Note - No appropriate avalanche advisories could be found archived on the USFS site, their weather forecast (or the few relevant parts of it) issued the morning of Feb 19 follow below. This Avalanche Forecast comes from their accident report and clains to be for the three day spam Feb 18-20 even though they usually update the information daily. It is not clear exactly when this information was prepared or released or what exactly was available the morning of the accidents for those individuals or parties who checked. Information with predictions beyond the 19th has been deleted since the archived accidents were on the 19th. NWAC Forecast for Feb 18-20, 2012 Stevens Pass, Snoqualmie Pass, WA Cascades near and west of crest - between Stevens and Snoqualmie Pass Saturday and Saturday night: Considerable avalanche danger above 5000 feet and moderate below early Saturday increasing into Saturday night and becoming high on lee slopes above 5000 feet and considerable elsewhere...especially on north through east exposures. Sunday outlook: Slowly decreasing danger expected Sunday except for a slight increase on any slopes r eceiving sunshine. Danger continuing to slowly decrease Sunday night, becoming considerable on lee slopes above 5000 feet and moderate below. Snowpack Analysis Prior to the recent moderate to heavy snowfall arriving mid-late Friday and continuing Saturday morning, the old snow surface consisted mainly of one of the following: - generally shallow amounts of recent snow overlying strong near surface melt-freeze or sun crust layers - shallow wind deposits over an old crust on north through east exposures - a thin freezing fog or drizzle crust from Thursday night and early Friday(Alpental, Snoqualmie Pass). - thin wind slab deposits on higher elevation north through east exposures - shallow settled powder or recycled powder over a firm underlying crust - some buried surface hoar layers near Stevens Pass (recently unreactive due to burial by several thin crusts) Increasing moderate to heavy amounts of snowfall at lowering freezing levels and increasing winds were deposited over this variety of pre-existing snow surfaces mid-late Friday into Saturday morning, with up to 12-14 inches of new snowfall being reported as of mid-late Saturday morning. As temperatures cooled during precipitation, a relatively good bond of the moderate to heavy snow accumulations formed with the most of the old snow surfaces below about 5000 feet, and this temporarily helped limit the danger increase associated with the heavy snowfall. However, a gradually weakening bond with increasing elevation above 5000 feet has combined with stronger winds to create increasingly dangerous avalanche conditions on most lee slopes above 5 to 6000 feet and dangerous conditions in most avalanche terrain elsewhere. Field information from Crystal Mountain early Saturday indicates 4-8 inch soft slabs releasing easily with increasing propagation on either an old crust or previously settled old snow surface, with these slides running far and fast but as of yet only creating relatively shallow debris in the runout. Meanwhile, larger and slightly more sensitive slides have been reported from higher ridges above 5000-5500 ft on morning control at Stevens Pass where slab depths are ranging up to 8-12 inches and some slides are stepping down to facets or surface hoar above an early February crust. Also, increasing winds through the passes are just beginning to make surface snow more cohesive and able to propagate fractures over longer distances. Detailed Forecasts Saturday and Saturday night Relatively strong ridgetop and increasing pass winds, low freezing levels and moderate to heavy snow or snow showers are expected for most of Saturday, with locally heavy snow accumulations likely. This weather should combine to produce a further increase in the avalanche danger as thickening, more cohesive and somewhat brittle wind slabs develop over either the old snow surface or weaker snow layers produced between breaks between showers later Friday night or early Saturday. Some of these slabs may reach 2-3 feet or more by later Saturday and run quickly on an old smooth crust surface. As a result, increasingly dangerous avalanche conditions are expected on lee slopes near higher ridges...especially northeast through southeast exposures where human triggered avalanches should become very likely and where back country travel is not recommended. As indicated earlier, on lee slopes receiving heavy loading, some slides may involve or activate some recently buried weak layers, such as the surface hoar reported about a week ago near Stevens Pass. Also some large and unstable cornice formations are likely near higher ridges, and these overhangs as well as the slopes below should be avoided. Sunday and Sunday night Although decreasing light showers and decreasing winds are expected Sunday, cold temperatures should slow stabilization of existing wind slabs and help maintain the threat of further human triggered avalanche activity, especially on previously wind loaded terrain showing no evidence of recent avalanche activity. Also some brief sun breaks should allow for a slight danger increase on more southerly facing slopes receiving sunshine during the afternoon, when recent cornice formations should also weaken. Scattered light showers and relatively light winds late Sunday and Sunday night should allow for a slow decrease in the danger as recent wind slabs slowly settle. However, relatively cold temperatures should make such stabilization a slow process, and may begin to weaken the bond of recent snow to any of several buried crusts. Finally, in areas experiencing brief partial clearing Sunday night, some surface hoar is likely to form, and this should be closely monitored prior to the onset of light snowfall expected to redevelop on Monday. --------------------------------------------------------------------------------- Mountain Weather Forecast Northwest Weather and Avalanche Center Seattle Washington 651 AM PST Sun Feb 19 2012Note: This is archived for reference regarding avalanche incidents on Feb 19, 2012. The only archived information on the US Forest Service website consists of their weather reports, there do not appear to be any actual avalanche advisories archived. They are at least as much a weather operation as an avalanche operation. The weather information is forecast oriented so information not relevant to Sunday has been deleted. Raw data on atmospheric winds and quantitative precipiation has also been deleted. This does not leave much. Weather Synopsis for Sunday and Monday A strong front moved over the Northwest late Friday followed by an upper trough, cool northwest orographic flow and an unstable air mass on Saturday. Snowfall totals for the past couple days range from about 16 to 35 inches at sites near and west of the crest with plenty of avalanches. A broad ridge and large area of surface high pressure will linger over the northeast Pacific Ocean the next few days. A short wave ridge moving over the broader ridge and over the Northwest should cause decreasing winds aloft and decreasing snow showers on Sunday with cool temperatures. A convergence zone seen on radar Sunday early morning near Stevens Pass looks like it is dissipating. Weather Forecast for Sunday and Monday Washington Cascades near and west of the crest Stevens, Snoqualmie and White Passes Time Weather Sunday morning: Light snow showers decreasing and ending except light to moderate snow showers decreasing vicinity Stevens to Snoqualmie. Sunday afternoon: Mostly cloudy. Sunday night: Increasing clouds with increasing light rain or snow by early Monday. Winds in Miles per Hour (MPH) "Cascade Pass Level Winds" Sunday early morning: W 20-30 Sunday late morning: W 10-20 Sunday afternoon: W 5-15 Directions above indicate the direction the wind blows from on the 16-point cardinal scale. Winds near the passes tend to be highly channeled by the topography and normally blow either easterly or westerly depending on the surface pressure gradients that drive such winds.