South Rockies Avalanche Forecast
Feb 10th, 2018 4:38PM
Many large destructive avalanches released full depth and ran full path recently. Avoid all avalanche terrain, free from overhead hazard. Special Avalanche Warning in effect. Copy this address to view details: http://bit.ly/2nSOUyX
Low - Due to the number of field observations
We're looking at cool temperatures and some light flurries for Sunday. Overnight lows will be near -20 Celsius at tree line. SUNDAY: Flurries Saturday overnight through to Sunday afternoon with up to 10cm accumulation of low density snow. Ridge wind moderate gusting strong from the east. Temperature -15. Freezing level valley bottom.MONDAY: Mostly sunny. Ridge wind light, northwest. Temperature -12. Freezing level valley bottom.TUESDAY: A mix of sun and cloud. Ridge wind strong from the west. Temperature -9. Freezing level 1100m.
A widespread natural avalanche cycle occurred Thursday afternoon and overnight into Friday. Several storm slabs and deep persistent slabs to size 4 were reported when visibility improved on Friday. See this MIN post for more information. These avalanches are failing on weak layers deep in the snowpack and running to valley bottoms. See this video for more details. On Wednesday, naturally triggered deep persistent slab avalanches up to size 2.5 were reported in the Alexander Creek Drainage. The suspected failure layers were mid-December or late-November layers near the base of the snowpack. Also avalanche control in the Line Creek area produced several size 2.5 and two size 3 avalanches that also failed on weak layers near the base of the snowpack. A week ago in the neighboring Lizard Range, the east facing Mt Corrigan slide path produced a very large natural avalanche estimated to be a size 4.0, which took out mature timber in the path as it overran the Flathead FSR south of Corbin.
20-40cm of snow fell on Wednesday into Thursday, bringing storm snow totals to 50-90 cm over the past week. The distribution of this new snow is highly variable. The western parts of the region in BC were relatively warm with less snow, while areas in Alberta and around the divide were much colder and windier. The lower snowpack in this region is weak, with a number of concerns: A layer buried mid-January is composed of surface hoar on sheltered aspects and a sun crust on solar aspects is now 60-80 cm deep. Another surface hoar layer from early-January is buried 70-90 cm deep. A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 100-150 cm deep. Finally, a rain crust with sugary facets buried in late-November is near the bottom of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.The take home message is that several weak layers are still active and deserve a lot of respect. The solution is to stick to conservative terrain while avoiding all overhead hazard.
New snow and strong wind have formed touchy slabs, especially at higher elevations and in wind-exposed terrain. Wind slabs may step down and trigger deep persistent weak layers, resulting in large destructive avalanches.
Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use extra caution as you transition into wind affected terrain.
Deep Persistent Slabs
Several deeply buried weak layers have the potential to produce large avalanches reaching run out zones. Cornices have been a recent trigger for very large avalanches. Avoid shallow rocky snowpack areas where human triggering may also be possible.
Be aware of the potential for large, deep avalanches.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Extra caution needed around cornices with current conditions.
Valid until: Feb 11th, 2018 2:00PM