Avalanche hazard will increase throughout the day with additional wind transport and snow. Choose conservative terrain, avoid overhead hazard and check how the new snow is bonding to crusts and old snow surfaces.
Recent and ongoing snow & strong to extreme winds (southwest and southeast) are forming fresh storm slabs. Watch for fat deposits in leeward terrain features such as ridge crests and roll-overs.
Storm slabs may be particularly reactive where they accumulate over a weak layer such as surface hoar or a crust now buried 30-70 cm deep. The crust offers a slick bed surface for avalanches.
A series of fast moving frontal systems move through the region with precipitation and moderate to strong winds. The strongest storm arrives Friday thru Saturday.
Tuesday Night: Another 5-15 cm new snow, strong southwest ridgetop wind, alpine low -7 C, freezing level 1100 m.
Wednesday: Mainly cloudy with scattered flurries, 5-15 cm new snow overnight, light to moderate southwest ridgetop wind, alpine high -3 C, freezing level 1300 m.
Thursday: Mainly cloudy with flurries, 5-10 cm new snow, wind easing to light southwest, alpine high -5 C, freezing level 1300 m.
Friday: 15-30 cm new snow, wind increasing moderate gusting strong south, alpine high -3 C, freezing level 1200 m.
From Tuesday there were reports of isolated skier reactivity to size 1 at treeline in wind affected terrain below ridges and explosive controlled avalanches to size 1. There were limited alpine observations due to stormy weather. However, natural avalanches are expected with the recent new snow and strong to extreme southeasterly winds.
Where no slab properties are found, loose dry sluffing is being reported in steep terrain to size 1.
On Sunday, small natural and skier controlled size 1 loose dry and wind slab avalanches were reported running on the crust.
Have you been out and about in the mountains? If so please submit your observations to the Mountain Information Network (MIN). It doesn't have to be technical - photos are especially helpful! Thank you so much for all the great MINs submitted so far!
10-30cm of new snow fell by 3pm Tuesday with strong to extreme southeast winds in the alpine. Winds have scoured upslope features and redistributed snow in the alpine. By mid-morning on Tuesday 20cm of new snow were reported in this MIN by Round Mountain.
Another 5-20cm is forecast to fall overnight into Wednesday. As it falls, the new snow will continue to load lee features in wind exposed areas by strong to extreme southwest wind. Where wind sheltered snow is settling into a storm slab that overlies numerous interfaces.
A crust is now buried by 30-65 cm of snow at elevations above 1000 m. Prior to the new snow, the crust was punchy below 2000 m with a moist snowpack below. The new snow will likely help with bridging, and improve travel conditions. A MIN from Dec 14th at Sprout Mountain at 1550m found the crust reacting in snowpack tests. This crust was also reported in a "very easy" sudden character test pit (ECT) reported in this MIN at 1850m in the Flute/Russet/Fissile area on Dec 15.
In wind sheltered areas, the new snow may be falling on a layer of small surface hoar crystals. A second layer may also exist in close proximity below.
Snowpack depths change rapidly with elevation, with 0-50 cm below treeline to 170 cm in the alpine. Below treeline conditions are slowly improving but remain variable as indicated in this MIN from Singing pass trail.
