While there has been markedly less avalanche activity this week in this zone of the forecast region, avalanche control in Yoho today still produced several slabs on the deep persistent layer.
Factor in the effects of rising freezing levels and solar inputs as you select your objectives this weekend.
The avalanche problems described will become more sensitive to human triggering as the snowpack warms up and the potential will increase for snow to move as cornice failures or small solar triggered events which could initiate these slabs as well.
20 to 30cm fell during the storm to bury a layer of surface hoar, facets and sun crusts on March12. Isolated pockets of wind slab were also formed near ridge crests. Following the end of the storm we have seen limited amounts of activity on this layer however it has been around long enough, and raises enough concern, to now be classified as a persistent slab.
Three persistent weak layers formed in January are down 60-120 cm. Buried sun crusts on steep solar slopes present the greatest concern for triggering, however, weak facets and isolated surface hoar can be found on the same interfaces on shaded aspects.
The weak depth hoar at the bottom of the snowpack inspires little confidence. We have seen increased activity on this layer through the week in most areas of the forecast region with the exception of the deeper snowpack areas around Little Yoho. Give careful consideration to the slopes overhead as large avalanches may run well into the runout zone or into lower-angle terrain. Avoid big terrain features and be especially cautious in thin or rocky areas, where triggering is more likely.
Avalanche control on Mt Field produced mixed results with some shallow slabs while other slabs stepped down to the ground up to sz 2.5. Low targets of Mt Stephen produced avalanches on every shot but these did not exceed sz 1.5. On Mt Dennis shots again triggered slabs to the ground up to sz 2.5.
20-30 cm of snow buried a layer of surface hoar, facets and sun crust on March 12. Suncrusts are forming on steep solar slopes.
The midpack comprises various Jan crust layers that are now down 60-120 cm.
The weak Nov. 16 basal facet layer is down 90-190 cm.
The region will continue to sit under the influence of a high pressure system until late on Sunday. Heating will be the most significant weather influence to the snowpack for the period.
Sunday, the winds should be very light. Freezing levels will reach to near 2000m and solar heating may bring temperatures to peak values, however, as the ridge breaks down some convective activity can be expected in the afternoon which may curb heating. Overnight, a trough will bring increasing cloud cover and flurries.
Monday up to 5cm of snow may be possible with freezing levels reaching to about 1600m.
