####018006714#### WWUS86 KSEW 231922 SABWA Summary Avalanche Forecast for Olympics and Washington Cascades Northwest Weather and Avalanche Center Seattle Washington 1122 AM PST Thu Feb 23 2012 This forecast applies to back country avalanche terrain below 7000 feet and does not apply to developed ski areas or highways. Avalanche Forecast Olympics- Washington Cascades near and west of the crest north of Stevens Pass- Thursday and Thursday night: Considerable avalanche danger on lee slopes above 5000 feet and moderate below early Thursday. Danger slowly decreasing lee terrain but slightly increasing southerly facing slopes receiving sunshine. Danger slightly increasing Thursday night. Friday and Friday night: Considerable danger on lee slopes above 6000 feet and moderate below increasing Friday and becoming high on lee slopes above 5000 feet and increasing considerable elsewhere. Saturday outlook: Danger further increasing and becoming high above 5000 feet and on lee slopes above 4000 feet and increasing considerable elsewhere. Washington Cascades near and west of the crest from Stevens Pass southward- Thursday and Thursday night: Considerable avalanche danger on lee slopes above 5000 feet and moderate below early Thursday. Danger slowly decreasing lee terrain but slightly increasing southerly facing slopes receiving sunshine. Danger slightly decreasing Thursday night. Friday and Friday night: Considerable danger on lee slopes above 6000 feet and moderate below slightly increasing Friday morning and substantially increasing Friday afternoon and night and becoming high on lee slopes above 6000 feet and increasing considerable elsewhere. Saturday outlook: Danger further increasing and becoming high above 5000 feet and on lee slopes above 4000 feet and increasing considerable elsewhere. Cascade east slopes- Thursday and Thursday night: Considerable avalanche danger on lee slopes above 6000 feet and moderate below early Thursday. Danger slowly decreasing lee terrain but slightly increasing southerly facing slopes receiving sunshine. Danger slightly decreasing Thursday night. Friday and Friday night: Moderate avalanche danger below 7000 feet increasing Friday and becoming considerable on lee slopes above 5000 feet and increasing moderate elsewhere. Saturday outlook: Danger further increasing and becoming high on lee slopes above 5000 and considerable elsewhere. Snowpack Synopsis In most areas moderate amounts of decreasing density snowfall were received on Wednesday following heavy amounts of either wet heavy snow or rain on Tuesday. Along with very slowly decreasing winds and lowering freezing levels, this allowed the old wet or moist snow layers to slowly refreeze and strengthen while depositing small to moderate amounts of new and colder snow over the old refreezing snowpack. Due to this refreezing and strengthening, widespread avalanching on Tuesday and Wednesday and significant settlement of the large amounts of snow received last Friday and Saturday, an overall gradual decrease in the danger has occurred late Wednesday thru early Thursday. However, recent moderate ridgetop and pass winds have still enhanced the danger from the recent colder snowfall on lee slopes where locally considerable danger remains above about 5000 feet from some new shallow wind slabs lying over firmer and strengthening snow layers. Thursday and Thursday night Light snow showers should decrease Thursday along with gradually decreasing winds and continued cool temperatures. Although this should allow for continued refreezing of the wetter and denser upper part of the snowpack along with further slow settlement of both the old snowpack and newer shallow slabs on lee slopes, a slight increase in the danger is likely on sun exposed terrain later Thursday morning and early afternoon where the threat of small loose or isolated shallow slabs should increase. Increasing high clouds by later Thursday afternoon should be followed by some light snowfall in the Olympics and northern WA Cascades overnight along with increasing winds in the north. Further south generally lighter winds and only some light snow showers are expected. This weather should allow for a slight increase in the danger in the north and Olympics overnight, but slightly decreasing danger in the southern and central Cascades. Despite the overall slowly decreasing danger Thursday, careful snowpack evaluation, cautious routefinding and conservative decision-making is encouraged in higher elevation terrain where large amounts of recent heavy snow are still stabilizing. Friday and Friday night After increasing light rain or snow and increasing winds in the north and Olympics Friday morning, increasing moderate rain or snow, lowering freezing levels and strong winds should spread over the region Friday afternoon, with moderate to heavy showers, strong winds and further cooling likely Friday night. This weather should result in generally increasing considerable to high avalanche danger Friday afternoon and night, with the greatest danger depending on elevation and exposure. Saturday Outlook Moderate to heavy snow or snow showers are expected for most of Saturday with heavy accumulations likely, especially along the west slopes of the Olympics and areas areas near and west of the Cascade crest with generally lighter amounts along the Cascade east slopes. Along with low and lowering freezing levels and moderate to strong ridgetop and pass winds, this weather should create larger and more unstable wind slabs.. with high danger slowly descending to lower elevations especially on lee terrain. Due to the increasingly dangerous avalanche conditions likely Saturday, back country travel in avalanche terrain is not recommended, especially on mid and higher elevation terrain showing evidence of wind transport. 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. Moore/Northwest Weather and Avalanche Center Seattle Washington References 1. http://www.nwac.us/