The wind slab problem is fairly widespread on the Northern half of the compass above 7000 feet. Wednesday we were able to intentionally trigger a decent size example of this problem below a cornice on a NE facing slope that was still being actively loaded. We also observed several areas on the steep, northerly terrain in the Hum Lake area that failed on their own. Last weekend we had skier triggered avalanches reported on very high, wind loaded western aspects. Yesterday, we toured the ridgeline above Josephine Lake and saw fewer natural avalanches in that area but found the effects of the wind to be highly variable with a punchy, wind crust/board resting on a layer of well developed faceted snow on a shallow, rocky, upper elevation SW facing slope. This layer collapsed under the weight of our skis and also provided one small but notable whumph where it was resting on a deeper snowpack. We also found several small "pockets" of cross loaded wind slab on E and SE terrain at the ridgetop. Overall, you can look at windloaded terrain right now with the great visibility and see the warning signs: rounded, pillowy, sculpted terrain is the norm throughout the Northerly terrain, and these features are pretty much yelling "leave me alone" right now.
With the upper elevation temperatures climbing above freezing in the afternoon yesterday, we saw signs of change in the snowpack on the southerly or solar aspects. Roller balls started picking up around 2 pm with trees shedding snow and rime at the same time. If today proves to be sunny and warm again in the upper elevations, watch for an increase in the potential of loose wet slides later in the day. We saw a few small point release slides on sunny, rocky terrain yesterday and a good specimen on Osprey Point as we were driving back in on Warren Wagon.
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We found a variable snowpack yesterday near Josephine Lake on Squaw Point. Aside from the obvious wind slab build up with the last storm cycle, we found an average of about 55 cm or 21 inches of settled snow from the storm cycle earlier this week. The aspects that we tested yesterday were pretty similar in that we had moderate Compression Test failures in the upper 1/3 of the new snow with irregular fracture planes which lacked propagation potential. Closer to the interface with the older snow near 55 cm down we had a cleaner, Q2, SC failure that broke in the hard range(CT 25) on both aspects. The mid pack has become very strong and well consolidated over the last 2 weeks but still shows a high degree of variation where it is shallow or deeper with a fairly uniform layer of rounding facets and a reverse density(denser snow above weaker snow) change in the lower 5 to 20 inches of the snowpack. We found very well developed depth hoar forms on a shallow rocky area with an unsupportable wind layer overlying them.
In addition, we noticed that the sun and heat began to change the snowpack mid afternoon with trees beginning to shed and a few small point releases kicking off in steep rocky, sun affected terrain. On our way back to town we also saw a nice slab on the rocky slopes of Osprey Point that started as a point release on shedding rocks and was able to propagate into a shallow slab on the slope below.
SHORT TERM...Inversion forming as temps aloft rise while snow- covered surface gets gradually colder. Fog has formed during the night in the valleys. As the inversion gets stronger and shallower the fog should eventually find its way to the lower Treasure Valley...Saturday or Sunday. Otherwise, continued dry and cold with light winds.
LONG TERM...Saturday night through Friday...An upper level ridge will keep our CWA dry through Monday, and possibly Monday night as well. But an unsettled pattern will return starting Tuesday, as a long fetch of moisture from across the Pacific reaches our area. After Monday we can expect precipitation each day, with most falling Tuesday through Thursday, mainly in the form of snow. A mix of rain, freezing rain, and snow is also possible, as mild and moist Pacific air flows over the top of the cold air anchored in the valleys. Temperatures will slowly moderate, from around 15 degrees below normal on Sunday to around 5 degrees below normal by Friday.
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.