Avalanche Forecast
Regions: Snoqualmie Pass.
A storm brining precipitation and wind at Snoqualmie Pass Friday isn’t likely to be enough to significantly impact the avalanche danger. You may find isolated avalanche hazards at higher elevations where the wind drifts the new snow or in very wet punchy snow at lower elevations.
Discussion
Snow and Avalanche Discussion
A series of storms will begin to impact the Snoqualmie Pass area Friday bring several rounds of precipitation, fluctuating snow levels, and strong winds. Unfortunately, the weather models diverge on the strength and timing of each wave of precipitation. This is making pinning down the avalanche forecast difficult. As a result, you’ll need to monitor conditions and recognize when your experiencing weather that’s outside the forecast. If your observations don’t line-up with what you expected, dial back your travel to lower angled and lower consequence slopes.
This first round of precipitation Friday doesn’t look like it will be enough to build new avalanche concerns and increase the avalanche danger for Snoqualmie Pass. That’s likely to change as additional storms impact the area over the weekend. If you travel to higher elevations Friday, be on the lookout for areas where the wind drifts any new snow into slightly deeper drifts. It’s these wind affected areas where you may find an isolated slab.
Warm temperatures and rain continue to cause the snowpack at mid and lower elevations to fall apart. We’re seeing opening creeks, snow shedding from rocks, holes near trees, and even bare ground. More water on Friday will only serve to fuel this pattern. Use caution as you travel near these springtime hazards, and expect the snow coverage to be different than you experienced in recent weeks.
We expect similar springtime hazards such as these glide cracks, exposed rocks, and openings seen on Mt Herman at 4300 ft. Â 04/03/19 Photo: Andrew Kiefer
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
Loose Wet
Don’t ignore the addition of water as rain into the snowpack Friday. While most locations should handle the influx of water well, you could find a few areas where wet punchy snow creates loose wet avalanches. You’re most likely to find loose wet avalanches on mid-elevation shaded aspects where the snow hasn’t undergone a significant spring transition. Be leery of steep slopes where you experience deep wet snow. Even small loose wet avalanches can harm you if they push you into creeks, down gullies, or over cliffs.
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1