South Rockies Avalanche Forecast
Feb 13th, 2018 5:18PM
Wind slabs, cornices and persistent slabs make for a tricky situation out there. Ride in conservative terrain and avoid all overhead hazard to manage your risk.
Moderate - Forecast snowfall amounts are uncertain on Wednesday
Wednesday will see an upslope event bringing modest amounts of low density snow, with higher amounts on eastern slopes. TUESDAY NIGHT: Flurries (5-10cm of low density snow). Winds moderate gusting strong from the north west. WEDNESDAY: Flurries (5 -15cm accumulation). Ridge wind moderate gusting strong from the north / west. Temperature -7. Freezing level valley bottom.THURSDAY: Sunny with cloudy periods. Ridge wind gusting moderate from the west. Temperature -9. Freezing level valley bottom.FRIDAY: Isolated flurries. Ridge wind becoming strong from the southwest. Temperature -5. Freezing level 1000m in the afternoon.
On Tuesday we received reports of size 3 avalanches, likely from the weekend and likely triggered by cornice fall. See here for the MIN report. 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.
Wind has been the main weather story over the past few days, with gusts on Tuesday over 130 Km/ hr!The end result is extensive scouring on windward slopes (generally north and west facing slopes) and the creation of wind slabs on down wind (lee) features higher up, on a wide range of aspects. The lower snowpack in this region is weak, with two main concerns: A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 100-150 cm deep. Second, 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 weak layers are still active and deserve a lot of respect. The solution is to stick to conservative terrain while avoiding all overhead hazard.
Strong to extreme winds 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.
Use extra caution as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.
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.
Extra caution needed around cornices with current conditions.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Be aware of the potential for large, deep avalanches.
Cornices have triggered very large avalanches recently. Be especially wary of long runout distances in avalanche paths, and the possibility of mature timber being taken out by a surprisingly large avalanche.
Avoid steep slopes below cornices.Give cornices a wide berth when traveling on or below ridges.
Valid until: Feb 14th, 2018 2:00PM