Avalanche Forecast

Snow and Avalanche Discussion

The most important piece of tonight’s forecast is to be aware that conditions are changing as we return, albeit temporarily, to winter. Snowfall will pick up during the morning and should produce less than 6”, but winds will blow the new snow around. Watch for areas where wind drifts are more than 6” thick or you find punchy snow surfaces.

This next system should be colder and wetter than Friday’s storm. Unfortunately, the models continue to struggle with each round of precipitation. We are confident that it’s going to be stormy, and that the precipitation will be enough to increase the avalanche danger throughout the day Saturday. You’ll need to pay attention to the conditions around you and determine if the weather you’re experiencing lies outside of the forecast. When you see observations that don’t line-up with what you expected, dial back your travel to lower angled slopes.

The wet weather pattern is expected to continue Saturday night and Sunday with more precipitation and potentially warming temperatures. This will continue to increase the avalanche danger. As more snow piles up, and snow levels fluctuate, we could be looking at very dangerous avalanche conditions this weekend.

The East South zone generally picked up less than 0.5” of water in the 24 hours ending Friday evening. Elevations below 4500 ft have remained warm for some time and Friday night may be the first really solid freeze in many areas for some time. The snowpack doesn’t always heal overnight. If you find snow where you sink in deeper than your ankle, reduce your exposure to slopes steeper than 35 degrees. It is these steeper slopes where an avalanche may gouge more deeply and run the scale of the terrain feature.

The mountains are still experiencing their spring transition. Creeks are opening up with snow bridges collapsing. Glide cracks are evident and may release in generally predictable locations, but without warning. Sagging cornices may fail. Use caution if you travel near these features.

In the East South zone, many steep sunny aspects and low elevations that previously had a shallow snowpack have melted out for the season.

Forecast Schedule and No Rating

At this time, we do not have enough specific snowpack information to issue an avalanche hazard rating for the East Slopes South zone. However, even when No Rating is applied, applicable avalanche conditions and backcountry travel advice will be provided throughout the season. When weather systems produce very dangerous avalanche conditions in adjacent zones, NWAC will issue an avalanche warning for this zone as well.

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:

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?

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.