Wind slab will be the main concern for the forecast period. Watch for reactive wind slabs in lee and cross-loaded terrain features at upper elevations. Beyond Sunday, we have uncertainty regarding the effect of warm temperatures and possible wet precipitation on the snowpack, so make observations and assess conditions as you travel.
Watch for fresh wind slabs in new terrain features as winds switch from northwest to northeast on Sunday. Wind slabs may be especially reactive where they sit over a crust which makes a slick be surface for avalanches. Watch for shooting cracks as an indicator of reactivity in wind-stiffened snow.
Cornices have grown with recent moderate winds. Cornice falls can be dangerous on their own and they can also trigger wind slabs on slope below. Give them a wide berth when travelling on or below ridgetops.
Wind slab avalanches size 1-2 were observed prior to the weekend on north to east facing slopes in the alpine. Some of them are suspected to have been triggered by cornice falls.
Recent snowpack test results and signs of instability like shooting cracks reported in recent MINs also suggest instability in wind slabs.
Variable snow conditions exist at upper elevations due to extensive wind affect by sustained moderate west to northwest winds. Soft snow can still be found in sheltered areas like in trees, gullies and bowls.
A widespread near-surface crust has been described in nearly every MIN report this week (thank you!). It sits on the surface in scoured, windward features; an average of 10 cm deep in sheltered areas; and up to 30 cm deep in wind-loaded areas. Some faceting has been observed above the crust which has created a weak layer for overlying wind slabs to fail.
The snow below is a mix of dense wind affected snow layers at higher elevations. At lower elevations you may find another thin melt freeze crust 50+ cm deep. The lower snowpack is likely dense and well bonded from warm temperatures, rainfall and subsequent refreezing.
Saturday night
Flurries bringing a few cm of new snow. Moderate to strong northwest wind. Alpine temperature -10 to -15 C.
Sunday
3-8 cm of new snow. Moderate to strong northwest wind, switching northeast later in the day. Temperatures warming through the day, possibly reaching 0 C by evening.
A "backdoor warm front" pattern associated with a series of atypically tracking low pressure centers moving west-to-east is casting great uncertainty on the weather forecast beyond the weekend. The following outlook is from the 12Z RDPS model run but large variations from one run to the next give us low confidence. Generally, this pattern will likely bring strong easterly to northeasterly wind, warm air and the possibility of mixed precipitation.
Monday
A mix of sun and cloud. Moderate to strong easterly wind. Alpine temperatures dipping back below zero to around -5 C.
Tuesday
Increasing cloud with a possibility of mixed flurries. Strong northeast wind. Alpine temperature around 0 C.
More details can be found in the Mountain Weather Forecast.
