Avalanche Forecast

Issued: Mar 31st, 2016 8:42AM

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

rbuhler, Avalanche Canada

Northwest Inland.

A special warning has been issued for the substantial warming and sun this week. Deeply buried weaknesses within the snowpack are expected to wake-up and produce very large avalanches. It is best to avoid avalanche terrain during the heat of the day.

Summary

Confidence

Moderate

Weather Forecast

The ridge of high pressure is expected to break down on Friday as a weak frontal system reaches the coast. Friday should be sunny with alpine winds progressively becoming strong from the southwest and freezing levels progressively falling below 2000m. Cloudy conditions are expected for Saturday with moderate to strong southwest winds in the alpine and freezing levels dropping to around 1500m. A mix of sun and cloud is expected for Sunday with light to moderate southerly winds in the alpine and afternoon freezing levels around 1400m. A weak storm system is currently forecast to reach the region on Sunday night.

Avalanche Summary

On Wednesday, numerous slabs up to size 2.5 were reported on solar aspects in the far north of the region. Some of these releases were over 2m deep releasing on old weak layers. In the south, a natural icefall triggered a size 2.5 slab avalanche. Several loose wet avalanches were also reported. On Tuesday, widespread sluffing was reported at all elevations and well as some shallow solar triggered slabs up to size 1.5. Cornices and glide cracks are also reported to be very active in the north of the region. The continued warming, sun exposure, and limited overnight recovery means natural cornice releases, deep persistent slab releases, and loose sluffing are expected to continue on Friday. Very large avalanches will remain a serious concern until the region gets some sustained periods of cooling,

Snowpack Summary

A good overnight refreeze was reported in the south of the region on Thursday morning. This crust is expected to have quickly broken down during the day. In the north of the region, no surface crust formed overnight. On Wednesday, moist surface snow was being reported to mountain tops on all aspects with wet surface snow at treeline and below. A weak crust/surface hoar layer which was buried over a week ago is down 20-30cm in the north of the region. A widespread crust/facet layer buried in early February and a lingering surface hoar layer from January can now be found down a meter or more. Weak basal facets also exist in some areas and have been shown to be most reactive in the north of the region. All these old weak layers still have the potential to produce large avalanches, especially with a large trigger such as a cornice fall. Extra caution is required during this period of substantial warming and intense solar radiation, as this is when these layers have the biggest potential to wake up.

Problems

Deep Persistent Slabs

Deeply buried weak layers which have been dormant recently are expected to wake up this week with the substantial warming and sun exposure. Very large avalanches are expected this week.

Cornice releases have the potential to trigger deeply buried weak layers. >Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >Be aware of the potential for full depth avalanches due to deeply buried weak layers. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 6

Cornices

Large lingering cornices are expected to become weak with the substantial warming and sun exposure this week. They can be destructive by themselves, and may also become the trigger for a large slab avalanche on the slope below.

Give cornices a wide berth when traveling on or below ridges. >Cornices become weak with daytime heating, so travel early on exposed slopes. >Extra caution needed around cornices with current conditions. >

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Loose Wet

Loose wet sluffing is expected on sun exposed slopes during the heat of the afternoon. Very warm conditions may increase the size and run length of natural sluffing.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet. >Avoid travelling on ledges and cliffs where sluffing may have severe consequences. >Be cautious of sluffing in steep terrain. >

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Apr 1st, 2016 2:00PM