Avalanche Forecast

Issued: Mar 31st, 2014 9:27AM

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

rbuhler, Avalanche Canada

Cariboos.

Danger will increase on south facing slopes during afternoon warming. Solar radiation could be enough to trigger stubborn persistent slabs or cause cornice failures. Conservative route selection remains crucial at this time.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure will keep the Cariboos sunny and dry for Tuesday. Unsettled conditions are expected for Wednesday and Thursday resulting in a mix of sun and cloud with localized convective flurries.Tuesday: Sunny, freezing levels am: surface pm: 1400m, ridgetop wind: light W-NWWednesday: A mix of sun and cloud, light scattered flurries possible, freezing levels am: 400m pm: 1500m, ridgetop wind: light SW-WThursday: A mix of sun and cloud, light scattered flurries possible, freezing levels am: 1000m pm: 1800m, ridgetop wind: increasing to moderate S-SW during the day

Avalanche Summary

A low probability, but high consequence avalanche problem plagues the Columbia regions. These highly destructive and largely unpredictable avalanches are expected to be isolated, but certainly possible anywhere at any time. Avalanches continue to step down to old, deep weak layers. The most recent were natural size 3 avalanches in the Cariboo region on Sunday and on Thursday. The S Columbia had one step down last Tuesday and the N Columbia last Monday. While these layers are typically dormant, they may become reactive again with strong solar radiation input.Reports from Sunday include a natural size 3 stepping down to the early-February layer on a NW aspect and a natural size 2.5 storm slab avalanche. Also reported from the weekend was a remotely triggering size 2 slab avalanche that released down 100cm.

Snowpack Summary

The weekend storm snow typically produced 30-40cm of new snow. Reports suggest moist snow up to 1800m on all aspects and higher on south facing slopes. Stiffer wind slabs may exist in immediate leeward features on NW through E aspects in exposed terrain in the alpine.Three persistent weaknesses contribute to a highly variable, fundamentally unstable, complex snowpack with step-down potential. The mid-March sun crust/surface hoar layer down 50-80cm still has potential for human-triggering in isolated areas. The early-March crust/facet/surface hoar layer down around 80-120cm has become less susceptible to human-triggers, but still has the potential to produce large avalanches, and we continue to see fractures stepping down to this layer. The mid-February crust/facet/surface hoar layer is typically down at least 1.5m and direct triggering has become unlikely. However, large loads like cornices or smaller avalanches stepping down can still trigger this layer and produce very large avalanches.

Problems

Storm Slabs

Recent storm snow may still be reactive to human triggers. Stiffer wind slabs in lee features may be more sensitive to triggering. Sun will increase the reactivity of the storm slab in the afternoon and loose activity is expected from steep terrain.

The new snow will require several days to settle and stabilize.>Minimize exposure to sun exposed slopes when the solar radiation is strong.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Weaknesses buried earlier this month remain reactive to light triggers in isolated areas (convex slopes, southern aspects, and higher elevations). Step down potential to deeper persistent weaknesses can result in highly destructive avalanches.

Minimize exposure to sun exposed slopes when the solar radiation is strong.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Deep Persistent Slabs

Isolated highly destructive avalanches are expected to continue. But beware, the variable nature of this problem makes it difficult to predict exactly when and where avalanches are going to occur. Sun and warm temperatures may 'wake-up' this layer.

Avoid large convexities or areas with a thin or variable snowpack.>Resist venturing out into complex terrain, even if you observe no obvious signs of unstable snow.>Local knowledge of slopes that have yet to avalanche is valuable for knowing which slopes to avoid.>Be aware of thin areas that may propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Apr 1st, 2014 2:00PM