Avalanche Forecast
Issued: Jan 4th, 2021 8:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Cornices and Persistent Slabs.
Jonas Hoke,
Natural activity has tapered off, but skier triggering of recently developed slabs remains likely.
If wind and snowfall pick up earlier than forecast this afternoon, overhead hazard will once again become a concern.
Summary
Weather Forecast
A spike in wind, temps, and snowfall will accompany a front passing our area late this afternoon.
Today: Flurries (7 cm). Alpine High -3 C. Ridge wind light (increasing to strong late in the day) SW. Freezing level (FzL) 1600 m.
Tonight: Flurries (7 cm). Low -11 C. Moderate SW wind.
Tuesday: Mainly cloudy. High -9 C. Light S wind.
Weds: Snow (15cm)
Snowpack Summary
60cm of snowfall over the weekend was accompanied by strong to extreme winds from the SW. A surface hoar layer, buried Dec 26, may be preserved in sheltered areas at and below treeline, down 70+cm. The Dec 13 surface hoar can still be found down 120cm and the Dec 7 crust/facet/surface hoar (aspect/elevation dependent) layer is down 135+cm.
Avalanche Summary
There was widespread large natural avalanche cycle Saturday through early Sunday morning.
Artillery control Saturday night produce numerous avalanches up to size 4, notably MacDonald West shoulder and Crossover resulted in deposits on the highway.
Control just West of the park on Sunday morning also produced avalanches to size 4 from a North aspect.
Confidence
Problems
Storm Slabs
Heavy snowfall over the weekend, accompanied by strong-extreme SW wind, has built thick storm slabs in all open terrain.
A Dec 26 surface hoar layer may persist below this slab in sheltered areas at treeline and below.
- The new snow will require several days to settle and stabilize.
- Use conservative route selection, choose moderate angled and supported terrain with low consequence.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Cornices have grown significantly this weekend and may be further tested as winds spike this afternoon. These could trigger the storm and persistent slabs below.
- Stay well back from the leeward side of corniced ridgecrests.
- Minimize overhead exposure during periods of heavy loading from wind.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Persistent Slabs
Avalanche activity this weekend shows that large triggers (such as cornices and storm slabs) could still cause very large avalanches on these layers.
- If triggered the storm slabs may step down to deeper layers resulting in large avalanches.
- Be wary of large slopes that did not previously avalanche.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 5th, 2021 8:00AM
