Archived

Avalanche Forecast

Jan 12th, 2019–Jan 13th, 2019

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: Cascades - East.

The Bottom Line: We are in a low probability, but high consequence scenario for avalanches that could break into old snow layers. Upper elevations are the main concern for these, and for shallow, wind slabs that may build from light winds. Loose avalanches will become possible with strong sun and warming temperatures during the middle of the day.

Snow and Avalanche Discussion

Folks looking to get into the high mountains should realize that there is a fair amount of uncertainty with our snowpack above 6,000ft, with the warming, and there is a lot of variability within the zone. A common structure to be found out there will be storm snow (with or without a wind slab) over a crust from January 3rd. The storm snow from January 8/9 may not be bonding very well to the crust at upper elevations, where a thin layer of weaker snow has been found just above this crust. Recent wind slab avalanches ran on the crust at Mission Ridge and were from 6" to 16" deep and from 60' to 125' wide. One started on a Northwest aspect at 6300ft and broke through the crust into weak snow near the ground. At low elevations and on southerly aspects, a number of loose wet avalanches have been observed.

Avalanche Problems

Wind Slabs

It has been a number days since the big east wind event, but at the higher elevations the wind has been drifting the low density snow surface into thin wind slabs here and there. The recent east winds formed slabs in some unusual locations like well below ridgelines, on the sides of gullies, and in places that are often scoured. Other locations have no wind slabs at all. Use visual clues of the snow surface texture to help you find where these areas may be. Wind slabs often feel firm, and hollow underfoot. Approach steep slopes with caution, and be especially careful of steep, unsupported, and rocky slopes. Ease into avalanche terrain by using smaller, less consequential slopes first. You can stay safe by traveling on ridges, and low angle and well supported slopes.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 2

Persistent Slabs

We are in a low probability, but still high consequence timeframe for deeper avalanches in old snow. Obvious clues to danger like shooting cracks, or whumphs may not be observed. This is why persistent slabs are difficult to assess and predict. We still have a weak snowpack structure in some locations and there is plenty of snow over these layers to act as a slab. The snowpack is slowly adjusting to the new load, but rapidly rising freezing levels and the sun are something to consider in that it may influence the reactivity of these slabs. In any case, slides on these deeper weak layers could be very large and life threatening. You can choose to minimize your risk by using low angle, and well supported slopes, and staying out of radical terrain.

There are two primary layers of concern in the snowpack:

A layer of buried surface hoar may be found 1-3 ft below the snow surface. This is mainly a concern above 6000ft. Be suspicious of this layer the higher you go. Documented avalanches have been on North through Southeast aspects. Snowpack tests continue to reveal sudden results in some areas on this layer.

A layer of weak sugary facets can be found near the ground, particularly in the eastern edge of the forecast zone such as Mission Ridge and Blewett Pass. If an avalanche failed on this layer, it could be more than 4 feet deep. Use caution if you are traveling in areas where the snowpack is thinner.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely

Expected Size: 3 - 3

Loose Wet

With sky rocketing freezing levels for the upper elevations, and sun in the forecast, loose wet avalanches may become common. Steep slopes that face the sun are the most likely places these will happen. If you see roller balls, notice the snow surface is becoming wet and sticky, or see small loose slides that begin entraining snow on any aspect, get off of steep slopes.

Aspects: South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2