light to moderate easterly surface winds across the Cascades should maintain relatively cool conditions at lower elevations near the passes. However, the warmth and sun away from the passes and in most higher elevation terrain should allow for considerable melt of near surface snow, and this should result in increased weakening and snow creep of upper snow layers. Along with snow melting and falling from tree boughs or steep rock faces which enhance solar effects, this combination of factors should add increasing stress to upper snow layers and produce a considerable danger, with wet loose and isolated wet slabs becoming probable during late morning and afternoon hours, especially on sun exposed southeast through southwest facing slopes not experiencing recent avalanche activity. While some slides may be relatively small initially, the snow structure should allow them to entrain considerable snow as they descend, possibly triggering larger slabs as well. More isolated but larger slides are also possible at elevations above 7000 feet, especially on sun exposed but wind sheltered terrain, and travel across or beneath steeper, higher elevation, sun exposed terrain is not recommended during the heat of the day. Back country travelers should stop and take time to assess snow stability and any recent avalanche activity, and extra caution is recommended for snowmobilers as well, particularly if high marking steeper sun exposed terrain. MONDAY NIGHT Gradually lowering freezing levels, slightly increasing winds and increasing high clouds Monday night should allow for generally decreasing danger as wet surface snow refreezes and strengthens and recent snow continues to settle. TUESDAY, TUESDAY NIGHT...AMD Increasing high clouds are expected Tuesday morning with variable mid and high clouds Tuesday afternoon. Along with continued relatively high freezing levels Tuesday morning and very slow cooling Tuesday afternoon, this weather should still allow for a slight increase in the danger through the effects of considerable sun or filtered sun as well as further melt of surface snow. However, with temperatures not as warm as Monday, and some wind near higher ridges helping to limit the amount of surface snow melt (see http://www.nwac.us/education_resources/Wet_snow.pdf), the danger increase should be more limited and confined primarily to weakening and melt within upper snow layers on directly sun exposed and wind sheltered terrain. Further increasing clouds late Tuesday should be followed by further lowering freezing levels and some light rain or snow in the Mt Hood area Tuesday evening, spreading into the south-central Washington Cascades early Wednesday. However, with rather minimal snowfall amounts likely, and old refrozen or crusted snow surfaces not susceptible to erosion and transport by winds, this weather should not significantly affect the existing low to moderate avalanche danger. &&