Avalanche Forecast

Archived

Feb 23rd, 2019–Feb 24th, 2019

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Below Threshold.

Treeline

Below Threshold.

Below Treeline

Below Threshold.

Regions

Olympics.

You are most likely to encounter lingering wind slabs or loose dry avalanches in the Hurricane Ridge area Sunday. However, uncertainty exists regarding the likelihood of triggering a persistent slab avalanche. Keep this in mind while selecting terrain, keeping in mind that smaller avalanches could be the necessary ingredient to trigger a more isolated but deeper avalanche problem.

Discussion

No new or recent slab avalanches have been reported over the last week in the Hurricane Ridge area. That doesn't mean the weak layers we have been tracking during this unusually cold month aren't hiding in isolated areas, waiting for the right trigger.

NWAC Professional observer Matt Schonwald went looking for reactive weak layer(s) on Thursday in protected north-facing terrain below treeline (5000 ft) at Hurricane Ridge. He found weak snow (2-3 mm facets) down 2.5 ft (75 cm). There was a different and more recently buried weak layer (buried surface hoar) down 1 ft (30 cm).

In snowpack tests, both layers were stubborn to trigger, but are on still on our radar because if triggered could produce large avalanches that break widely across terrain features. Observations suggest the weak layers are healing more rapidly on southerly aspects versus shaded aspects.

Forecast schedule

For the 2018-19 winter season, avalanche danger ratings will be issued for the Olympics every Friday through Sunday and during mid-week holidays.

During the week, No Rating will be issued but forecasts will include expected conditions and relevant travel advice. While this avalanche forecast is focused on backcountry avalanche conditions expected in the Hurricane Ridge area, we want to hear about your observations from other parts of the Olympics as well.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.