####018007045#### WWUS86 KSEW 151752 SABWA Summary Avalanche Forecast for Olympics and Washington Cascades Northwest Weather and Avalanche Center Seattle Washington 1051 AM PDT Thu Mar 15 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- ...AVALANCHE WARNING THURSDAY AND THURSDAY NIGHT... Thursday and Thursday night: Extreme avalanche danger above 5000 feet and high below Thursday. Natural and human triggered avalanches certain with some large to very large and potentially destructive avalanches. Avoid all avalanche terrain. Slightly decreasing danger late Thursday and Thursday night. Friday and Friday night: High avalanche danger above 5000 feet and considerable below Friday morning. Danger slowly decreasing Friday afternoon and night...becoming considerable on lee slopes above 5000 feet and moderate elsewhere. Saturday Outlook: Slightly increasing avalanche danger Saturday, becoming considerable on lee slopes above 5000 feet and increasing moderate elsewhere. Greatest danger shifting onto north through west exposures. Slightly decreasing danger expected Saturday night. Washington Cascades east of the crest- ...AVALANCHE WARNING THURSDAY... Thursday and Thursday night: High avalanche danger above 5000 feet and considerable below increasing Thursday morning and becoming high below 7000 feet later Thursday morning and afternoon. Human triggered avalanches very likely and some large natural avalanches are likely. Travel in avalanche terrain is not recommended Thursday. Slowly decreasing danger Thursday night. Friday and Friday night: High avalanche danger above 6000 feet and considerable below Friday morning. Danger slowly decreasing Friday afternoon and night...becoming considerable on lee slopes above 5000 feet and moderate below. Saturday Outlook: Slightly increasing avalanche danger Saturday, becoming considerable on lee slopes above 5000 feet and increasing moderate elsewhere. Greatest danger shifting onto north through west exposures. Slightly decreasing danger expected Saturday night. Snowpack Synopsis Dry and very warm weather last week caused significant snowpack consolidation and surface crust formation in most areas. This crust should limit future avalanches to layers above the crust as most more deeply buried weaknesses are sufficiently deep or bridged over by stronger layers of either wind hardened snow or several melt-freeze crusts. A return to winter began in most areas late last Friday and Saturday and persisted through Wednesday with nearly non stop storms. Storm totals of 4 to 8 feet of snow have been received in the past 5 days...all at low freezing levels with intermittenly strong winds. While already quite an unstable snowpack Wednesday when gradually denser snow was received, all of this generally weaker and colder storm snow is now being further stressed by warmer, denser snow or rain...along with further strong winds. As a result, high to extreme danger is expected Thursday...along with an increasing potential for some large and destructive avalanches. All avalanche terrain should be avoided. Thursday and Thursday night Increasingly heavy snow or rain along with brief warming and strong winds should continue to increase the avalanche danger Thursday morning when extreme danger is expected above 5000 feet in most terrain near and west of the crest and high danger at lower elevations and along the Cascade east slopes. Meanwhile a wind shift in the Cascade passes mid-late Thursday morning should produce sudden warming and a substantial increase in avalanche activity in surrounding terrain during the later morning and afternoon hours. Moderate to heavy showers at lowering freezing levels and moderate winds Thursday afternoon and night should only allow for a very slow decrease from extreme danger with general avalanche warning conditions expected to persist into early Friday...especially on wind loaded terrain. Overall, the rapid loading by warmer denser snow or rain on weak lower density snow in the upper snowpack should produce increasingly large natural avalanches for much of Thursday...as well as a greatly increased potential for human triggered avalanches which should be very likely to certain, depending on elevation. Now is the time to stay within the safer confines of ski areas where active avalanche control is performed. However, even here recreationists should be aware that all of the recent unconsolidated snow has increased the potential for suffocation in the deep snow...especially near tree wells. Don't ski or ride alone...and watch your partner! Friday and Friday night Moderate to heavy snow showers and winds should decrease Friday morning, along with continued low freezing levels. With light to moderate showers expected Friday afternoon along with relatively light winds and cool temperatures, this weather should allow for further settlement of the snowpack. Along with previous slide activity on Thursday this weather should produce a slow decrease in the danger. However, despite the danger decrease from the recent extreme, human triggered slides should remain likely on previous wind loaded terrain...especially above about 5000 feet. Any slopes receiving sun breaks between decreasing showers Friday afternoon should also see a slight increase in the danger along with some loose natural or isolated slab slides. Also...increasing and shifting winds likely late Friday should begin to increase the danger on some new lee slopes receiving wind transport. Saturday Outlook Light snow should increase and spread northward early-mid Saturday, followed by slowly decreasing light to moderate snow later Saturday. Along with moderate winds and continued low freezing levels, this should increase the avalanche danger on north through west exposures where initially shallow but increasing new wind slabs are likely. By late Saturday, shifting winds should begin to affect the danger on north through east exposure slopes where further small winds slabs should be deposited over older storm slabs. 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/