Archived

Avalanche Forecast

Mar 3rd, 2017–Mar 4th, 2017

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Lizard-Flathead.

Moderate snowfall amounts and strong to extreme winds has resulted in HIGH avalanche danger at upper elevations. If the region receives less then 20 cm overnight the danger may be CONSIDERABLE.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

Friday Night: Snow amounts 5-20 cm with strong ridgetop winds from the SW. Freezing levels 100-1200 m. Saturday: Mostly cloudy with isolated flurries. Light winds from the SE, alpine temperatures -13 and freezing levels 1100 m.Sunday: Mostly cloudy with snow amounts 10-25 cm. Moderate winds from the S-SW. Alpine temperatures near -5 and freezing levels valley bottom.Monday: Snow 5-10 cm and light winds from the SW. Alpine temperatures near -6.

Avalanche Summary

On Friday, numerous natural and explosive triggered slab avalanches up to size 2.5 were reported. These were seen from N-NE aspects above 1600 m. Some of the crowns were up to a metre deep but I suspect the failures were within the recent storm snow. New snow and strong to extreme SW winds friday night are driving the danger ratings to HIGH for Saturday, however; natural avalanche activity will likely start to taper off through the forecast period. Slab avalanches are primed for human triggering.

Snowpack Summary

A metre of low density storm snow has fallen in the past week. This new snow continues to settle into a denser slab which sits over a variety of old now surfaces including surface hoar, facets (sugary snow), stiff wind slabs, sun crust on solar aspects and a widespread rain crust below 1900 m. The recent storm snow is reportedly showing a poor bond to these older snow surfaces. Strong winds from the SW are redistributing some of the new snow onto leeward slopes, building thicker, stiffer slabs and promoting large cornice growth. Isolated basal weaknesses may still exist in shallow snowpack areas. These weak areas appear to be on north-northeast aspects in the alpine.

Avalanche Problems

Storm Slabs

Storm slabs are primed for rider triggering, especially on leeward slopes and behind terrain features that are wind loaded. Looming cornices exist and failures could initiate slabs on the slope below.

Avoid leeward slopes as a thicker, reactive slabs will likely exist.Avoid all avalanche terrain during periods of heavy loading from new snow and wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Deep Persistent Slabs

There have been two natural deep persistent slab releases in the past week. Both of these avalanches were on northeast aspects in the alpine, and released to size 3 or larger.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Be aware of the potential for large, deep avalanches.

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

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 2 - 4