Avalanche Forecast

Issued: Mar 30th, 2016 8:03AM

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 persist until Friday evening. Thursday should be sunny with light alpine wind and freezing levels reaching around 3500m in the afternoon. Increasing cloud cover is expected on Friday but mostly sunny conditions are expected for most of the day with freezing levels above 3000m. Alpine winds are expected to increase on Friday evening as the ridge breaks down. A mix of sun and cloud is currently forecast for Saturday with freezing levels dropping to around 1500m and moderate southwest winds in the alpine.

Avalanche Summary

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. No new avalanches were reported on Monday. On Sunday, a natural icefall entrained surface snow and was reported as size 2. Isolated natural wind slabs were reported to size 1 on east aspects at treeline. In the far north, natural cornice releases were reported to have triggered slabs up to size 3.5 which were stepping down to ground. Point releases were reported up to size 2 and glide cracks up to size 2.5. On Thursday, continued warming , sun exposure, and limited overnight recovery means natural cornice releases, deep persistent slab releases, and loose sluffing are expected to continue. Very large avalanches will remain a serious concern for the next few days.

Snowpack Summary

Moist surface snow is being reported to ridgetop on all aspects with wet surface snow at treeline and below. Warm overnight temperatures means there was a limited refreeze of the snow surface. A thin crust may have formed in some areas but is expected to quickly break down in the morning. 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.

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

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

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. Rising freezing levels may increase the size and run length of natural sluffing.

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

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Valid until: Mar 31st, 2016 2:00PM