Winds increased throughout the day yesterday and overnight. S and SW winds over the last 48 hours combined with some wet snow and rain have created some dense new windslabs throughout the local mountains. Some of these slabs have formed on a rain crust from last weekend's rain event which will increase the hazard and likelihood of triggering the slab. In the higher terrain, there was also a layer of unconsolidated dry snow above the crust which will help to lubricate the crust/ windslab interface and created a slightly upside layer below the wet snow that accumulated Thursday and yesterday. Steep leeward, windloaded slopes should be avoided or only approached after careful snowpack assessment. Crossloading will likely have occurred as well on East and West aspects as well as the winds were predominantly out of the South earlier this week. Winds will be increasing throughout the day today and tonight and accompanied by 3-7 inches of new snow. Expect the windslab problem to continue to increase as the slabs get thicker and more dense with more snow today. Cracking, hollow or punchy snow, drummy sounds, a sculpted snow surface, thick pillows, and scoured areas are all clues that should help you recognize wind slab problems.
Yesterday, we saw widespread roller ball activity at almost all elevations. We didn't see anything more substantial in the way of wet slabs or some of the larger point release wet slides we saw earlier in the week. Use caution if you are riding or skiing on steeper, wind protected terrain until the snowpack has a chance to refreeze, especially in the mid elevations. This process has already started in the upper elevations and will likely take a few days despite the low overnight temperatures forecasted with the coming cold front. As the new snow accumulates take the time to see how it is sticking to the older, wet snow or crusts below. The good news is we hopefully won't be talking about wet snow conditions over the next few days!
Yesterday we rode out of the upper elevation lot and looked at the snowpack from Brundage Reservoir all the way out to Hazard Creek Drainage and Headwaters. 2 days of rain definately left their mark on the snowpack with pretty horrible backcountry skiing conditions. A light crust had already formed on the snow surface yesterday morning as overnight temps on Thursday cooled for a few hours. Rain and increasing temperatures softened the crust and did little to improve conditions. Gusty SW winds picked up and in the upper elevations snow was falling by mid afternoon. Below 7000 feet rain was the precipitation of the day. The snowpack is surprisingly strong considering it has not had a good freeze for more than 4 days. Last weekend's rain crust is doing a good job keeping the liquid water in the snowpack from penetrating below it. The new snow above the crust is bonding well on lower angle slopes and most of the instabilities are confined to the 25-30 cm of new snow above the old crust. Conditions will be changing today with widely scattered snowfall in the mountains, decreasing temperatures and a good amount of accumulation accompanied by strong winds. Watch out for growing windslabs and a sensitive new storm slab if you are in the upper elevations today.
The upper elevations picked up a couple of inches of new snow yesterday afternoon and overnight. The rainline yesterday was right around 7000 feet. Expect scattered snow showers in the mountains today with increasing winds gusting to near 40 mph. A cold front and a substantial band of moisture will decrease snowlines tonight and bring a few inches of snowfall to the valley floor in McCall. Up to 1" of Snow Water Equivelant is predicted over the upper elevations over the next 48-60 hours with snowlines around 4000 feet. West facing slopes will be favored with up to a foot of snow predicted to fall on windward, upper elevation slopes. The cooler temperatures and active pattern of precipitation will continue through the week next week with near or below normal temperatures.
This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.