Avalanche Forecast

The West Central zone received quite a bit of water in the past week, mostly in the form of rain with high elevation snow. Over the weekend, a slight cooling trend lowered snow levels to 4000ft, and the most recent precipitation from Saturday and Sunday translated into 10-12in of new snow in most areas near and above treeline. Expect cloudy skies overnight Sunday, and up to .25in of water with 5000ft snow levels during the day Monday.  

Sunday brought light precipitation with fluctuating snow levels and rain as high as 5000ft. Skier triggered wet loose slides (D2) were reported near and below treeline in the adjacent Stevens Pass zone. The new snow is dense and heavy and has capped old snow layers that are saturated and unconsolidated. The new snow has bonded well to the old snow surface, but density breaks within new/wind loaded snow exist at upper elevations. Also, keep in mind that melting cornices, widening glide cracks, and opening creeks continue to pose a hazard during this spring transition. Give these a wide berth and be heads up as the recent snow may hide these and other obstacles.

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:

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

2. 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?

3. 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