Avalanche Forecast
Regions: Olympics.
You can trigger a small wind slab at upper elevations where increasing high elevation snow and wind will transport shallow fresh snow. Make observations of recently formed snow drifts and avoid steep, slopes that receive fresh snow loading. Take normal springtime precautions around drooping cornices, heavy wet snow, opening creeks and widening glide cracks.
Discussion
Snow and Avalanche Discussion
The Hurricane Ridge area received light rain on Wednesday that brought 2-3†of new snow to higher terrain. On April 4th, Pro Observer Matt Schonwald reports that there was some very shallow and small loose wet avalanche activity with this new snow at higher elevations, but that it is settling well.
The mountains are still experiencing their spring transition. On his Hurricane Ridge traverse, Matt Schonwald also found that south-facing slopes at higher elevations were losing snow rapidly with 4 ft or less of snow even above 6000 ft. Plenty of bare ground is showing. North and NE slopes had many glide cracks, but these can be present on any aspect. Reports from around the region have indicated that creeks are opening up with snow bridges collapsing. Cornices are sagging. Use caution if you travel near these features. Expect low snow cover everywhere below 4500 ft, so watch for barely submerged terrain features.
While we generally think the snowpack is well-settled and snow surfaces at lower elevations have transitioned to spring melt-freeze, if you are in an area that receives heavier rain, watch for soft, wet snow more than ankle deep where you can still trigger a Loose Wet avalanche on steeper slopes.
The spring transition has come early and you may find many unexpected hazards in your terrain including drooping cornices, opening creeks and holes, and many widening glide cracks.
Highly variable snow depth by aspect. Hurricane Ridge Traverse. 04/04/2019. Photo Credit: Matt Schonwald
Snowpack Discussion
April 3rd, 2019
Spring snowmelt
The snowpack in much of the Cascades has changed dramatically in the past two weeks. The weather has shifted solidly to spring-like patterns. The spring warm-up started in mid-March with a prolonged period of relatively clear skies and warm temperatures. Moving into April, we’re seeing periods of unsettled spring weather bringing rain to many low and mid-elevation slopes and snow to upper elevations.
Very bare southeast aspects of Rock Mtn/Nason Ridge. April 2nd. Photo: Josh Hirshberg
Since the peak height of snow in mid to late February, mountain weather stations in the 4,000-5,000ft range show an average of 27% decrease in height of snow. Looking at weather stations in nearly every zone, the percentage decrease ranged from 22-29%. This year's spring snowmelt is much earlier than normal. Traveling in the mountains the loss of snow coverage is most noticeable on southerly, sun-exposed slopes and below 4,000ft. On northerly aspects and slopes above 5,500ft, the snowpack has seen less dramatic changes and has even maintained some dry layers.
NWAC climatological snow depth data from April 1st. You can view it on our website here.
Spring avalanche considerations
As you head into the mountains there are a few questions to ask yourself common to spring avalanche conditions:
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Is there any recent snow accumulation that could cause avalanches? If so, what kind of avalanches could you trigger? And where?
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What are the high and low temperatures of the past 24 hours as well as the forecasted temperatures during the time you’ll be in the mountains? Could these create weak, wet snow surfaces?
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How is the cloud cover contributing to the melting or freezing of surface snow? Did clear skies allow for a sufficient overnight freeze? Will the sun be strong enough to weaken surface layers?
Glide avalanches and holes opening up in rocky terrain near Mount Herman. Photo: Andrew Kiefer
Other considerations
In addition to daily avalanche hazard, the early snowmelt is creating some other travel considerations. Some roads and lower elevation slopes may not have enough continuous snow coverage for travel on snow machines. Holes melted around rocks, trees, and creeks could create a fall hazard. When nighttime temperatures and cloud cover allow for surface freezes, bring appropriate equipment to mitigate slip and fall hazard on steep slopes.
We are approaching the end of our daily avalanche forecasting season. The mountain weather forecast will continue into the spring, and the weather station data is available year round. Keep checking the forecast for conditions updates on the end of season information.
Avalanche Problems
Wind Slabs
Wind slabs will be developing during the day on Friday and your risk of triggering a growing wind slab increases through the afternoon as the snowfall and wind increases. Snow levels dropping to near or slightly below Hurricane Ridge proper means that slabs will be confined to upper elevation terrain features and start zones. The danger depends upon the amount of new snow and the strength of the winds, both of which are difficult to forecast with marginal snow levels and multiple systems arriving. Look for blowing and drifting snow as signs that wind slabs may be present in your terrain. If these drifts are more than 6” deep, use ridgelines and slopes less than 35 degrees to more safely avoid wind-loaded slopes.
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.
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.
Likelihood: Possible
Expected Size: 1 - 1