Avalanche Forecast

Issued: Jan 30th, 2017 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is low. Known problems include Deep Persistent Slabs and Wind Slabs.

tim haggarty, Parks Canada

Banff Yoho Kootenay.

Just how sensitive the snowpack is to a trigger became quite clear this weekend when the winds picked up. Fresh windslabs have formed and the slab over the weak midpack has developed further. Cautious terrain selection has become even more important

Summary

Weather Forecast

The jet stream that has been directly over our heads for the last few days will shift further south tonight. Cold northern air will return with north winds at upper elevations and plunging temperatures pushing away some remaining cloud and moisture. Clear, Calm and Cold by Wednesday night. This state of affairs looks to last until Friday.

Snowpack Summary

Strong to Extreme S and W winds continue to redistribute the 5 to 10 cm of new snow and the 10 to 20 cm that fell last week. Isolated surface hoar may be found buried in sheltered locations. Generally the midpack is weak at TL and above and the entire snowpack is weak BTL. Near the divide, deeper snow-packs are a bit stronger and more supportive.

Avalanche Summary

There is evidence of a avalanche cycle over the weekend and continuing today with windslabs and a few larger events involving the midpack / basal layers. Most of these events could be attributed to the wind redistributing recent snowfall and speak to the fragile nature of the snowpack: it required only small inputs to generate natural avalanches.

Confidence

Due to the number of field observations

Problems

Deep Persistent Slabs

The snowpack is weak. Slopes where a slab sits over the deeper weak layers should be treated as suspect. Avoid steep slopes with this structure. Continued conservative choices will remain important for some time.

Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Strong to extreme South and West winds combined with 5 to 10 cm of new snow continue to form slabs in lees areas Monday. These are likely to remain reactive for some time after the winds abate

Use caution in lee areas. Recent wind loading have created wind slabs.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 31st, 2017 4:00PM