Avalanche Forecast

Issued: Mar 30th, 2014 8:47AM

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

South Columbia.

Periods of sun over the next few days will increase the danger on south facing slopes. 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 build on Monday and should persist until at least Wednesday. A weak disturbance may cross the region on Wednesday resulting in increased cloud cover and isolated light showers. Monday: A mix of sun and cloud, freezing level am: 1100m pm: 1600m, ridgetop wind: light SW-WTuesday: Mostly sunny, freezing level am: 400m pm: 1800m, ridgetop wind: light NWWednesday: A mix of sun and cloud, freezing level am: 600m pm: 1800m, ridgetop wind: light SW-W

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 was a natural size 3 in the Cariboo region on Thursday. The S Columbia had one step down on Tuesday and the N Columbia on Monday. While these layers are typically dormant, they are expected to become reactive again with the new loading or the upcoming strong solar inputs.Reports from Saturday for the South Columbia include isolated natural and human triggered avalanches up to size 2 in the recent storm snow down 20-30cm. Loose sluffing from steep terrain features was also reported.

Snowpack Summary

New storm snow has formed a soft slab which is typically 20-30cm thick. On south aspects, the storm snow overlies a sun crust, but due to recent warm temperatures, the layers are generally bonding well. In isolated areas, the storm slab is reported to be quite reactive to triggering. Stiffer wind slabs may exist in immediate leeward features on NW through E aspects.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 is still reactive to human triggers. Stiffer wind slabs can be expected on leeward features on NW through E aspects. Sun will increase the reactivity of the storm slab and loose activity is expected from steep, sunny slopes.

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

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.

Be aware of thin areas that may propogate to deeper instabilites.>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.>Avoid large convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

3 - 7

Valid until: Mar 31st, 2014 2:00PM