Avalanche Forecast
Regions: Mt Hood.
Winds were still transporting snow on Friday near 7000 ft where you might find fresh slabs. Lower down the mountain, large wind slabs linger near and above treeline in some locations and might be triggered on unsupported slopes or convex roll-overs. Loose wet and loose dry point releases will need to be managed on steeper slopes where a small slide may be consequential.
Discussion
Snow and Avalanche Discussion
Two recent observations give us confidence that the deep slab is healing sufficiently to remove it from the problem list. On Friday, NWAC Pro Observer Nick Asher traveled in the Newton drainage and dug at 5800 ft on a NE aspect. He found the early February crust down 5-8 ft with connected rounds replacing facets under a very supportable 5-10 cm crust. On Thursday, Mt. Hood Meadows Ski Patrol dug to the same crust on a protected NE aspect in the very narrow elev band, 5300-6000, where the facets had previously been prominent. The facets were also turning to rounds. Given no reported activity for 2 weeks and a stabilizing snow structure in this region of higher concern, we have removed the Deep Persistent Slab as a problem.
Winds have decreased following several periods of moderate to strong generally NE winds over the last 5 days. Winds freshened Tuesday, strong enough to continue transporting snow and building new fresh wind slabs. A previous round of fresh snow and strong NE winds Monday formed wind slabs on atypical aspects.
Snow storms since last Friday night brought 2-3 ft of new snow to the Mt. Hood area. This created ample snow available for transport and excellent near and above treeline, generally right-side up snow in wind-sheltered locations. A professional observation from the bluegrass ridge area found that wind slabs were not impacting the terrain below 5500 ft.Â
Keep in mind that with all the recent snow, loose avalanches will be possible on any aspect. Notably, south-facing aspects may produce roller-balls and small loose wet avalanches during periods of intense sunshine. Faceting upper snowpacks on northerly aspects may run farther than you expect on steeper slopes.
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 Februaryâs 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, weâve experienced three weeks of very cold and snowy conditions. Backcountry travelers frequently reported, âbest conditions in yearsâ. 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. Â
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 âunlikely.â The exception is the East Cascades where a shallow snowpack has preserved buried facets, and persistent slabs will remain possible through the weekend. So, weâre 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 havenât confirmed any avalanches on these shallow weak layers, but they have our attention and weâre 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, itâs anyoneâs guess what specific weather patterns lay in store of us. However, there are two items that stick out in our minds.
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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.
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High elevation travel: Frequently March begins to usher in a period where we push higher and deeper into the mountains. Remember, we donât 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 donât line-up with the avalanche advisory, you may be experiencing a different snowpack. Itâs 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⦠thereâs still plenty of winter left. Stay safe out there.
Avalanche Problems
Wind Slabs
While Professional Observations from Bluegrass Ridge and the Newton Drainage, Wednesday and Friday, respectively, winds have continued to transport snow near 7000 ft and old wind slabs linger in the terrain from a spell of moderate to strong winds that ended on Thursday. In the majority of the terrain you travel in, you are unlikely to experience wind-affected snow on Saturday, but that doesn’t mean you won’t find them. Probe beneath the fluffy surface snow to identify wind-affected terrain, where nearby convex and unsupported slopes are where you are most likely to trigger the slab. Keep in mind that wind slabs may be on atypical aspects due to unusual recent wind directions.
Mt. Hood Meadows Pro Patrol triggered a small soft slab on a SW aspect on Thursday, but found the wind slab problem to be on a healing trend.
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1