Archived

Avalanche Forecast

Dec 10th, 2017–Dec 11th, 2017

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

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

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

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

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: Northwest Inland.

Warming and solar radiation will drive the avalanche danger on Monday. Use extra caution in sun-exposed terrain and limit your exposure to large overhead slopes.

Confidence

Low - Freezing levels are uncertain on Monday

Weather Forecast

Sunday night: 3-6mm of precipitation / Moderate southerly winds / Freezing level at about 2000mMonday: Mainly clear / Moderate southerly winds / Freezing level at about 2000mTuesday: 2-5cm of new snow / Moderate southerly winds / Freezing level at 1700mWednesday: Mix of sun and cloud / Light and variable winds / Freezing level at 2300m

Avalanche Summary

No new avalanches have been reported, however it is expected that warm alpine temperatures and sunshine initiated natural activity on steep solar aspects at higher elevations on Sunday.

Snowpack Summary

With the recent temperature inversion, solar and temperature crusts are expected to have formed on sun-exposed slopes, while stiff, stubborn wind slabs linger in lee alpine terrain. Approximately 30-50 cm of storm snow now overlies two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Although snowpack tests have previously shown hard results at these crust interfaces, more recent observations have been limited. Below these crusts, a well settled mid-pack overlies the late October crust near the base of the snowpack. This "crust/facet combo" layer is widespread and has been reactive to rider and remote triggers. It also continues to produce sudden snowpack test results. Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine. (Depths of up to 210 cm have been reported from the Howsons.)

Avalanche Problems

Loose Wet

With precipitation forecast for Sunday night (and then sun on Monday), I would expect loose wet avalanches to occur, especially in steep, sun-exposed terrain where dry snow is exposed to solar radiation for the first time

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.Use caution above cliffs where small avalanches may have severe consequences.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2

Deep Persistent Slabs

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer should be on a strengthening trend, but a heavy trigger in a thin snowpack area or warming may still be enough to cause it to react.

Be aware of the possibility for full depth avalanches due to deeply buried weak layers.Be especially cautious in shallow snowpack areas where triggering a deeper layer may be easier.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3

Wind Slabs

At elevations where Sunday night's precipitation falls as snow, thin yet dense wind slabs can be expected. Watch for triggering in higher elevation, wind-exposed terrain.

If triggered, wind slabs may step down to deeper layers and result in large avalanches.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Possible - Likely

Expected Size: 1 - 2