Archived

Avalanche Forecast

Jan 2nd, 2020–Jan 3rd, 2020

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

2: Moderate

The avalanche danger rating below treeline will be moderate

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

2: Moderate

The avalanche danger rating below treeline will be moderate

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: Lizard-Flathead.

Natural avalanche activity has tapered but human triggered storm slab avalanches are still possible. Expect elevated avalanche danger in the alpine if freezing levels exceed 1700m.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

Thursday night: Mostly cloudy with clear periods, scattered flurries accumulating up to 5 cm, moderate wind from the west, alpine temperature around -7 C.Friday: Mostly cloudy with scattered flurries, moderate wind from the southwest, alpine high temperature -2 C, freezing level rising to at least 1500 m possibly higher.

Saturday: 5-10 cm of snow, moderate to strong wind from the southwest, alpine high temperature -3 C, freezing level dropping to valley bottom.

Sunday: A trace of snow, moderate wind from the southwest, alpine high temperature -4 C, freezing level rising to 1500 m before dropping to valley bottom overnight.

Avalanche Summary

Many large (size 2-3) storm slab avalanches both natural and explosive triggered, were reported on Wednesday. Continued explosive work on Thursday produces size 2 storm slab avalanches. Expect to see continued natural storm slab activity if the freezing levels rise above 1500 m on Friday.

We are sorry to report the news of 2 fatalities in the Montana Flathead region on Wednesday. The bed surface of the deadly avalanche was a crust formed and buried around Christmas. An illustrated photo can be found here. This crust has been observed widely in the Lizard Flathead region as well.

Snowpack Summary

The recent snow has settled into a dense slab amid warm temperatures and wind. A thin lens surface crust can be found in some places below treeline. Below 1700 m a hard, thick crust formed around Christmastime is buried 50-70 cm. Surface hoar has been occasionally been observed ontop of this crust. Hard snow in the mid snowpack sits above faceted snow and crusts near the bottom of the snowpack (100-170 cm deep). This weak lower snowpack has not been an active avalanche problem recently.

Terrain and Travel

Keep in mind that human triggering potential persists as natural avalanching tapers off.
Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Extra caution for areas experiencing rapidly warming temperatures for the first time.

Avalanche Problems

Storm Slabs

Natural activity tapered on Thursday but human triggering remains possible. Sensitivity to triggering may increase if the freezing levels rise higher than 1700 m on Friday, as high elevation snow will experience rapid warming for the first time.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2.5