Stevens Pass

Wind slabs may be surprisingly wide, and easy to initiate at mid and upper elevations. Loose avalanches may run far, entraining lots of snow. Travel conservatively and evaluate the bonding of the storm snow carefully. 

Observers on Thursday found a few small (5" deep x 40' wide) natural wind slabs in East Highlands Bowl. Multiple observers found very reactive conditions where wind slabs formed near ridgelines with the 3-5" of new snow that fell during the day. The recent snowfall has buried some weak surfaces. The new snow is not bonding well initially, particularly on southerly aspects where the new snow sits over a melt freeze crust, often found with facets above. Small dry loose avalanches were observed to run far on steep, sheltered slopes near Mt. Howard. There is some uncertainty with the weather forecast, in turn influencing the avalanche danger. If a convergence zone does set up, we are likely to be at Considerable danger tomorrow for the pass. 

Thin layer of large grained facets over a crust found on a south aspect at 5,600ft on Arrowhead on 3/7. Avalanches may be easily triggered and quite wide on this set up.

March 4, 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 recording near or just 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 many areas, there has been a lack of avalanche activity and snowpack tests have been less reactive. 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 until the sensitivity drops further. 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, predominantly from the east, 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 Glass

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 avalanches conditions change with natural loose avalanches originating from sunny slopes, surface snow becoming thick and heavy, and slabs taking on a moist to wet snow character. 

• 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.