Avalanche Forecast

It is turning back to winter in the high country. A stormy weekend is on tap, with avalanche danger on the rise. For Saturday morning, you may find a good overnight refreeze at the lower elevations. Cooling temperatures and increasing winds with some more snow at higher elevations may create wind slabs to be careful of. Dangerous conditions look to develop by Saturday night/Sunday in the mountains with potentially very heavy snowfall and rain. There is some uncertainty with the weather forecast, but if it all pans out, another round of heavy precipitation with warming temperatures and very strong winds are headed our way on Sunday. Large avalanches may become very likely, and may run to lower elevations. 

Previously, our avalanche problems have been driven by warm temperatures and a melting snowpack. On April 1st, an observer in the Eightmile Lake area found a very large recent wet loose slide off the west face of Colchuck Peak that may have been initiated by rockfall. See photo below. This is an example of the weak nature of the melting snowpack. If something large does initiate a slide, lots of snow may entrain on the way down. Weak and unsupportable wet snow has been found in many areas, especially in shallow areas near rocks. Be sure to consider all the hazards that come with spring in the mountains. Factor in a good margin for error as hard to predict events like cornice fall, glide avalanches, icefall, rockfall, and a general “shed cycle” in the mountains have been ongoing. 

Very large loose wet slide that gouged down to the ground, and may have been initiated by rockfall. Beneath the west face of Colchuck Peak. Observed on April 1, 2019.

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.