Northwest Avalanche Center Backcountry Avalanche Forecast West Slopes South This product is expired This text version is archived in relation to a fatal accident on this day in this forecast area Issued Friday, December 10, 2021 - 6:00PM Expires Saturday, December 11, 2021 - 6:00PM Author Andy Harrington THE BOTTOM LINE If you venture into the mountains on Saturday, expect to be battling a potent winter storm and dangerous avalanche conditions. Red flag signs of instability such as recent avalanches, whumpfing collapses, or shooting cracks should steer you away from slopes over 35 degrees. Choose conservative terrain and realize that early season conditions still exist. Avalanche Forecast Avalanche Danger - Saturday, December 11, 2021 Above Treeline Considerable (3) Near Treeline Considerable (3) Below Treeline Moderate (2) Avalanche Problem #1 Storm Slab Aspect/Elevation: All Likely Small (D1) to Large (D2) Look for Storm Slabs to develop on Saturday at all elevation bands as the West South is targeted by a potent winter storm. These slabs will be thicker and more reactive as you ascend in elevation or in wind-loaded terrain, particularly on the volcanoes where more impressive water numbers are expected. Multiple storm layers and density changes are expected to exist above the Late November Crust, so use test slopes and hand pits as you travel to look for layers of concern. If you find heavy snow over light snow, see recent avalanches, or notice shooting cracks or blocks of snow failing in your tests, avoid slopes over 35 degrees. Forecast Discussion Snow depths have slowly increased since 12/8 around the West South, and Saturday should be the biggest dump of snow the zone has seen this season. The depth of the snowpack could double in some locations by the end of the day on Saturday, greatly expanding the amount of terrain where avalanches can occur. At Paradise, a whopping 3" of precipitation is forecast to fall by Saturday evening, which could produce more dangerous avalanche conditions than areas closer to the crest (where we are expecting ~1.75" of water). Regardless of location or elevation, new snow will thicken the depth atop a firm base we are calling the Late November Crust. Any layers of concern will exist above this easily identifiable layer going forward. Keep in mind that despite the new snow, early season conditions still exist. Open creeks, rocks, stumps, and other natural hazards that may have been visible on Friday could be just buried under the surface on Saturday. Take it slow and ease into winter, we are just getting started. "Uphill travel reminder: Check in with your local ski area this weekend regarding terrain access and parking updates. Closed ski areas often share a similar snowpack and avalanche hazard as the surrounding backcountry. You may also encounter other hazards like active avalanche mitigation, unmarked obstacles, snowmobiles, groomers, and other heavy equipment as ski areas prepare to open. Be prepared to make your own assessments and handle emergency situations." Weather Forecast: Increasing heavy snow at Paradise becoming very heavy overnight. Light snow becoming heavy overnight at Crystal. Increasing light to moderate snow at White Pass. Strong ridgeline winds. Very heavy snow at Paradise tapering to moderate snow in the afternoon. In other areas, heavy snow in the morning tapering to moderate snow (White Pass) and light snow (Crystal) in the afternoon. Decreasing strong ridgeline winds in the morning. Precipitation (WE): Crystal Mt 1.00 " 0.75 -1.00 " This information is provided by the U.S.D.A. Forest Service and describes general backcountry avalanche hazard and conditions. It does not apply to ski areas and highways where avalanche mitigation is conducted.