Avalanche Forecast
Issued: Jan 30th, 2021 1:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet, Persistent Slabs, Wind Slabs and Storm Slabs.
Ryan Shelly,
VIAC
See below for Confidence details:
Avalanche Summary: Several size 1 and size 2 natural slab avalanches have been reported over the week. Several size 0.5 to size 1 skier triggered avalanches also reported.
Confidence details tab is currently under maintenance- posting Confidence details here:
High confidence: Based on extensive data collection all week as well as many people submitting observations from the field. Monday's confidence is Moderate.
The elevated avalanche danger ratings (for the next 3 days) is as a result of strong precipitation and winds forecasted for the region.
Tree well hazards will increase substantially this weekend as a result of the major amounts of snowfall expected for the region. Keep an eye on your riding group and ride in pairs.
This forecast brought to you by forecaster's Dave Kallai and Ryan Shelly
Summary
Past Weather
New snow, cold temperatures and some wind effect have made for outstanding snowmobiling and skiing/snowshoeing since the storm’s arrival several days ago. As a result of all the new snow, it appears that avalanche activity is occurring within the upper 20 cm to 50 cm of the upper snowpack. Expect this problem to increase as additional new snow arrives to the forecast area this weekend.
Weather Forecast
The next weather front is expected to arrive on Friday evening with strong to moderate winds. Expect the weather to become a bit more aggressive as strong winds and strong precipitation rates arrive Saturday, January 30th. Light precipitation for the East and North end of the forecast region while the West and South end of our bulletin area stand to receive substantial snowfall amounts.A strong Northwesterly flow will arrive on Friday evening. This frontal system will bring warm air and deliver strong southeast winds and precipitation rates.Saturday 20 cm Snow for the North island and 50 cm Snow for the South and mid-island, Moderate winds gusting to strong from the Southeast, Freezing level 750MSunday: (5 cm Snow North island) and (30 cm Snow South and mid-island), Moderate winds gusting to strong from the Southeast, Freezing level 850MMonday (5 cm Snow North island) and (10 cm Snow South and mid-island), Moderate winds from the Southeast, Freezing level 900M
Terrain Advice
Keep to simple terrain (terrain under 30 degrees slope angle) and utilize small slopes to test the reactivity of the recent snowfall.Keep an eye on snowfall rates, wind transport and rising temperatures for your area, as this promotes slab formation and “touchy/easily triggered” conditions.Be cautious when route-finding and transitioning from scoured areas into areas of wind loaded snow.Avoid open and steep slopes during periods of warming and rain. A small loose wet avalanche will entrain and gain enough mass to push a mountain traveller into gullies and over cliffs.Avoid travelling above or below cornices and keep to conservative decision-making.
Snowpack Summary
Over the week, 5-20 cm of snow fell and was transported by southeast winds creating soft slabs in the current affected areas. This overlies a sandwich of supportive melt-freeze crusts within the upper 60-80 cm of the upper snowpack. Below this, the snowpack is well settled.
Snowpack Details
- Surface: Wind distributed soft slab or low, dense snow on the crust.
- Upper: 20 to 50 cm below the surface exists a melt-freeze crust with facets (PWL) resting above this crust.
- Mid: Generally, well settled with several melt-freeze crust layers
- Lower: Well, settled and well bridged and includes a 10 cm thick layer of large facets
Confidence
High -
Problems
Loose Wet
Above zero degrees air degrees air temperature and precipitation in the form of rain will rapidly decrease the stability of the upper snowpack.
Location: Widespread All aspects and at below treeline elevation band.
Possibility: Triggering of this avalanche problem is “Very Likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “likely.”
Size: If triggered, expect these avalanches to be small but will entrain and could become large up to size 2 with enough mass to bury, injure or kill a mountain traveller.
Likelihood
Expected Size
Persistent Slabs
We haven’t seen any activity, but we are still concerned about our two persistent weak layers (PWL), forming our persistent slab problem. Since this layer isn’t currently reactive to skier traffic, the likelihood may be low. However, this layer is deep in the snowpack, and with an increased load like a cornice fall, it could trigger a large avalanche.
Location: Found at all elevation bands and on multiple aspects.
Possibility: Unlikely to Possible from natural and human triggers.
Size: If triggered, expect these avalanches to be large enough to bury a person (size 2-3).
Likelihood
Expected Size
Wind Slabs
The recent winds have produced Wind slabs that can be found predominantly in North aspects. This wind slab overlies either a thick crust or a surface hoar layer, making it unstable. Friday night, we are expected to see moderate and gusting to strong Southeast winds with the approaching storm's onset.
Location: Northeast to Northwest alpine and treeline features.
Possibility: Triggering of this avalanche problem is “likely to very likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” to “likely” depending on the elevation band.
Size: If triggered, expect these avalanches to be large enough to bury a person, size 2.
Likelihood
Expected Size
Storm Slabs
New storm slabs will form and be present on terrain that is not exposed to the wind.
South Island: Wet slabs are expected during periods of rain. Expect the slab sensitivity to triggering and propagation to increase as temperatures increase.
Mid and North Island: Slabs are expected to be the deepest with forecasted precipitations amounts of 10-50 cm.
Location: Widespread on aspects and at all elevation bands Saturday and Sunday.
Possibility: Triggering of this avalanche problem is “Very Likely” from light loads such as skiers, snowshoers and snowmobilers. Natural avalanches are “possible” depending on the elevation band.
Size: Size: If triggered, expect storm slab avalanches on specific terrain features to be large, size two and on isolated features very large size 3.
Likelihood
Expected Size
Valid until: Jan 31st, 2021 1:00AM
