Detailed Avalanche Forecast Northwest Weather and Avalanche Center Seattle Washington 1128 AM PDT Sat Mar 26 2011 Note: This is archived in conjunction with an avalanche fatality Mar 27, the next day. Since these are issued mid-morning the group would not have seen the one dated 3/27. Mid-morning is an odd time to publish an advisory, most centers issue them either very early or the previous evening. Please remember that these forecasts are for BC avalanche terrain below 7000 ft...and do not apply to developed ski areas or highways. WAZ513-518-519-019-042-520-521-ORZ011 Zone Avalanche Forecasts - Stevens Pass Forecast Saturday and Saturday night: Moderate danger above 5000 feet and low below, slightly increasing on local lee slopes mainly above 5000 feet. Slightly decreasing danger Saturday night. Sunday and Sunday night: Moderate danger above 5000 feet and low below, slightly increasing on local lee slopes higher elevations. Decreasing danger Sunday night. Snowpack Analysis Over the past week a series of generally weak fronts have lifted across the region each depositing relatively small amounts of new snow each day, mainly from 2 to 6 inches. The most recent band Friday continued this pattern depositing about 2 to 4 inches of new snow. Winds have been relatively light over the past few days and this has limited unstable slab formation to local features or isolated slopes or pockets, mainly near ridges at higher elevations. Periods of strong sun and warming caused some natural or triggered loose or wet loose slides on sun exposed terrain Friday. These slides were limited to the most recent snow of 4 to about 8 inches. The significant snowfall received through mid-March amounting to 3 to 7 feet or more has continued to settle and consolidate over the past week. There have not been any recent deeper slides releasing to these older snow layers. There was one isolated slab release last Sunday of about 3 to 4 feet near Blewett Pass that released down to a crust-facet layer, likely MLK or early February crust region. This slide could have possibly been triggered remotely by a nearby party or possibly natural. There were extensive large slides during the mid March storm cycle, but none known of since this one event last Sunday. As spring unfolds, daytime warming and sun periods are allowing surface melt-freeze crusts to form on most southeast to southwest slopes. On steeper shaded north slopes settling and generally stable powder can still be found, especially wind sheltered terrain away from ridges. The main current avalanche concerns should be any recent wind deposited snow layers, mainly isolated to terrain features on northwest to northeast facing slopes at higher elevations and near ridges... large recent cornice formations along ridges as these likely will weaken during any daytime warming periods. Also, possible loose or wet snow slides on some southerly aspects, especially if receiving sunshine for the first time after recent snowfall. Finally, there still remains the potential for some isolated deeper avalanches down to crust/facet layers from February or January. Snowmobile access skiers in the central WA Cascades, Salmon Le Sac area on Thursday were concerned about these old crust-facet layers and before exposing themselves on steeper terrain probed many areas from 6 to 7000 feet. The weakness at this crust region was evident and they proceeded to chose more conservative terrain as a result. The layer in that areas was generally 6 to 7 feet below the surface. Detailed Forecasts Saturday and Saturday night Light to moderate snow showers should gradually move across the area from south to north through the day Saturday. Any new snow is expected to fall with relatively light winds in most areas. Therefore only a slight increase in danger is expected, mainly near ridges or terrain features where local winds may be stronger, thus building some shallower denser wind deposits, likely west to northwest facing slopes at higher elevations. Thus, increasing caution is advised on this more shaded terrain where shallow unstable wind deposited layers are possible. Sunday and Sunday night Another weak frontal band is expected to follow a similar path and move northward across the area Sunday. This should also have generally light winds and only slight warming. The main concern would be for any local wind slab formation, though this should be isolated to open slopes near ridges at higher elevations and some terrain features. Any new snow may also quickly become unstable due to sun or daytime warming during any breaks between showers, mainly late Sunday. Gradual clearing overnight should allow for surface crust formation on many southerly aspects and allow for further slow consolidation of recent snow on shaded slopes.