Avalanche Forecast

Issued: Mar 2nd, 2019 10:00AM

The alpine rating is below threshold, the treeline rating is below threshold, and the below treeline rating is below threshold.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Email

If you see evidence of wind affected snow, steer away from features where you are more likely to trigger an avalanche such as convex rollovers, unsupported slopes, or complex terrain. Weak snowpack structures likely in the eastern portions of this zone and a deep persistent slab identified in neighboring zones are still on our minds. If you are considering traveling in larger avalanche terrain, stop and consider the consequences of a large or very large avalanche breaking on your slope.

Summary

Discussion

Snow and Avalanche Discussion

Areas in the far eastern portion of this zone have a shallow and far weaker snow structure. You will need to test these snowpacks for reactive lays of facets or crust/facet combinations before committing to open slopes. Where enough snow exists to ski or ride, you can produce avalanches.

There’s plenty of wind affected snow around the southern Washington Cascades, but any wind slabs formed during recent wind events are now a few days old and hard to trigger. If you see signs of wind transported snow, be leery of convex rollovers, unsupported slopes, and complex terrain where you might be more likely to trigger an avalanche. In some locations, these old wind slabs may be covered by an inch or two of soft snow.

On Friday and again Saturday, cloudy skies, in many areas, did not allow the sun to significantly affect southerly aspects. Even though air temperatures are expected to be cold, if the sun comes out, natural small loose avalanches may release on steep rocky slopes. This issue is easy to manage. Don’t linger below steep sunny slopes during periods of prolonged sunshine.

The upper snowpack: Observations from the field in neighboring zones indicate variable snow surface conditions. You may encounter soft dry snow, stiff wind slabs, very firm surfaces, or breakable crusts. We have been tracking two layers of buried surface hoar and/or facets in the upper snowpack. Snowpack tests are doing a great job of highlighting these layers. So far, there haven’t been any avalanches on these layers. Recent observations indicated these layers are rounding and gaining strength.

We are still talking about a deep persistent slab layer even though there haven’t been any avalanches on this layer in more than a week.  The nearby West-South zone experienced the most recent avalanche activity on this layer of old weak facets 3-5 ft below the snow surface. Snowpack tests from this past week continued to demonstrate this layer is present, can fail, and could produce an avalanche. So, what do we do with that information? Before you engage with large avalanche slopes, stop and consider the risk. Be suspicious of complex terrain, locations where the snowpack is thinner, or places where you might find larger triggers such as other avalanches. Yes, this layer is gaining strength and would be very difficult to trigger, but the consequences would be extremely high if you find the wrong spot.

We are tracking two weak-layers in the upper snowpack. You may find layers of buried surface hoard and/or facets in the upper few feet of the snowpack. So far we have not confirmed any avalanches on these layers. Keep these layers in mind if you travel to higher or more remote locations where less information is available.

Tilt-test highlighting a layer of buried surface hoar 15” below the snow surface near White Pass.

Forecast Schedule and No Rating

At this time, we do not have enough specific snowpack information to issue an avalanche hazard rating for the East Slopes South zone. However, even when No Rating is applied, applicable avalanche conditions and backcountry travel advice will be provided throughout the season. When weather systems produce very dangerous avalanche conditions in adjacent zones, NWAC will issue an avalanche warning for this zone as well.

Snowpack Discussion

March 1, 2019

Here we are at the beginning of March. The days are noticeably longer, the sun feels warmer, but the winter is far from over. This may be a good time to take stock of February’s events, where we are now, and what we might expect in the future.

A February to Remember

Many longtime Cascade travelers continue to remark about the long span of high-quality travel conditions in February. Indeed, we’ve experienced three weeks of very cold and snowy conditions. Backcountry travelers frequently reported, “best conditions in years”. February also saw a few rounds of natural and human triggered avalanches. These avalanches were different from our more frequent Cascade storm slabs; here today and gone tomorrow. Most avalanches failed on buried weak persistent layers. As such, most zones spent much of February with Persistent or Deep Persistent Slabs in their forecasts.

Natural avalanche in Icicle Creek Feb 13, 2019. Photo: Matt Primomo

With the notable absence of high elevation rain events, snowpacks around the northwest grew remarkably. On the west slope, most weather stations added 2-4 ft of snow depth. East-side locations added 1-2 ft. Mt Hood locations added 4-5 ft. Even with these impressive snowpack growths, many Cascade Snotel sites are still recording below average snow depths for the winter.  

During most of February, snow conditions were soft and powdery making for fun recreating in many areas. Photo Matt Primomo.

Where We Are Now

Lack of avalanche activity on the layer of buried facets from Feb 8 allows us to gain confidence in many areas. In some areas, snowpack tests are showing less than sudden results. These two pieces combined have allowed us to drop persistent slabs from some forecasts and shift others to “unlikely.” The exception is the East Cascades where a shallow snowpack has preserved buried facets, and persistent slabs will remain possible through the weekend. So, we’re out to the woods, right? Well, maybe. The same cold and stormy weather that brought us excellent snow quality, also allowed us to bury new weak layers. So far we haven’t confirmed any avalanches on these shallow weak layers, but they have our attention and we’re tracking them.

Recently our attention shifted to the upper snowpack. Recent avalanche problems have largely focussed on wind transported snow. Several wind events from various directions placed wind slabs on a variety of aspect. With the colder than normal temperatures, wind slabs may not heal as quickly as normal.

A small natural wind slab avalanche in the Crystal Mt backcountry. Photo; Dallas Glas

What Might We Expect

As we move into March, it’s anyone’s guess what specific weather patterns lay in store of us. However, there are two items that stick out in our minds.

  • The strength of the March sun: You can already feel it just walking around town. As the sun creeps higher into the sky and the days grow longer, the sun can have a greater impact on the snow surface. When the sun comes out, expect things to change quickly. You may see slab avalanches become easier to trigger, natural loose avalanches originating from sunny slopes, or surface snow become thick and heavy. Remember, the sun frequently brings change.

  • High elevation travel: Frequently March begins to usher in a period where we push higher and deeper into the mountains. Remember, we don’t have as much information about these far-flung locations. If you use the longer days of March to travel to bigger objectives, keep your eyes open. When observations don’t line-up with the avalanche advisory, you may be experiencing a different snowpack. It’s times like these we need to stop and reevaluate.

Mt Baker on a nice day in early February. Photo: Lee Lazzara

February was amazing! but March is here… there’s still plenty of winter left. Stay safe out there.

Valid until: Mar 3rd, 2019 10:00AM