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Olympics

Issued: 7:59 PM PST Monday, March 5, 2018
by Dennis D'Amico

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

Despite the continued slow stabilizing trend, specific terrain still has the potential to produce large and destructive avalanches. There is still a chance that you could trigger a large Persistent Slab avalanche. This problem is difficult to manage and can break widely, but you can reduce your risk by avoiding open slopes 35 degrees and steeper. Small loose wet avalanches are likely on sun-affected slopes on Tuesday where you are likely to trigger an avalanche on steeper slopes.

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Avalanche Problems for Tuesday

Persistent Slabi

Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.

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Loose Weti

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

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Forecast for Tuesday:

The March sunshine will begin impacting slopes that receive direct sunshine on Monday with anticipated mostly clear weather in the morning and a mix of clouds and sunshine in the afternoon with a slight warming trend during the day. 

Although it is becoming unlikely, you may still be able to trigger Persistent Slab avalanches on slopes 35 degrees and steeper. We think this problem is decreasing in the Olympics because we have no reports of recent avalanche activity, facets have not been found to be widespread and have not been found in association with a crust, so they tend to dissipate over time. However, variability exists across the terrain and persistent slabs have proven to be quite dangerous in the nearby Cascades so reduce your risk by avoiding steep, open slopes and large avalanche path and dig down and check for weak sugar-like facets or buried surface hoar above the most recent firm crust layer formed in early February on all but south aspects before you ski a slope. This crust layer is down about 2-4 feet. 

You are likely to trigger small loose wet avalanches as strong solar radiation moistens the 2.5" of recent surface snow on aspects exposed to direct sunshine. This problem will increase throughout the day until cloud cover limits the problem. Avoid sun-exposed slopes steeper than 35 degrees. A variety of melt-freeze crusts exist within the snow-pack on E-SE-S-SW-W aspects where the loose wet avalanche problem may develop on Tuesday. These crusts should prevent loose wet avalanches from gouging down more deeply and becoming large.

Avalanche Summary:

No recent avalanches have been reported from the Olympics.

Monday's mostly cloudy skies followed light snowfall on Sunday afternoon, bringing 2-3" of new snow with light winds. Up to 2 feet of snow fell near Hurricane Ridge in the past week. Winds as recent as Thursday formed Wind Slabs on a variety of aspects near and above treeline. In sheltered areas generally soft unconsolidated surface snow exists. Large snowdepth differences exist between shallow southerly and deeper northerly aspects. 

On shaded aspects, about 3 ft of of settled snow sits on top of the weak persistent grains (see new observation below) that formed on a strong crust earlier in February that should be healing with time. No recent snowpack tests have been reported on this layer.  On these aspects, there are no other significant layers of concern in the mid and lower snowpack.

A very different and very shallow snowpack exists on south-facing aspects where warm temperatures and sunshine prior to mid-February melted the majority of the snowpack. Much of the snow on south-facing was deposited from mid-february onwards. Basel facets were present on the ground and this will be something to watch if warm temperatures don't round these grains before the next snowfall.

Observations

On Saturday March 3rd, NPS rangers found 2-3 mm buried surface hoar from mid February intact on a NNW aspect at 4990’. The surface hoar was about 4" (10 cm) above a crust 32" (80 cm) below the surface. No new or recent avalanche activity was observed on this layer. The snow depth was much shallower on due south slopes (as little as 1.5 ft deep, recent snow only) as compared to northerly slopes (120" deep). On south-facing aspects, the total snow was 1.5' deep and 1-2 mm basal facets were present on the ground.

On Friday, March 2nd, NPS rangers reported a large avalanche on a recently wind loaded slope. Elsewhere, profiles showed a faceted weak layer buried in mid- February was found 2-4 feet below the surface and was showing some signs of rounding.

No Corresponding Mountain Weather Forecast Available

USE AT YOUR OWN RISK

This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.