Winds out of the south, southeast and southwest hammered the West Central Mountains through the second half of last week. Wind gusts were in the 40-60 MPH range on the higher peaks and ridges with sustained winds in the 20+range. These strong winds did a great job loading and crossloading slopes on east, north and west facing aspects as well as loading slopes below rocky or steep headwalls well below the ridgetops. Windslabs range from very stiff to soft today and from a few inches to over a foot thick. Some of these windslabs formed on the crusts that developed during our last high pressure. Look for clues like cracking and collapsing as well as other obvious signs of windslab like a textured or scalloped snow surface or pillows and drifts as you are moving through the mountains today. Additional snowfall on Friday evening also did a great job camouflaging some of these obvious clues so pay attention to the way the snow feels as you travel today, if you encounter a hollow, punchy, or drummy feeling snow surface you are on windslab. Snowmobiles may have more of an affect on these slabs than skiers where they are more dense or firm. Wind slabs often let you get well out on to them before you are able to trigger them trapping you in the middle of the slab when it is triggered.
Natural R1/D1 windslab avalanche triggered by a failing cornice on a NNW slope near Pearl Lake 2/23/16:
With temperatures climbing back into the mid 40's over the next few days and mostly sunny skies, we can expect a rise in loose/wet, roller ball and point release avalanche activity on steeper aspects affected by the sun and rising temperatures. The temps didn't quite get warm enough for these aspects to start shedding snow yesterday but the likelihood is increasing today with the temps and will continue tomorrow and Friday. In addition large cornices have developed on many northerly aspects this winter and have already begun to fail. Keep your eyes open for what is above you if you are on the shady side too. As the temps climb, more of these big cornices are going to fail as well. When the temperature climbs, you will need to find cooler slopes or call it a day.
Ladies, Don't forget about our Diva Avalanche Class this weekend at Tamarack Resort. Show up early for yoga and coffee or come just for the class. Stay late for Happy Hour at Seven Devils Pub! Register by clicking on the class for more info. Suggested donation of $10 for the Friends of the Payette Avalanche Center.
We traveled into Marge Lake yesterday to check out a natural avalanche that occurred on Friday last week yesterday. The slide occurred on a a windloaded NNW aspect and looked like it failed early Friday and had a few inches of new snow on top of the debris, based on its size relative to the path or slope it would be classified as R2/ D 1.5-2 because of its potential to bury a person and the amount of debris. We saw a couple of other small avalanches(R1/D1) on nearby NNW slopes that were newer and looked like they failed in shallow wind slabs that were triggered by falling cornices above.
Based on our stability tests and lack of recent avalanche activity associated with the buried surface hoar layer over the last 3 weeks, we are phasing the deep slab/persistent weak layer problem out of the advisory for now. If (or when) temperatures allow melting water to percolate through the snowpack we could see this particular bogeyman make another visit to the West Central Mountains. Keep this layer in mind if you are skiing or riding on protected Northerly slopes with a steep, shallow snowpack because you could still be unlucky enough to find a trigger point for a large and unsurvivable avalanche on the wrong slope even though the chances are low.
Expect mostly sunny conditions with some high clouds today. Temperatures will begin to rise today and continue through Friday with some of the warmest temperatures of the year forecasted for tomorrow and Friday. A strengthening Inversion will keep lower elevation temperatures slightly cooler as the mountains warm to 8-12 degrees above normal for this time of the year. A shortwave trough will enter the Pacific NW on Friday with increasing precipitation on Friday night and through the weekend. Based on temperature models, a raincoat or umbrella may be a safe bet on Saturday...
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.