Avalanche Forecast

Archived

Apr 7th, 2019–Apr 8th, 2019

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

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Another round of warming temperatures and additional precipitation will maintain dangerous avalanche conditions Sunday night and Monday. Wet snow and new snow avalanche problems can overlap near and above treeline, so choose your terrain and exposure to overhead hazards wisely.

Discussion

Snow and Avalanche Discussion

An active weather pattern that has dumped 10-14” of heavy snow above 4500’-5000’ in the West South zone since Friday will return Sunday night and Monday. Once again the bulk of the heavier precipitation should stay aimed into Oregon but the West South zone is on the periphery between light to moderate versus heavy accumulation. There is higher confidence that snow levels will rise to about 6000’ during the day on Monday. Monitor the weather, and recognize how the conditions you’re experiencing differ from the forecast.

Observations from both Paradise and Crystal reported large natural wet loose avalanches on Sunday running over the wet old snow interface. Crystal Patrol reported sensitive 2-4’ wind slabs releasing on north aspects above 6000’.

Even though the recent weather felt like winter, there are several springtime hazards in the mountains. Creeks, particularly at low elevations, opened wide during the recent warm weather. Glide cracks continue to grow and a few glide avalanches have occurred. Holes appeared near many trees and rock. Cornices continue to sag overhead. Use caution when you travel near any of these spring hazards that could be hidden by a few inches of new snow.

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.

A natural loose wet avalanche (D1), Lichtenberg Mtn, N, 4,850ft. 4/7/2019. Photo: Will Govus

Spring avalanche considerations

As you head into the mountains there are a few questions to ask yourself common to spring avalanche conditions:

Is there any recent snow accumulation that could cause avalanches? If so, what kind of avalanches could you trigger? And where?
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?
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?

Debris from a natural loose wet avalanche (D2), Lichtenberg Mtn, SW, 5,000ft. 4/7/2019. Photo: Josh Hirshberg

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.

Glide avalanches and holes opening up in rocky terrain near Mount Herman. Photo: Andrew Kiefer

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the 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. 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.